W3C

Web Services Description Language (WSDL) Version 2.0 Part 0: Primer

W3C Working Draft 10 May 2005

This version:
http://www.w3.org/TR/2005/WD-wsdl20-primer-20050510
Latest version:
http://www.w3.org/TR/wsdl20-primer
Previous versions:
http://www.w3.org/TR/2004/WD-wsdl20-primer-20041221
Editors:
David Booth, W3C Fellow / Hewlett-Packard
Canyang Kevin Liu, SAP Labs

This document is also available in these non-normative formats: postscript, PDF, XML, and plain text.


Abstract

This document is a companion to the WSDL 2.0 specification ( Web Services Description Language (WSDL) Version 2.0 Part 1: Core Language [WSDL 2.0 Core Language] , Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts [WSDL 2.0 Adjuncts] ). It is intended for readers who wish to have an easier, less technical introduction to the main features of the language.

This primer is only intended to be a starting point toward use of WSDL 2.0, and hence does not describe every feature of the language. Users are expected to consult the WSDL 2.0 specification if they wish to make use of more sophisticated features or techniques.

Finally, this primer is non-normative . Any specific questions of what WSDL 2.0 requires or forbids should be referred to the WSDL 2.0 specification.

Status of this Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This is the second W3C Working Draft. It has been produced by the W3C Web Services Description Working Group, which is part of the W3C Web Services Activity.

This is the first complete draft of the primer. A diff-marked version against the previous version of this document is available. Comments on this document are invited and should be sent to the public public-ws-desc-comments@w3.org mailing list (public archive).

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document has been produced under the 24 January 2002 Current Patent Practice as amended by the W3C Patent Policy Transition Procedure. Patent disclosures relevant to this specification may be found on the Working Group's patent disclosure page. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) with respect to this specification should disclose the information in accordance with section 6 of the W3C Patent Policy.


Short Table of Contents

1. Introduction
2. WSDL 2.0 Basics
3. WSDL 2.0 Infoset, Schema and Component Model
4. More on Message Types
5. More on Interfaces
6. More on Bindings
7. Advanced Topics
8. References
A. Acknowledgements (Non-Normative)


Table of Contents

1. Introduction
    1.1 Prerequisites
    1.2 Structure of this Primer
    1.3 Notational Conventions
2. WSDL 2.0 Basics
    2.1 Example Scenario: The GreatH Hotel Reservation Service
    2.2 Getting Started: Defining a WSDL Target Namespace
        2.2.1 Explanation of Example
    2.3 Defining Message Types
        2.3.1 Explanation of Example
    2.4 Defining an Interface
        2.4.1 Explanation of Example
    2.5 Defining a Binding
        2.5.1 Explanation of Example
    2.6 Defining a Service
        2.6.1 Explanation of Example
    2.7 Documenting the Service
        2.7.1 Explanation of Example
3. WSDL 2.0 Infoset, Schema and Component Model
    3.1 WSDL 2.0 Infoset
    3.2 WSDL 2.0 Schema and Element Ordering
    3.3 WSDL 2.0 Component Model
4. More on Message Types
    4.1 Embedding XML Schema
    4.2 Importing XML Schema
    4.3 Summary of Import and Include Mechanisms
5. More on Interfaces
    5.1 Interface Syntax
    5.2 Interface Inheritance
    5.3 Interface Faults
    5.4 Interface Operations
        5.4.1 Operation Attributes
        5.4.2 Operation Message References
            5.4.2.1 The messageLabel Attribute
            5.4.2.2 The element Attribute
            5.4.2.3 Multiple infault or outfault Elements
        5.4.3 Understanding Message Exchange Patterns (MEPs)
        5.4.4 Defining New Message Exchange Patterns (MEPs)
6. More on Bindings
    6.1 Syntax Summary for Bindings
    6.2 Reusable Bindings
    6.3 Binding Faults
    6.4 Binding Operations
    6.5 The SOAP Binding Extension
        6.5.1 Explanation of Example
    6.6 The HTTP Binding Extension
        6.6.1 Explanation of Example
    6.7 HTTP GET Versus POST: Which to Use?
7. Advanced Topics
    7.1 Extensibility
        7.1.1 Optional Versus Required Extensions
        7.1.2 Scoping of the wsdl:required Attribute
    7.2 Features and Properties
        7.2.1 SOAP Modules
        7.2.2 Abstract Features
        7.2.3 Properties
    7.3 Import mechanism and authoring style
    7.4 Multiple Interfaces for the Same Service
    7.5 Web Service Versioning
        7.5.1 Compatible Evolution
        7.5.2 Big Bang
        7.5.3 Combined Approaches
    7.6 MTOM Support
    7.7 RPC Style
    7.8 Enabling Easy Message Dispatch
    7.9 Service and Endpoint References
        7.9.1 The Reservation Details Web Service
        7.9.2 The Reservation List Web Service
        7.9.3 Reservation Details Web Service Using HTTP Transfer
        7.9.4 Reservation List Web Service Using HTTP GET
    7.10 Importing Schemas
        7.10.1 Schemas in Imported Documents
        7.10.2 Multiple Inline Schemas in One Document
        7.10.3 The schemaLocation Attribute
            7.10.3.1 Using the id Attribute to Identify Inline Schemas
    7.11 Mapping to RDF and Semantic Web
        7.11.1 RDF Representation of WSDL 2.0
    7.12 Notes on URIs
        7.12.1 XML Namespaces and Schema Locations
        7.12.2 Relative URIs
        7.12.3 Generating Temporary URIs
8. References
    8.1 Normative References
    8.2 Informative References

Appendix

A. Acknowledgements (Non-Normative)


1. Introduction

1.1 Prerequisites

This primer assumes that the reader has the following prerequisite knowledge:

  • familiarity with XML (Extensible Markup Language (XML) 1.0 (Second Edition) [XML 1.0], XML Information Set [XML Information Set]) and XML Namespaces (Namespaces in XML [XML Namespaces]);

  • some familiarity with XML Schema (XML Schema Part 1: Structures [XML Schema: Structures] XML Schema Part 2: Datatypes [XML Schema: Datatypes]);

  • familiarity with basic Web services concepts such as Web service, client, and the purpose and function of a Web service description. (For an explanation of basic Web services concepts, see Web Services Architecture [WS Architecture] Section 1.4 and Web Services Glossary [WS Glossary] glossary. However, note the Web Services Architecture document uses the slightly more precise terms "requester agent" and "provider agent" instead of the terms "client" and "Web service" used in this primer.)

No previous experience with WSDL is assumed.

1.2 Structure of this Primer

Section 2 presents a hypothetical use case involving a hotel reservation service. It then proceeds step-by-step through the development of a simple example WSDL 2.0 document that describes this service:

  • The types element describes the kinds of messages that the service will send and receive.

  • The interface element describes what abstract functionality the Web service provides.

  • The binding element describes how to access the service.

  • The service element describes where to access the service.

Section 3 gives more information on defining message types.

Section 4 gives more information on interfaces.

Section 5 gives more information on bindings.

Section 6 gives more information on defining services.

Section 5 covers various advanced topics, including features and properties, flexible authoring styles, service and endpoint references, use of URIs, etc.

1.3 Notational Conventions

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

This document uses several XML namespaces, some of which are defined by standards, and some are application-specific. Namespace names of the general form "http://greath.example.com/..." represent application or context-dependent URIs [IETF RFC 2396].Note also that the choice of any namespace prefix is arbitrary and not semantically significant (see [XML Information Set]).

2. WSDL 2.0 Basics

This section introduces the basic concepts used in WSDL 2.0 through the description of a hypothetical hotel reservation service. We start with a simple scenario, and later add more requirements to illustrate how more advanced WSDL 2.0 features may be used.

2.1 Example Scenario: The GreatH Hotel Reservation Service

Hotel GreatH (a fictional hotel)) is located in a remote island. It has been relying on fax and phone to provide room reservations. Even though the facilities and prices at GreatH are better than what its competitor offers, GreatH notices that its competitor is getting more customers than GreatH. After research, GreatH realizes that this is because the competitor offers a Web service that permits travel agent reservation systems to reserve rooms directly over the Internet. GreatH then hires us to build a reservation Web service with the following functionality:

  • CheckAvailability. To check availability, the client must specify a check-in date, a check-out date, and room type. The Web service will return a room rate (a floating point number in USD$) if such a room is available, or a zero room rate if not. If any input data is invalid, the service should return an error. Thus, the service will accept a checkAvailability message and return a checkAvailabilityResponse or invalidDataFault message.

  • MakeReservation. To make a reservation, a client must provide a name, address, and credit card information, and the service will return a confirmation number if the reservation is successful. The service will return an error message if the credit card number or any other data field is invalid. Thus, the service will accept a makeReservation message and return a makeReservationResponse or invalidCreditCardFault message.

We know that we will later need to build a complete system that supports transactions and secured transmission, but initially we will implement only minimal functionality. In fact, to simplify our first example, we will implement only the CheckAvailability operation.

The next several sections proceed step-by-step through the process of developing a WSDL 2.0 document that describes the desired Web service. However, for those who can't wait to see a complete example, here is the WSDL 2.0 document that we'll be creating.

Example 2-1. WSDL 2.0 Document for the GreatH Web Service (Initial Example)

<?xml version="1.0" encoding="utf-8" ?> 
<description 
    xmlns="http://www.w3.org/2005/05/wsdl"
    targetNamespace= "http://greath.example.com/2004/wsdl/resSvc" 
    xmlns:tns= "http://greath.example.com/2004/wsdl/resSvc"
    xmlns:ghns = "http://greath.example.com/2004/schemas/resSvc"
    xmlns:wsoap= "http://www.w3.org/2005/05/wsdl/soap"
    xmlns:soap="http://www.w3.org/2003/05/soap-envelope">

  <documentation>
    This document describes the GreatH Web service.  Additional 
    application-level requirements for use of this service -- 
    beyond what WSDL 2.0 is able to describe -- are available 
    at http://greath.example.com/2004/reservation-documentation.html
  </documentation>

  <types>
    <xs:schema 
        xmlns:xs="http://www.w3.org/2001/XMLSchema"
        targetNamespace="http://greath.example.com/2004/schemas/resSvc"
        xmlns="http://greath.example.com/2004/schemas/resSvc">

      <xs:element name="checkAvailability" type="tCheckAvailability"/>    
      <xs:complexType name="tCheckAvailability">     
        <xs:sequence>      
          <xs:element  name="checkInDate" type="xs:date"/>      
          <xs:element  name="checkOutDate" type="xs:date"/>      
          <xs:element  name="roomType" type="xs:string"/>      
        </xs:sequence>     
      </xs:complexType>   
            
      <xs:element name="checkAvailabilityResponse" type="xs:double"/>    
    
      <xs:element name="invalidDataError" type="xs:string"/>    

    </xs:schema>    
  </types>
  
  <interface  name = "reservationInterface" >

    <fault name = "invalidDataFault"
            element = "ghns:invalidDataError"/> 
   
    <operation name="opCheckAvailability" 
            pattern="http://www.w3.org/2005/05/wsdl/in-out" 
            style="http://www.w3.org/2005/05/wsdl/style/uri"
            safe = "true">
        <input messageLabel="In" 
              element="ghns:checkAvailability" />
        <output messageLabel="Out" 
              element="ghns:checkAvailabilityResponse" />
        <outfault ref="tns:invalidDataFault" messageLabel="Out"/>
    </operation>

  </interface>

  <binding name="reservationSOAPBinding" 
          interface="tns:reservationInterface"
          type="http://www.w3.org/2005/05/wsdl/soap"
          wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP">
 
    <fault ref="tns:invalidDataFault" 
      wsoap:code="soap:Sender"/>

    <operation ref="tns:opCheckAvailability" 
      wsoap:mep="http://www.w3.org/2003/05/soap/mep/soap-response"/>

  </binding>

  <service name="reservationService" 
       interface="tns:reservationInterface">

     <endpoint name="reservationEndpoint" 
               binding="tns:reservationSOAPBinding"
               address ="http://greath.example.com/2004/reservation"/>
        
  </service>

</description>

2.2 Getting Started: Defining a WSDL Target Namespace

Before writing our WSDL 2.0 document, we need to decide on a WSDL target namespace URI for it. The WSDL target namespace is analogous to an XML Schema target namespace: interface, binding and service names that we define in our WSDL document will be associated with the WSDL target namespace, and thus will be distinguishable from similar names in a different WSDL target namespace. (This will become important if using WSDL 2.0's import or interface inheritance mechanisms.)

The value of the WSDL target namespace MUST be an absolute URI. Furthermore, it SHOULD be dereferenceable to a WSDL 2.0document that describes the Web service that the WSDL target namespace is used to describe. For example, the GreatH owners SHOULD make the WSDL document available from this URI. (And if a WSDL description is split into multiple documents, then the WSDL target namespace should resolve to a master document that includes all the WSDL documents needed for that service description.) However, there is no absolute requirement for this URI to be dereferenceable, so a WSDL processor must not depend on it being dereferenceable.

This recommendation may sound circular, but bear in mind that the client might have obtained the WSDL document from anywhere -- not necessarily an authoritative source. But by dereferencing the WSDL target namespace URI, a user SHOULD be able to obtain an authoritative version. Since GreatH will be the owner of the service, the WSDL target namespace URI should refer to a location on the GreatH Web site or otherwise within its control.

Once we have decided on a WSDL target namespace URI, we can begin our WSDL 2.0 document as the following empty shell.

Example 2-2. An Initial Empty WSDL 2.0 Document

<?xml version="1.0" encoding="utf-8" ?> 
<description 
    xmlns="http://www.w3.org/2005/05/wsdl"
    targetNamespace= "http://greath.example.com/2004/wsdl/resSvc" 
    xmlns:tns= "http://greath.example.com/2004/wsdl/resSvc"
    . . . >

  . . .
</description>

2.2.1 Explanation of Example

<description

Every WSDL 2.0 document has a description element as its top-most element. This merely acts as a container for the rest of the WSDL 2.0 document, and is used to declare namespaces that will be used throughout the document.

xmlns="http://www.w3.org/2005/05/wsdl"

This is the XML namespace for WSDL 2.0 itself. Because we have not defined a prefix for it, any unprefixed elements or attributes are expected to be WSDL 2.0 elements or attributes (such as the description element).

targetNamespace= "http://greath.example.com/2004/wsdl/resSvc"

This defines the WSDL target namespace that we have chosen for the GreatH reservation service, as described above. Note that this is not an actual XML namespace declaration. Rather, it is a WSDL 2.0 attribute whose purpose is analogous to an XML Schema target namespace.

xmlns:tns= "http://greath.example.com/2004/wsdl/resSvc"

This is an actual XML namespace declaration for use in our GreatH service description. Note that this is the same URI that was specified above as the value of the targetNamespace attribute. This will allow us later to use the tns: prefix in QNames, to refer to the WSDL target namespace of the GreatH service. (For more on QNames see [XML Namespaces] section 3 Qualified Names.)

Now we can start describing the GreatH service.

2.3 Defining Message Types

We know that the GreatH service will be sending and receiving messages, so a good starting point in describing the service is to define the message types that the service will use. We'll use XML Schema to do so, because WSDL 2.0 WSDL processors are likely to support XML Schema at a minimum. However, WSDL 2.0 does not prohibit the use of some other schema definition language.

WSDL 2.0 allows message types to be defined directly within the WSDL document, inside the types element, which is a child of the description element. (Later we'll see how we can provide the type definitions in a separate document, using XML Schema's import mechanism.) The following schema defines checkAvailability, checkAvailabilityResponse and invalidDataError message types that we'll need.

In WSDL 2.0, all normal and fault message types must be defined as single elements at the topmost level (though of course each element may have any amount of substructure inside it). Thus, a message type must not directly consist of a sequence of elements or other complex type.

Example 2-3. GreatH Message Types

<?xml version="1.0" encoding="utf-8" ?> 
<description 
    xmlns="http://www.w3.org/2005/05/wsdl"
    targetNamespace= "http://greath.example.com/2004/wsdl/resSvc" 
    xmlns:tns= "http://greath.example.com/2004/wsdl/resSvc"
    xmlns:ghns = "http://greath.example.com/2004/schemas/resSvc"
    . . . >

  ...

  <types>
    <xs:schema 
        xmlns:xs="http://www.w3.org/2001/XMLSchema"
        targetNamespace="http://greath.example.com/2004/schemas/resSvc"
        xmlns="http://greath.example.com/2004/schemas/resSvc">

      <xs:element name="checkAvailability" type="tCheckAvailability"/>    
      <xs:complexType name="tCheckAvailability">     
        <xs:sequence>      
          <xs:element  name="checkInDate" type="xs:date"/>      
          <xs:element  name="checkOutDate" type="xs:date"/>      
          <xs:element  name="roomType" type="xs:string"/>      
        </xs:sequence>     
      </xs:complexType>   
            
      <xs:element name="checkAvailabilityResponse" type="xs:double"/>    
    
      <xs:element name="invalidDataError" type="xs:string"/>    

    </xs:schema>    
  </types>
  . . .
</description>

2.3.1 Explanation of Example

xmlns:ghns = "http://greath.example.com/2004/schemas/resSvc"

We've added another namespace declaration. The ghns namespace prefix will allow us (later, when defining an interface) to reference the XML Schema target namespace that we define for our message types. Thus, the URI we specify must be the same as the URI that we define as the target namespace of our XML Schema types (below) -- not the target namespace of the WSDL document itself.

targetNamespace="http://greath.example.com/2004/schemas/resSvc"

This is the XML Schema target namespace that we've created for use by the GreatH reservation service. The checkAvailability, checkAvailabilityResponse and invalidDataError element names will be associated with this XML Schema target namespace.

checkAvailability, checkAvailabilityResponse and invalidDataError

These are the message types that we'll use. Note that these are defined to be XML elements, as explained above.

Although we have defined several types, we have not yet indicated which ones are to be used as message types for a Web service. We'll do that in the next section.

2.4 Defining an Interface

WSDL 2.0 enables one to separate the description of a Web service's abstract functionality from the concrete details of how and where that functionality is offered. This separation facilitates different levels of reusability and distribution of work in the lifecycle of a Web service and the WSDL document that describes it.

A WSDL 2.0 interface defines the abstract interface of a Web service as a set of abstract operations, each operation representing a simple interaction between the client and the service. Each operation specifies the types of messages that the service can send or receive as part of that operation. Each operation also specifies a message exchange pattern that indicates the sequence in which the associated messages are to be transmitted between the parties. For example, the in-out pattern (see WSDL 2.0 Predefined Extensions [WSDL 2.0 Adjuncts] section 2.2.3 In-Out) indicates that if the client sends a message in to the service, the service will either send a reply message back out to the client (in the normal case) or it will send a fault message back to the client (in the case of an error). We will explain more about message exchange patterns in 5.4.3 Understanding Message Exchange Patterns (MEPs)

For the GreatH service, we will (initially) define an interface containing a single operation, opCheckAvailability, using the checkAvailability and checkAvailabilityResponse message types that we defined in the types section. We'll use the in-out pattern for this operation, because this is the most natural way to represent a simple request-response interaction. We could have instead (for example) defined two separate operations using the in-only and out-only patterns (see WSDL 2.0 Predefined Extensions [WSDL 2.0 Adjuncts] section 2.2.1 In-Only and section 2.2.5 Out-Only), but that would just complicate matters for the client, because we would then have to separately indicate to the client developer that the two operations should be used together as a request-response pair.

In addition to the normal input and output messages, we also need to specify the fault message that we wish to use in the event of an error. WSDL 2.0 permits fault messages to be declared within the interface element in order to facilitate reuse of faults across operations. If a fault occurs, it terminates whatever message sequence was indicated by the message exchange pattern of the operation.

Let's add these to our WSDL document.

Example 2-4. GreatH Interface Definition

<?xml version="1.0" encoding="utf-8" ?> 
<description 
    xmlns="http://www.w3.org/2005/05/wsdl"
    targetNamespace= "http://greath.example.com/2004/wsdl/resSvc" 
    xmlns:tns= "http://greath.example.com/2004/wsdl/resSvc"
    xmlns:ghns = "http://greath.example.com/2004/schemas/resSvc"
    . . . >

  . . .
  <types>
        ...
  </types>
  
  <interface  name = "reservationInterface" >

    <fault name = "invalidDataFault"
            element = "ghns:invalidDataError"/> 
   
    <operation name="opCheckAvailability" 
            pattern="http://www.w3.org/2005/05/wsdl/in-out"
            style="http://www.w3.org/2005/05/wsdl/style/uri"
            safe = "true">
        <input messageLabel="In" 
              element="ghns:checkAvailability" />
        <output messageLabel="Out" 
              element="ghns:checkAvailabilityResponse" />
        <outfault ref="tns:invalidDataFault" messageLabel="Out"/>
    </operation>

  </interface>

  . . .
</description>

2.4.1 Explanation of Example

<interface name = "reservationInterface" >

Interfaces are declared directly inside the description element. In this example, we are declaring only one interface, but in general a WSDL 2.0 document may declare more than one interface. Thus, each interface must be given a name that is unique within the set of interfaces defined in this WSDL target namespace. Interface names are tokens that must not contain a space or colon (":").

<fault name = "invalidDataFault"

The name attribute defines a name for this fault. The name is required so that when an operation is defined, it can reference the desired fault by name. Fault names must be unique within an interface.

element = "ghns:invalidDataError"/>

The element attribute specifies the schema type of the fault message, as previously defined in the types section.

<operation name="opCheckAvailability"

The name attribute defines a name for this operation, so that it can be referenced later when bindings are defined. Operation names must also be unique within an interface. (WSDL 2.0 uses separate symbol spaces for operation and fault names, so operation name "foo" is distinct from fault name "foo".)

pattern="http://www.w3.org/2005/05/wsdl/in-out"

This line specifies that this operation will use the in-out pattern as described above. WSDL 2.0 uses URIs to identify message exchange patterns in order to ensure that the identifiers are globally unambiguous, while also permitting future new patterns to be defined by anyone. (However, just because someone defines a new pattern and creates a URI to identify it, that does not mean that other WSDL processors will automatically recognize or understand that pattern. As with any other extension, it can be used among processors that do recognize and understand it.)

style="http://www.w3.org/2005/05/wsdl/style/uri"

This line indicates that the XML schema defining the input message of this operation follows a set of rules as specified in URI Style that ensures the message can be serialized as an URI.

safe="true" >

This line indicates that this operation will not obligate the client in any way, i.e., the client can safely invoke this operation without fear that it may be incurring an obligation (such as agreeing to buy something). This is further explained in 5.4 Interface Operations.

<input messageLabel="In"

The input element specifies an input message. Even though we have already specified which message exchange pattern the operation will use, a message exchange pattern represents a template for a message sequence, and in theory could consist of multiple input and/or output messages. Thus we must also indicate which potential input message in the pattern this particular input message represents. This is the purpose of the messageLabel attribute. Since the in-out pattern that we've chosen to use only has one input message, it is trivial in this case: we simply fill in the message label "In" that was defined in WSDL 2.0 Predefined Extensions [WSDL 2.0 Adjuncts] section 2.2.3 In-Out for the in-out pattern. However, if a new pattern is defined that involve multiple input messages, then the different input messages in the pattern could then be distinguished by having different labels.

element="ghns:checkAvailability" />

This specifies the message type for this input message, as defined previously in the types section.

<output messageLabel="Out" . . .

This is similar to defining an input message.

<outfault ref="tns:invalidDataFault" messageLabel="Out"/>

This associates an output fault with this operation. Faults are declared a little differently than normal messages. The ref attribute refers to the name of a previously defined fault in this interface -- not a message schema type directly. Since message exchange patterns could in general involve a sequence of several messages, a fault could potentially occur at various points within the message sequence. Because one may wish to associate a different fault with each permitted point in the sequence, the messageLabel is used to indicate the desired point for this particular fault. It does so indirectly by specifying the message that will either trigger this fault or that this fault will replace, depending on the pattern. (Some patterns use a message-triggers-fault rule; others use a fault-replaces-message rule. See WSDL 2.0 Predefined Extensions [WSDL 2.0 Adjuncts] section 2.1.2 Message Triggers Fault and section 2.1.1 Fault Replaces Message.)

Now that we've defined the abstract interface for the GreatH service, we're ready to define a binding for it.

2.5 Defining a Binding

Although we have specified what abstract messages can be exchanged with the GreatH Web service, we have not yet specified how those messages can be exchanged. This is the purpose of a binding. A binding specifies concrete message format and transmission protocol details for an interface, and must supply such details for every operation and fault in the interface.

In the general case, binding details for each operation and fault are specified using operation and fault elements inside a binding element, as shown in the example below. However, in some cases it is possible to use defaulting rules to supply the information. The WSDL 2.0 SOAP binding extension, for example, defines some defaulting rules for operations. (See Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts [WSDL 2.0 Adjuncts], Default Binding Rules.)

In order to accommodate new kinds of message formats and transmission protocols, bindings are defined using extensions to the WSDL 2.0 language, via WSDL 2.0's open content model. (See 7.1 Extensibility for more on extensibility.) WSDL 2.0 Part 2 [WSDL 2.0 Adjuncts] defines binding extensions for SOAP 1.2 [SOAP 1.2 Part 1: Messaging Framework] and HTTP 1.1 [IETF RFC 2616] as predefined extensions, so that SOAP 1.2 or HTTP 1.1 bindings can be easily defined in WSDL 2.0 documents. However, other specifications could define new binding extensions that could also be used to define bindings. (As with any extension, other WSDL processors would have to know about the new constructs in order to make use of them.)

For the GreatH service, we will use SOAP 1.2 as our concrete message format and HTTP as our underlying transmission protocol, as shown below.

Example 2-5. GreatH Binding Definition

<?xml version="1.0" encoding="utf-8" ?> 
<description 
    xmlns="http://www.w3.org/2005/05/wsdl"
    targetNamespace= "http://greath.example.com/2004/wsdl/resSvc" 
    xmlns:tns= "http://greath.example.com/2004/wsdl/resSvc"
    xmlns:ghns = "http://greath.example.com/2004/schemas/resSvc"
    xmlns:wsoap= "http://www.w3.org/2005/05/wsdl/soap"
    xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
  . . .

  <types>
    . . .
  </types>
  
  <interface  name = "reservationInterface" >
        ...
  </interface>

  <binding name="reservationSOAPBinding" 
          interface="tns:reservationInterface"
          type="http://www.w3.org/2005/05/wsdl/soap"
          wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP">

    <operation ref="tns:opCheckAvailability" 
      wsoap:mep="http://www.w3.org/2003/05/soap/mep/soap-response"/>
  
    <fault ref="tns:invalidDataFault" 
      wsoap:code="soap:Sender"/>

  </binding>

  . . .
</description>

2.5.1 Explanation of Example

xmlns:wsoap= "http://www.w3.org/2005/05/wsdl/soap"

We've added two more namespace declarations. This one is the namespace for the SOAP 1.2 binding extension that is defined in WSDL 2.0 Part 3 [SOAP 1.2 Part 1: Messaging Framework]. Elements and attributes prefixed with wsoap: are constructs defined there.

xmlns:soap="http://www.w3.org/2003/05/soap-envelope"

This namespace is defined by the SOAP 1.2 specification itself. The SOAP 1.2 specification defines certain terms within this namespace to unambiguously identify particular concepts. Thus, we will use the soap: prefix when we need to refer to one of those terms.

<binding name="reservationSOAPBinding"

Bindings are declared directly inside the description element. The name attribute defines a name for this binding. Each name must be unique among all bindings in this WSDL target namespace, and will be used later when we define a service endpoint that references this binding. WSDL 2.0 uses separate symbol spaces for interfaces, bindings and services, so interface "foo", binding "foo" and service "foo" are all distinct.

interface="tns:reservationInterface"

This is the name of the interface whose message format and transmission protocols we are specifying. As discussed in 6. More on Bindings, a reusable binding can be defined by omitting the interface attribute. Note also the use of the tns: prefix, which refers to the previously defined WSDL target namespace for this WSDL document. In this case it may seem silly to have to specify the tns: prefix, but in 7.3 Import mechanism and authoring style we will see how WSDL 2.0's import mechanism can be used to combine components that are defined in different WSDL target namespaces.

type="http://www.w3.org/2005/05/wsdl/soap"

This specifies what kind of concrete message format to use, in this case SOAP 1.2.

wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP"

This attribute is specific to WSDL 2.0's SOAP binding extension (thus it uses the wsoap: prefix). It specifies the underlying transmission protocol that should be used, in this case HTTP.

<operation ref="tns:opCheckAvailability"

This not defining a new operation; rather, it is referencing the previously defined opCheckAvailability operation in order to specify binding details for it. This element can be omitted if defaulting rules are instead used to supply the necessary information. (See the SOAP binding extension in WSDL 2.0 Part 2 [WSDL 2.0 Adjuncts] section 4.3 Default Binding Rules .)

wsoap:mep="http://www.w3.org/2003/05/soap/mep/soap-response">

This attribute is also specific to WSDL 2.0's SOAP binding extension. It specifies the SOAP message exchange pattern (MEP) that will be used to implement the abstract WSDL 2.0 message exchange pattern (in-out) that was specified when the opCheckAvailability operation was defined.

When HTTP is used as the underlying transport protocol (as in this example) the wsoap:mep attribute also controls whether GET or POST will be used as the underlying HTTP method. In this case, the use of wsoap:mep="http://www.w3.org/2003/05/soap/mep/soap-response" causes GET to be used by default. See also 6.7 HTTP GET Versus POST: Which to Use?.

<fault ref="tns:invalidDataFault"

As with a binding operation, this is not declaring a new fault; rather, it is referencing a fault (invalidDataFault) that was previously defined in the opCheckAvailability interface, in order to specify binding details for it.

wsoap:code="soap:Sender"/>

This attribute is also specific to WSDL 2.0's SOAP binding extension. This specifies the SOAP 1.2 fault code that will cause this fault message to be sent. If desired, a list of subcodes can also be specified using the optional wsoap:subcodes attribute.

2.6 Defining a Service

Now that our binding has specified how messages will be transmitted, we are ready to specify where the service can be accessed, by use of the service element.

A WSDL 2.0 service specifies a single interface that the service will support, and a list of endpoint locations where that service can be accessed. Each endpoint must also reference a previously defined binding to indicate what protocols and transmission formats are to be used at that endpoint. A service is only permitted to have one interface. (See 7.4 Multiple Interfaces for the Same Service for further discussion of this limitation.)

Here is a definition for our GreatH service.

Example 2-6. GreatH Service Definition

<?xml version="1.0" encoding="utf-8" ?> 
<description 
    xmlns="http://www.w3.org/2005/05/wsdl"
    targetNamespace= "http://greath.example.com/2004/wsdl/resSvc" 
    xmlns:tns= "http://greath.example.com/2004/wsdl/resSvc"
    xmlns:ghns = "http://greath.example.com/2004/schemas/resSvc"
    xmlns:wsoap= "http://www.w3.org/2005/05/wsdl/soap"
    xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
  . . .

  <types>
    . . .
  </types>
  
  <interface  name = "reservationInterface" >
    . . .
  </interface>

  <binding name="reservationSOAPBinding" 
          interface="tns:reservationInterface"
        . . . >
    . . .
  </binding>

  <service name="reservationService" 
       interface="tns:reservationInterface">

     <endpoint name="reservationEndpoint" 
               binding="tns:reservationSOAPBinding"
               address ="http://greath.example.com/2004/reservation"/>
        
  </service>
  
</description>

2.6.1 Explanation of Example

<service name="reservationService"

This defines a name for this service, which must be unique among service names in the WSDL target namespace. The name attribute is required. It allows URIs to be created that identify components in WSDL 2.0 description. (See WSDL 2.0 Core Language [WSDL 2.0 Core Language] appendix C URI References for WSDL constructs.)

interface="tns:reservationInterface">

This specifies the name of the previously defined interface that these service endpoints will support.

<endpoint name="reservationEndpoint"

This defines an endpoint for the service, and a name for this endpoint, which must be unique within this service.

binding="tns:reservationSOAPBinding"

This specifies the name of the previously defined binding to be used by this endpoint.

address ="http://greath.example.com/2004/reservation"/>

This specifies the physical address at which this service can be accessed using the binding specified by the binding attribute.

That's it! Well, almost.

2.7 Documenting the Service

As we have seen, a WSDL 2.0 document is inherently only a partial description of a service. Although it captures the basic mechanics of interacting with the service -- the message types, transmission protocols, service location, etc. -- in general, additional documentation will need to explain other application-level requirements for its use. For example, such documentation should explain the purpose and use of the service, the meanings of all messages, constraints on their use, and the sequence in which operations should be invoked.

The documentation element allows the WSDL author to include some human-readable documentation inside a WSDL 2.0 document. It is also a convenient place to reference any additional external documentation that a client developer may need in order to use the service. It can appear in a number of places in a WSDL 2.0 document (see 3.1 WSDL 2.0 Infoset), though in this example we have only demonstrated its use at the beginning.

Example 2-7. Documenting the GreatH Service

<?xml version="1.0" encoding="utf-8" ?> 
<description 
    . . . >

  <documentation>
    This document describes the GreatH Web service.  Additional 
    application-level requirements for use of this service -- 
    beyond what WSDL 2.0 is able to describe -- are available 
    at http://greath.example.com/2004/reservation-documentation.html
  </documentation>
  . . .  
</description>

2.7.1 Explanation of Example

<documentation>

This element is optional, but a good idea to include. It can contain arbitrary mixed content.

at http://greath.example.com/2004/reservation-documentation.html

The most important thing to include is a pointer to any additional documentation that a client developer would need in order to use the service.

This completes our presentation of the GreatH example.

3. WSDL 2.0 Infoset, Schema and Component Model

In computer science theory, a language consists of a (possibly infinite) set of sentences, and each sentence is a finite string of literal symbols or characters. A language specification must therefore define the set sentences in that language, and, to be useful, it should also indicate the meaning of each sentence. Indeed, this is the purpose of the WSDL 2.0 specification.

However, instead of defining WSDL 2.0 in terms of literal symbols or characters, to avoid dependency on any particular character encoding, WSDL 2.0 is defined in terms of the XML Infoset [XML Information Set]. Specifically, a WSDL 2.0 document consists of a description element information item (in the XML Infoset) that conforms to the WSDL 2.0 specification. In other words, a sentence in the WSDL 2.0 language is a description element information item that obeys the additional constraints spelled out in the WSDL 2.0 specification.

Since an XML Infoset can be created from more than one physical document, a WSDL 2.0 document does not necessarily correspond to a single physical document: the word "document" is used figuratively, for convenience. Furthermore, since WSDL 2.0 provides import and include mechanisms, a WSDL 2.0 document may reference other WSDL 2.0 documents to facilitate convenient organization or reuse. In such cases, the meaning of the including or importing document as a whole will depend (in part) on the meaning of the included or imported document.

The XML Infoset uses terms like "element information item" and "attribute information item". Unfortunately, those terms are rather lengthy to repeat often. Thus, for convenience, this primer often uses the terms "element" and "attribute" instead, as a shorthand. It should be understood, however, that since WSDL 2.0 is based on the XML Infoset, we really mean "element information item" and "attribute information item", respectively.

3.1 WSDL 2.0 Infoset

The following diagram gives an overview of the XML Infoset for a WSDL 2.0 document.


WSDL 2.0 Infoset Diagram

Figure 3-1. WSDL 2.0 Infoset Diagram


3.2 WSDL 2.0 Schema and Element Ordering

The WSDL 2.0 specification supplies a normative WSDL 2.0 schema, defined in XML Schema [XML Schema: Structures] [XML Schema: Datatypes], which can be used as an aid in validating WSDL 2.0 documents.

Editorial note: KevinL 20050428
ToDo: update link to wsdl2.0 schema when final uri is available
Although the WSDL 2.0 schema does not indicate the required ordering of elements, the WSDL 2.0 specification (WSDL 2.0 Part 1 [WSDL 2.0 Core Language] "XML Representation of Description Component") clearly states a set of constraints about how the children elements of the description element should be ordered. Thus, the order of the WSDL 2.0 elements matters, in spite of what the WSDL 2.0 schema says.

The following is a pseudo-content model of description.

<description>
  <documentation />?
  [ <import /> | <include /> ]*
  <types />?
  [ <interface /> | <binding /> | <service /> ]*
</description>

In other words, the children elements of the description element should be ordered as follows:

  • An optional documentation comes first, if present.

  • then comes zero or more elements from among the following, in any order:

    • Zero or more include

    • Zero or more import

    • Zero or more extensions

  • An optional types follows

  • Zero or more elements from among the following, in any order:

    • interface elements

    • binding elements

    • service elements

    • Zero or more extensions.

Note the term "extension" is used above as a convenient way to refer to namespace-qualified extension elements. The namespace name of such extension elements must not be"http://www.w3.org/2005/05/wsdl".

3.3 WSDL 2.0 Component Model

The WSDL 2.0 Infoset model above illustrates the required structure of a WSDL 2.0 document, using the XML Infoset. However, the WSDL 2.0 language also imposes many semantic constraints over and above structural conformance to this XML Infoset. In order to precisely describe these constraints, and as an aid in precisely defining the meaning of each WSDL 2.0 document, the WSDL 2.0 specification defines a component model as an additional layer of abstraction above the XML Infoset. Constraints and meaning are defined in terms of this component model, and the definition of each component includes a mapping that specifies how values in the component model are derived from corresponding items in the XML Infoset. The following diagram gives an overview of the WSDL 2.0 components and their containment hiearchy.


WSDL 2.0 Components Containment Hiearchy

Figure 3-2. WSDL 2.0 Components Containment Hiearchy


In general, the WSDL 2.0 component model parallels the structure of the required XML Infoset illustrated above. For example, the Description, Interface, Binding, Service and Endpoint components correspond to the description, interface, binding, service, and endpoint element information items, respectively. Since WSDL 2.0 relies heavily on the component model to convey the meaning of the constructs in the WSDL 2.0 language, you can think of the Description component as representing the meaning of the description element information item, and hence, it represents the meaning of the WSDL 2.0 document as a whole.

Furthermore, each of these components has properties whose values are (usually) derived from the element and attribute information item children of those element information items. For example, the Service component corresponds to the service element information item, so the Service component has an {endpoints} property whose value is a set of Endpoint components corresponding to the endpoint element information item children of that service element information item. (Whew!).

The WSDL 2.0 component model is particularly helpful in defining the meaning of import and include. WSDL 2.0 include allows components from another WSDL 2.0 document having the same targetNamespace to be merged in with the components of the current WSDL 2.0 document, and is transitive (i.e., if the included document also includes a WSDL 2.0 document, then those components will also be merged, and so on). WSDL 2.0 import allows components from another WSDL 2.0 document having a different targetNamespace to be merged in with comonents of the current WSDL 2.0 document, and is not transitive.

4. More on Message Types

The WSDL 2.0 types element provides a mechanism for enclosing message schemas in a WSDL 2.0 document. Because WSDL 2.0 directly supports schemas written in XML Schema [XML Schema: Structures], we will focus here on the use of XML Schema to define message types. Schemas written in other type definition languages must be defined using a WSDL 2.0 language extension. For examples of other schema languages, see WSDL 2.0 Part 1 [WSDL 2.0 Core Language] Appendix E "Examples of Specifications of Extension Elements for Alternative Schema Language Support. (Non-Normative)".

Editorial note: dbooth 2005-04-13
ToDo: Update the above reference to appendix E, as the WG decided to move it to a separate document.
Editorial note: dbooth 2005-04-13
ToDo: Check the sections below on import and include mechanisms for correctness. (Be sure to check the table also.) I'm not sure I got them all right.

There are two ways to indicate XML Schema message definitions using the types element. One way is to embed schema definitions within xs:schema elements that are children of types, as we have already seen. The other way is to use xs:import directly under types. It is perfectly reasonable to use both ways in one WSDL document.

A WSDL description MUST NOT refer to XML Schema components that are neither imported nor embedded into that WSDL description. In other words, the use of xs:import and/or xs:schema is a necessary condition for making XML Schema components available to a WSDL Description component.

The following XML syntax for the types element illustrates the use of xs:import and xs:schema:

<description>
<types>
<documentation />?
<xs:import namespace="xs:anyURI" schemaLocation= "xs:anyURI"?/>*
<xs:schema targetNamespace="xs:anyURI" />*

[extension elements]*
</types>
</description>

4.1 Embedding XML Schema

We have already seen an example of using embedded schema definitions in section 2.3 Defining Message Types, so we will merely add a few additional points here.

When XML Schema is embedded directly in a WSDL 2.0 document, it uses the existing top-level xs:schema element defined by XML Schema [XML Schema: Structures] to do so, as though the schema had been copied and pasted into the types element. The schema components defined in the embedded schema are then available to WSDL for reference by QName (see WSDL 2.0 Part 1 [WSDL 2.0 Core Language] "QName Resolution").

Although WSDL 2.0 provides a wsdl:import mechanism (described in the next section), an embedded XML schema may also use XML Schema's native xs:import and xs:include elements to refer to schemas either in separate files or embedded in the same WSDL 2.0 document. However, components embedded using xs:import have different visibility from those embedded using xs:include: xs:included components are available to WSDL for reference by QName, but xs:imported components are not.

4.2 Importing XML Schema

There are many cases where one would prefer importing schema definitions from separate schema files instead of embedding them directly under the types element. One reason is reusability of the schemas. Although WSDL 2.0 provides a wsdl:import mechanism, type and element declarations embedded in a WSDL 2.0 document are NOT automatically made available to the importing document, even though other WSDL 2.0 components (such as Interfaces, Bindings, etc.) do become available. Therefore, if you wish to share schema documents across several WSDL 2.0 documents, they should instead be placed in separate XML Schema documents and imported into each WSDL 2.0 document using xs:import directly under types.

The xs:import mechanism is not transitive. Only components defined in the imported schema itself and components the schema includes via xs:include are available to the containing WSDL document. Specifically, components that the schema imports via xs:import are NOT available to WSDL.

Editorial note: dbooth 2005-04-13
Check this. An issue was recently raised about import not being transitive.

Here is an example of importing a schema. Assuming the message types in Example 2-3 are defined in a separate schema file named "http://greath.example.com/2004/schemas/resSvc.xsd" with a target namespace "http://greath.example.com/2004/schemas/resSvc", the schema definition can then be imported into the WSDL as follows:

Example 4-1. Example of Importing Message Definitions

<?xml version="1.0" encoding="utf-8" ?> 
<description 
xmlns="http://www.w3.org/2005/05/wsdl"
targetNamespace= "http://greath.example.com/2004/wsdl/resSvc" 
xmlns:tns= "http://greath.example.com/2004/wsdl/resSvc"
xmlns:ghns = "http://greath.example.com/2004/schemas/resSvc"
. . . >
. . .

<types>
<xs:import namespace="http://greath.example.com/2004/schemas/resSvc" 
schemaLocation= "http://greath.example.com/2004/schemas/resSvc.xsd"/>  
</types>

. . .
</description>

4.3 Summary of Import and Include Mechanisms

The following table summarizes the similarities and differences between the wsdl: and xs: include and import mechanisms.


Table 4-1. Summary of Import and Include Mechanisms
Mechanism Imported/Included Document Type Meaning Transitive?
wsdl:import WSDL 2.0 document Merge Interface, Binding and Service components from another WSDL 2.0 document that has a DIFFERENT targetNamespace. (Schema type and element declarations are NOT merged.) No
wsdl:include WSDL 2.0 document Merge Interface, Binding and Service components from another WSDL 2.0 document that has the SAME targetNamespace. (Schema type and element declarations are NOT merged.) Yes
xs::import XML Schema document Merge type and element declarations from another XML Schema document that has a DIFFERENT targetNamespace. No
xs:import XML Schema document Merge type and element declarations from another XML Schema document that has the SAME targetNamespace. Yes

More advanced topics on importing schemas are discussed in 7.10 Importing Schemas

5. More on Interfaces

We previously mentioned that a WSDL 2.0 interface is basically a set of operations. However, there are some additional capabilities that we have not yet covered. First, let's review the syntax for the interface element.

5.1 Interface Syntax

Below is the XML syntax summary of the interface element, simplified by omitting optional <documentation> elements and <feature> and <property> extension elements:

<description targetNamespace="xs:anyURI" >

  . . .
  <interface name="xs:NCName" 
          extends="list of xs:QName"? 
          styleDefault="list of xs:anyURI"? >

    <fault name="xs:NCName" 
                 element="xs:QName"? >
    </fault>*

    <operation name="xs:NCName" 
            pattern="xs:anyURI" 
            style="list of xs:anyURI"? 
            safe="xs:boolean"? >

      <input messageLabel="xs:NCName"? 
                        element="union of xs:QName, xs:Token"? >
      </input>*

      <output messageLabel="xs:NCName"? 
                        element="union of xs:QName, xs:Token"? >
      </output>*

      <infault ref="xs:QName" messageLabel="xs:NCName"? > </infault>*

      <outfault ref="xs:QName" messageLabel="xs:NCName"? > </outfault>*

    </operation>*

  </interface>*
  . . .

</description>
  

The interface element has two optional attributes: styleDefault and extends . The styleDefault attribute can be used to define a default value for the style attributes of all operations under this interface (see WSDL 2.0 Part 1 "styleDefault attribute information item"). The extends attribute is for inheritance, and is explained next.

5.2 Interface Inheritance

The optional extends attribute allows an interface to extend or inherit from one or more other interfaces. In such cases the interface contains the operations of the interfaces it extends, along with any operations it defines directly. Two things about extending interfaces deserve some attention.

First, an inheritance loop (or infinite recursion) is prohibited: the interfaces that a given interface extends MUST NOT themselves extend that interface either directly or indirectly.

Second, we must explain what happens when operations from two different interfaces have the same target namespace and operation name. There are two cases: either the component models of the operations are the same, or they are different. If the component models are the same (per the component comparison algorithm defined in WSDL 2.0 Part 1 [WSDL 2.0 Core Language] "Equivalence of Components") then they are considered to be the same operation, i.e., they are collapsed into a single operation, and the fact that they were included more than once is not considered an error. (For operations, component equivalence basically means that the two operations have the same set of attributes and descendents.) In the second case, if two operations have the same name in the same WSDL target namespace but are not equivalent, then it is an error. For the above reason, it is considered good practice to ensure that all operations within the same target namespace are named uniquely.

Finally, since faults, features and properties can also be defined as children of the interface element (as described in the following sections), the same name-collision rules apply to those constructs.

Let's say the GreatH hotel wants to maintain a a standard message log operation for all received messages. It wants this operation to be reusable across the whole reservation system, so each service will send out, for potential use of a logging service, the content of of each message it receives together with a timestamp and the originator of the message. One way to meet such requirement is to define the log operation in an interface which can be inherited by other interfaces. Assuming a messageLog element is already defined in the ghns namespace with the required content, the inheritance use case is illustrated in the following example. As a result of the inheritance, the reservationInterface now contains two operations: opCheckAvailability and opLogMessage

Example 5-1. Interface Inheritance

                                        
<description ...>
        ...
        <interface  name = "messageLogInterface" >
                                
                <operation name="opLogMessage" 
                                pattern="http://www.w3.org/2005/05/wsdl/out-only">
                        <output messageLabel="out" 
                                element="ghns:messageLog" />
                </operation>

        </interface>

        <interface  name="reservationInterface" extends="tns:messageLogInterface" >
   
                <operation name="opCheckAvailability" 
                                pattern="http://www.w3.org/2005/05/wsdl/in-out"
                                style="http://www.w3.org/2005/05/wsdl/style/uri"
                                safe = "true">
                        <input messageLabel="In" 
                                element="ghns:checkAvailability" />
                        <output messageLabel="Out" 
                                element="ghns:checkAvailabilityResponse" />
                        <outfault ref="tns:invalidDataFault" messageLabel="Out"/>

                </operation>
        </interface>
        ...
</description>

Now let's have a look at the element children of interface, beginning with fault.

5.3 Interface Faults

The fault element is used to declare faults that may occur during execution of operations of an interface. They are declared directly under interface, and referenced from operations where they apply, in order to permit reuse across multiple operations.

Faults are very similar to messages and can be viewed as a special kind of message. Both faults and messages may carry a payload that is normally described by an element declaration. However, WSDL treats faults and messages slightly differently. The messages of an operation directly refer to their element declaration, however the faults of an operation indirectly refer to their element declaration via a fault element that is defined on the interface.

The reason for defining faults at the interface level is to allow their reuse across multiple operations. This design is especially beneficial when bindings are defined, since in binding extensions like SOAP there is additional information that is associated with faults. In the case of SOAP, faults have codes and subcodes in addition to a payload. By defining faults at the interface level, common codes and subcodes can be associated with them, thereby ensuring consistency across all operations that use the faults

The fault element has a required name attribute that must be unique within the WSDL document's target namespace, and permits it to be referenced from operation declarations. The optional element attribute can be used to indicate a schema for the content or payload of the fault message. Its value should be the QName of a global element defined in the types section. Please note when other type systems are used to define the schema for a fault message, additional attributes may need to be defined via WSDL's attribute extension mechanism to allow the schema to be associated with the fault.

5.4 Interface Operations

As shown earlier, the operation element is used to indicate an operation supported by the containing interface. It associates message schemas with a message exchange pattern (MEP), in order to abstractly describe a simple interaction with a Web service.

5.4.1 Operation Attributes

An operation has two required and two optional attributes:

  • A required name attribute, as seen already, which must be unique within the interface.

  • A required pattern attribute whose value must be an absolute URI that identifies the desired MEP for the operation. MEPs are further explained in 5.4.3 Understanding Message Exchange Patterns (MEPs).

  • An optional style attribute whose value is a list of absolute URIs. Each URI identifies a certain set of rules that were followed in defining this operation. It is an error if a particular style is indicated, but the associated rules are not followed. [WSDL 2.0 Adjuncts] defines a set of styles, including

    • RPC Style.The RPC style is selected when the style is assigned the value http://www.w3.org/2005/05/wsdl/style/rpc. It places restrictions for Remote Procedure Call-types of interactions.

    • URI Style. The URI style is selected when the style is assigned the value http://www.w3.org/2005/05/wsdl/style/uri. It places restrictions on message definitions so they may be serialized into something like HTTP URL encoded.

    • The Multipart style. The Multipart style is selected when the style is assigned the value http://www.w3.org/2005/05/wsdl/style/multipart. In http binding, for Xform clients, an message must be defined following the Multipart style and serialized as "Multipart/form-data".

    You can find more details of these WSDL 2.0 predefined styles. Section 7.7 RPC Style provides an example of using the RPC style. [WSDL 2.0 Adjuncts] provides examples for the URI style and Multipart style.

  • An optional safety attribute whose value is a boolean indicating whether the operation is asserted to be "safe" (as defined in Section 3.5 of the Web Architecture [Web Architecture]) for clients to invoke. In essence, a safe operation is any operation that does not give the client any new obligations. For example, an operation that permits the client to check prices on products typically would not obligate the client to buy those products, and thus would be safe, whereas an operation for purchasing products would obligate the client to pay for the products that were ordered, and thus would not be safe.

    An operation SHOULD be marked safe (by setting the safety to true) if it meets the criteria for a safe interaction defined in Section 3.5 of the Web Architecture [Web Architecture], because this permits the infrastructure to perform efficiency optimizations, such as pre-fetch, re-fetch and caching.

    The default value of this attribute is false. If it is false or is not set, then no assertion is made about the safety of the operation; thus the operation MAY or MAY NOT be safe.

5.4.2 Operation Message References

An operation will also have input, output,infault, and/or outfault element children that specify the ordinary and fault message types to be used by that operation. The MEP specified by the pattern attribute determines which of these elements should be included, since each MEP has placeholders for the message types involved in its pattern.

Since operations were already discussed in 2.4 Defining an Interface, this section will merely comment on additional capabilities that were not previously explained.

5.4.2.1 The messageLabel Attribute

The messageLabel attribute of the input and output elements is optional: it is not necessary to explicitly set the messageLabel when the MEP in use is one of the eight MEPs predefined in WSDL 2.0 Part 2 [WSDL 2.0 Adjuncts] and it has only one message with a given direction.

5.4.2.2 The element Attribute

The element attribute of the input and output elements is used to specify the message content schema (a/k/a payload schema) when the content model is defined using XML Schema. As we have seen already, it can specify the QName of an element schema that was defined in the types section. However, alternatively it can specify one of the following tokens:

#any

The message content is any single element.

#none

There is no message content, i.e., the message payload is empty.

The element attribute is also optional. If it is not specified, then @@@@.

Editorial note  
ToDo: Say what happens if the element attribute is not specified, after issue LC99 is resolved. See http://www.w3.org/2002/ws/desc/4/lc-issues/issues.html#LC99
5.4.2.3 Multiple infault or outfault Elements

When infault and/or outfault occur multiple times within an operation, they define alternative fault messages.

5.4.3 Understanding Message Exchange Patterns (MEPs)

WSDL 2.0 message exchange patterns (MEPs) are used to define the sequence and cardinality of the abstract messages in an operation. By design, WSDL 2.0 MEPs are abstract. First of all, they abstract out specific message types. MEPs identify placeholders for messages, and placeholders are associated with specific message types when an operation is defined, which includes specifying which MEP to use for that operation. Secondly, unless explicitly stated otherwise, MEPs also abstract out binding-specific information like timing between messages, whether the pattern is synchronous or asynchronous, and whether the messages are sent over a single or multiple channels.

It's worth pointing out that WSDL MEPs do not exhaustively describe the set of messages that may be exchanged between a service and other nodes. By some prior agreement, another node and/or the service may send other messages (to each other or to other nodes) that are not described by the MEP. For instance, even though an MEP may define a single message sent from a service to one other node, a service defined by that MEP may multicast that message to other nodes. To maximize reuse, WSDL message exchange patterns identify a minimal contract between other parties and Web Services, and contain only information that is relevant to both the Web service and the client that engages that service.

A total of 8 MEPs are defined in [WSDL 2.0 Adjuncts]. Hopefully, these MEPs will cover the most common use cases, but they are not meant to be an exhaustive list of MEPs that can ever be used by operations. More MEPs can be defined for particular application needs by interested parties. (See 5.4.4 Defining New Message Exchange Patterns (MEPs) )

For the 8 MEPs defined by WSDL 2.0, some of them are variations of others based on how faults may be generated. For example, the In-Only pattern ("http://www.w3.org/2005/05/wsdl/in-only") consists of exactly one message received by a service from some other node. No fault maybe generated. As a variation of In-Only, Robust In-Only pattern ("http://www.w3.org/2005/05/wsdl/robust-in-only") also consists of exactly one message received by a service, but in this case faults can be triggered by the message and MUST be delivered to the originator of the message. If there is no path to this node, the fault MUST be discarded. For details about the common fault generation models used by the 8 WSDL 2.0 MEPs, see [WSDL 2.0 Adjuncts].

Depends on how the first message in the MEP is initiated, the 8 WSDL MEPs may be grouped into two groups: in-bound MEPs in which case the service receives the first message in the exchange, and out-bound MEPs in which case the service sends out the first message in the exchange. (Such Grouping is only for the purpose of easy reference in this primer).

A frequently asked question about out-bound MEPs is how a service knows where to send the message. Services using out-bound MEPs are typically part of large scale integration systems that rely on mapping and routing facilities. In such systems, out-bound MEPs are useful for abstractly specifying the functionality of a service, including its requirements for potential customers, while endpoint address information can be provided at deployment or runtime by integration infrastructure. For example, the GreatH hotel reservation system may require that every time a customer interacts with the system to check availability, data about the customer must be logged by a CRM system. At design time, it's unknown which particular CRM system would be used together with the reservation system. To address this requirement, we may change the "reservationInterface" in Example 2-1 to include an out-bound logInquiry operation. This logInquiry operation advertises to potential service clients that customer data will be made available by the reservation service at run time. When the reservation service is deployed to GreatH's IT landscape, appropriate configuration time and run time infrastructure will help determine which CRM system will get the customer data and log it appropriately. It's worth noting that in addition to being used by a CRM system for customer management purpose, the same data may also be used by a system performance analysis tool for different purpose. Providing an out-bound operation in the reservation service enables loose coupling and so improves the overall GreatH IT landscape's flexibility and scalability.

Example 5-2. Use of outbound MEPs

                                        
<description ...>
        ...
        <interface  name="reservationInterface">
                ...
                <operation name="opCheckAvailability" ... >
                
                <operation name="opLogInquiry" 
                                pattern="http://www.w3.org/2005/05/wsdl/out-only">
                        <output messageLabel="Out" element="ghns:customerData" />
                </operation>

        </interface>
        ...
</description>

5.4.4 Defining New Message Exchange Patterns (MEPs)

Although the 8 MEPs defined in WSDL 2.0 Part 2 [WSDL 2.0 Adjuncts] are intended to cover most use cases, WSDL 2.0 has designed this set to be extensible. This is why MEPs are identified by URIs rather than a fixed set of tokens. Here are the general steps for defining a new MEP.

  1. Search around on the Web to see if somebody else has already defined an MEP that is close enough to what you want. If others are already using an MEP that fits your needs, it will reduce the effort required in step 4 to get other people to adopt yours.

  2. Write an HTML document that clearly defines the MEP, and publish it at a stable URL -- see purl.org, for example -- that will represent the full, formal name of the MEP, such as http://example.com/2005/ws/in-multi-out. (This is a fictitious example: "example.com" is a standard fictitious domain name. You, of course, must use an appropriate real domain and URL.)

  3. Write and publish a corresponding specification for a binding extension that implements your MEP.

  4. Publicize your new MEP and binding extension, and get others to support them in their WSDL toolkits.

Note that the above procedure does NOT cause your MEP to become automatically recognized and usable by WSDL toolkits. It simply provides a well-defined convention for naming and reusing them.

6. More on Bindings

Bindings are used to supply protocol and encoding details that specify how messages are to be sent or received. Each binding element uses a particular binding extension to specify such information. WSDL 2.0 Part 2 [WSDL 2.0 Adjuncts] defines several binding extensions that are typically used. However, binding extensions that are not defined in WSDL 2.0 Part 2 can also be used, provided that client and service toolkits support them.

Binding information must be supplied for every operation in an interface that is used in an endpoint. However, if the desired binding extension provides suitable defaulting rules, then the information will only need to be explicitly supplied at the interface level, and the defaulting rules will implicitly propagate the information to the operations of the interface. For example, see the SOAP binding extension in WSDL 2.0 Part 2 [WSDL 2.0 Adjuncts] section 4.3 Default Binding Rules.

6.1 Syntax Summary for Bindings

Since bindings are specified using extensions to the WSDL 2.0 language (i.e., binding extensions are not in the WSDL 2.0 namespace), the XML for expressing a binding will consist of a mixture of elements and attributes from WSDL 2.0 namespace and from the binding extension's namespace, using WSDL 2.0's open content model.

Here is a syntax summary for binding, simplified by omitting optional documentation, feature and property elements. Bear in mind that this syntax summary only shows the elements and attributes defined within the WSDL 2.0 namespace. When an actual binding is defined, elements and attributes from the namespace of the desired binding extension will also be intermingled as required by that particular binding extension.

<description targetNamespace="xs:anyURI" >
  . . .
  <binding name="xs:NCName" interface="xs:QName"? >

    <fault ref="xs:QName" >  </fault>*

    <operation ref="xs:QName" >
      <input messageLabel="xs:NCName"? > </input>*
      <output messageLabel="xs:NCName"? > </output>*
    </operation>*

  </binding>*
  . . .
</description>

The binding syntax parallels the syntax of interface: each interface construct has a binding counterpart. Despite this syntactic similarity, they are indeed different constructs, since they are in different symbol spaces and are designed for different purposes.

6.2 Reusable Bindings

A binding can either be reusable (applicable to any interface) or non-reusable (specified for a particular interface). Non-reusable bindings may be specified at the granularity of the interface (assuming the binding extension provides suitable defaulting rules), or on a per-operation basis if needed. A non-reusable binding was demonstrated in 2.5 Defining a Binding.

To define a reusable binding, the binding element simply omits the interface attribute and omits specifying any operation-specific and fault-specific binding details. Endpoints can later refer to a reusable binding in the same manner as for a non-reusable binding. Thus, a reusable binding becomes associated with a particular interface when it is referenced from an endpoint, because an endpoint is part of a service, and the service specifies a particular interface that it implements. Since a reusable binding does not specify an interface, reusable bindings cannot specify operation-specific details. Therefore, reusable bindings can only be defined using binding extensions that have suitable defaulting rules, such that the binding information only needs to be explicitly supplied at the interface level.

6.3 Binding Faults

A binding fault associates a concrete message format with an abstract fault of an interface. It describes how faults that occur within a message exchange of an operation will be formatted, since the fault does not occur by itself. Rather, a fault occurs as part of a message exchange specified by an interface operation and its binding counterpart, the binding operation.

A binding fault has one required ref attribute which is a reference, by QName, to an interface fault . It identifies the abstract interface fault for which binding information is being specified. Be aware that the value of ref attribute of all the faults under a binding MUST be unique. That is, one cannot define multiple bindings for the same interface fault within a given binding.

6.4 Binding Operations

A binding operation describes a concrete binding of a particular operation of an interface to a particular concrete message format. A particular operation of an interface is uniquely identified by the WSDL target namespace of the interface and the name of the operation within that interface, via the required ref attribute of binding operation. As with faults, for each operation within a binding, the value of the ref attribute MUST be unique.

6.5 The SOAP Binding Extension

The WSDL 2.0 SOAP Binding Extension (see WSDL 2.0 Part 2 [WSDL 2.0 Adjuncts]) was primarily designed to support the features of SOAP 1.2 [SOAP 1.2 Part 1: Messaging Framework]. However, for backwards compatibility, it also provides some support for SOAP 1.1 [SOAP 1.1].

An example using the WSDL 2.0 SOAP binding extension was already presented in 2.5 Defining a Binding, but some additional points are worth mentioning:

  • Because the same binding extension is used for both SOAP 1.2 and SOAP 1.1, a wsoap:version attribute is provided to allow you to indicate which version of SOAP you want. If this attribute is not specified, it defaults to SOAP 1.2.

  • The WSDL 2.0 SOAP binding extension defines a set of default rules, so that bindings can be specified at the interface level or at the operation level (or both), with the operation level taking precedence. However, it does not define default binding rules for faults. Thus, if a given interface defines any faults, then corresponding binding information must be explicitly provided for each such fault.

  • If HTTP is used as the underlying protocol, then the binding can (and should) control whether each operation will use HTTP GET or POST. (See 6.7 HTTP GET Versus POST: Which to Use?.)

Here is an example that illustrates both a SOAP 1.2 binding (as seen before) and a SOAP 1.1 binding.

Example 6-1. SOAP 1.2 and SOAP 1.1 Bindings

<?xml version="1.0" encoding="utf-8" ?> 
<description 
  xmlns="http://www.w3.org/2005/05/wsdl"
  targetNamespace="http://greath.example.com/@@@@/wsdl/resSvc.wsdl" 
  xmlns:tns="http://greath.example.com/@@@@/wsdl/resSvc.wsdl"
  xmlns:ghns="http://greath.example.com/@@@@/schemas/resSvc.xsd"
  xmlns:wsoap="http://www.w3.org/2005/05/wsdl/soap"
  xmlns:soap="http://www.w3.org/2003/05/soap-envelope"
  xmlns:soap11="http://schemas.xmlsoap.org/soap/envelope/">

 ....

  <!-- SOAP 1.2 Binding -->
  <binding name="reservationSOAPBinding" 
    interface="tns:reservationInterface"
    type="http://www.w3.org/2005/05/wsdl/soap"
    wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP">

    <operation ref="tns:opCheckAvailability" 
      wsoap:mep="http://www.w3.org/2003/05/soap/mep/request-response"/>
  
    <fault ref="tns:invalidDataFault" 
      wsoap:code="soap:Sender"/>

  </binding>
  
  <!-- SOAP 1.1 Binding -->
  <binding name="reservationSOAP11Binding" 
    interface="tns:reservationInterface"
    type="http://www.w3.org/2005/05/wsdl/soap"
    wsoap:version="1.1"
    wsoap:protocol="http://www.w3.org/2005/05/soap11/bindings/HTTP">
  
    <operation ref="tns:opCheckAvailability"/>
  
    <fault ref="tns:invalidDataFault" 
      wsoap:code="soap11:Client"/>

  </binding>


  <service name="reservationService" 
    interface="tns:reservationInterface">

    <!-- SOAP 1.2 End Point -->
    <endpoint name="reservationEndpoint" 
      binding="tns:reservationSOAPBinding"
      address="http://greath.example.com/2004/reservation"/>

    <!-- SOAP 1.1 End Point -->
    <endpoint name="reservationEndpoint2"
      binding="tns:reservationSOAP11Binding"
      address="http://greath.example.com/2004/reservation"/>
  
  </service>  
</description>

6.5.1 Explanation of Example

Most of this example is the same as previously explained in 2.5 Defining a Binding, so we'll only point out lines that are demonstrating something new.

xmlns:soap11="http://schemas.xmlsoap.org/soap/envelope/">

This is the namespace for terms defined within the SOAP 1.1 specification [SOAP 1.1].

wsoap:version="1.1"

This line indicates that this binding uses SOAP 1.1, rather than SOAP 1.2.

wsoap:protocol="http://www.w3.org/2005/05/soap11/bindings/HTTP">

This line specifies that HTTP should be used as the underlying transmission protocol. See also 6.7 HTTP GET Versus POST: Which to Use?.

wsoap:code="soap11:Client"/>

This line specifies the SOAP 1.1 fault code that will be used in transmitting invalidDataFault.

6.6 The HTTP Binding Extension

In addition to the WSDL 2.0 SOAP binding extension described above, WSDL 2.0 Part 2 [WSDL 2.0 Adjuncts] defines a binding extension for HTTP 1.1 [IETF RFC 2616] and HTTPS [IETF RFC 2818], so that these protocols can be used natively to send and receive messages, without first encoding them in SOAP.

The HTTP binding extension provides many features to control:

  • Which HTTP operation will be used. (GET, PUT, POST, DELETE, and other HTTP operations are supported.)

  • Input, output and fault serialization

  • Transfer codings

  • Authentication requirements

  • Cookies

  • HTTP over TLS (https)

As with the WSDL 2.0 SOAP binding extension, the HTTP binding extension also provides defaulting rules to permit binding information to be specified at the interface level and used by default for each operation in the affected interface, however, defaulting rules are not provided for binding faults.

Here is an example of using the HTTP binding extension to check hotel room availability at GreatH.

Example 6-2. HTTP Binding Extension

<?xml version="1.0" encoding="utf-8" ?> 
<description xmlns="http://www.w3.org/2005/05/wsdl"
      . . .
      type="http://www.w3.org/2005/05/wsdl/http"
      xmlns:whttp="http://www.w3.org/2005/05/wsdl/http" >

  . . .
  <binding name="reservationHTTPBinding"
      interface="tns:reservationInterface"
      whttp:methodDefault="GET">

    <operation ref="tns:opCheckAvailability"
      whttp:location="{checkInDate}"  />
  </binding>

  <service name="reservationService"
    interface="tns:reservationInterface">

    <!-- HTTP 1.1 GET End Point -->
    <endpoint name="reservationEndpoint"
      binding="tns:reservationHTTPBinding"
      address="http://greath.example.com/2004/"/>

  </service>
  . . .
</description>

6.6.1 Explanation of Example

Editorial note: dbooth 2005-04-15
ToDo: Check this section. I'm not sure I got it all right, particularly regarding whttp:location. Is the first sample request URI correct? Shouldn't instance data for tCheckAvailability be in the path component? What happens if a non-leaf element type is specified, such as tCheckAvailability?
type="http://www.w3.org/2005/05/wsdl/http"

This declares the binding as being an HTTP binding.

xmlns:whttp="http://www.w3.org/2005/05/wsdl/http" >

This defines the namespace prefix for elements and attributes defined by the WSDL 2.0 HTTP binding extension.

whttp:methodDefault="GET">

The default method for operations in this interface will be HTTP GET.

whttp:location="{checkInDate}" >

The whttp:location attribute specifies a pattern for serializing input message instance data into the path component of the request URI. The default binding rules for HTTP specify that the default input serialization for GET is application/x-www-form-urlencoded. Curly braces are used to specify the name of a schema type in the input message schema, which determines what input instance data will be inserted into the path component of the request URI. The curly brace-enclosed name will be replaced with instance data in constructing the path component. Remaining input instance data (not specified by whttp:location) will either be serialized into the query string portion of the URI or into the message body, as follows: if a "/" is appended to a curly brace-enclosed type name, then any remaining input message instance data will be serialized into the message body. Otherwise it will be serialized into query parameters.

Thus, in this example, each of the elements in the tCheckAvailability type will be serialized into the query parameters. A sample resulting URI for would therefore be http://greath.example.com/2004/5-5-5?checkOutDate=6-6-5&roomType=foo.

Here is an alternate example that serializes appends "/" to the type name in order to serialize the remaining instance data into the message body:

Example 6-3. Serializing a Subset of Types in the Path


. . .
<operation ref="tns:opCheckAvailability"
    whttp:location="bycheckInDate/{checkInDate/}"  >
. . .

This would instead serialize to a request URI such as: http://greath.example.com/2004/bycheckInDate/5-5-5

6.7 HTTP GET Versus POST: Which to Use?

When a binding using HTTP is specified for an operation, the WSDL 2.0 author must decide which HTTP method is appropriate to use -- usually a choice between GET and POST. In the context of the Web as a whole (rather than specifically Web services), the W3C Technical Architecture Group (TAG) has addressed the question of when it is appropriate to use GET, versus when to use POST, in a finding entitled URIs, Addressability, and the use of HTTP GET and POST ([W3C TAG Finding: Use of HTTP GET]). From the abstract:

". . . designers should adopt [GET] for safe operations such as simple queries. POST is appropriate for other types of applications where a user request has the potential to change the state of the resource (or of related resources). The finding explains how to choose between HTTP GET and POST for an application taking into account architectural, security, and practical considerations."

Recall that the concept of a safe operation was discussed in 5.4.1 Operation Attributes. (Briefly, a safe operation is one that does not cause the invoker to incur new obligations.) Although the safe attribute of an interface operation indicates that the abstract operation is safe, it does not automatically cause GET to be used at the HTTP level when the binding is specified. The choice of GET or POST is determined at the binding level:

  • If the WSDL 2.0 SOAP binding extension is used (6.5 The SOAP Binding Extension), with HTTP as the underlying transport protocol, then GET may be specified by setting:

    wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP"

    on the binding element (to indicate the use of HTTP as the underlying protocol); and

    wsoap:mep="http://www.w3.org/2003/05/soap/mep/soap-response/"

    on the binding operation element, which causes GET to be used by default.

  • If the WSDL 2.0 HTTP binding extension is used directly (6.6 The HTTP Binding Extension), GET may be specified by setting either:

    whttp:methodDefault="GET"

    on the binding element; or

    whttp:method="GET"

    on the binding operation element, which overrides whttp:methodDefault if set on the binding element.

7. Advanced Topics

7.1 Extensibility

WSDL 2.0 provides two extensibility mechanisms: an open content model, which allows XML elements and attributes from other (non-WSDL 2.0) XML namespaces to be interspersed in a WSDL 2.0 document; and Features and Properties. Both mechanisms use URIs to identify the semantics of the extensions. For extension XML elements and attributes, the namespace URI of the extension element or attribute acts as an unambiguous name for the semantics of that extension. For Features and Properties, the Feature or Property is named by a URI.

In either case, the URI that identifies the semantics of an extension SHOULD be dereferenceable to a document that describes the semantics of that extension. As of this writing, there is no generally accepted standard for what kind of document that should be. However, the W3C TAG has been discussing the issue (see TAG issue namespaceDocument-8) and is likely to provide guidance at some point.

7.1.1 Optional Versus Required Extensions

Extensions can either be required or optional.

An optional extension is one that the client may either engage or ignore, entirely at its discretion, and is signaled by attribute wsdl:required="false" or the absence of the wsdl:required attribute (because it defaults to false). Thus, a WSDL processor, acting on behalf of the client, that encounters an unknown optional extension can safely ignore it and continue to process the WSDL 2.0 document. However, it is important to stress that optional extensions are only optional to the client -- not the service. A service MUST support all optional and required extensions that it advertises in its WSDL 2.0 document.

A required extension is one that MUST be supported and engaged by the client in order for the interaction to procede properly, and is signaled by attribute wsdl:required="true". If a WSDL processor, acting on behalf of the client, encounters a required extension that it does not recognize or does not support, then it cannot safely continue to process the WSDL 2.0 document. In most practical cases, this is likely to mean that the processor will require manual intervention to deal with the extension. For example, a client developer might manually provide an implementation for the required extension to the WSDL processor.

7.1.2 Scoping of the wsdl:required Attribute

Editorial note: dbooth 2005-04-15
ToDo: Need to check the scoping rules to see if this is correct.

As a convenience mechanism, the wsdl:required attribute need not be specified on every extension element. If it is omitted from an extension element, its effective value is inherited from the smallest enclosing scope that explicitly sets its value. If there is no enclosing scope that explicitly sets its value, then its value defaults to false.

Because portions of a Web service description can be written in different physical documents by different people, one should be cautious about setting wsdl:required="false" when an outer scope, written by someone else, had set wsdl:required="true".

7.2 Features and Properties

After a few successful trials of the reservation service, GreatH decides that it is time to make the makeReservation operation secure, so that sensitive credit-card information is not being sent across the public network in a snoopable fashion. We will do this using the WSDL 2.0 Features and Properties mechanisms [WSDL 2.0 Core Language], which is modeled after the Features and Properties mechanism defined in SOAP 1.2 [SOAP 1.2 Part 1: Messaging Framework].

To facilitate presentation, this section will assume the existence of a hypothetical security feature named "http://features.example.com/2005/securityFeature", which defines, in the abstract, the idea of message confidentiality. This feature has an associated property, named "http://features.example.com/2005/securityFeature/securityLevel", which defines various safety levels (from 0 meaning clear text, all the way through 10, involving highly complex cryptographic algorithms with keys in the tens of thousands of bits). We also assume that a SOAP module, named "http://features.example.com/2005/modules/Security", has been defined, which implements the security feature described above.

GreatH has chosen an abstract security feature which is standard in the fictitious hotels community, and has integrated both a SOAP module and a new secure HTTP binding into its infrastructure – both of which implement the security feature (the SOAP module does this inside the SOAP envelope using headers, and the secure binding does it at the transport layer). Now they'd like to advertise and control the usage of these extensions using WSDL 2.0.

7.2.1 SOAP Modules

The first step GreatH takes is to require the usage of the SOAP module in their normal SOAP/HTTP endpoint, which looks like this:

Example 7-1. Requiring a SOAP Module in an Endpoint


. . .
<service name="reservationService" 
       interface="tns:reservationInterface">

  <endpoint name="reservationEndpoint" 
            binding="tns:reservationSOAPBinding"
            address ="http://greath.example.com/2004/reservation">
    <wsoap:module uri="http://features.example.com/2005/modules/Security"
              required="true"/>
  </endpoint>
        
</service>
. . .

This syntax indicates that a SOAP Module is required by this endpoint. This means that anyone using this endpoint must both understand the specification that the module URI references, and must use that specification when communicating with the endpoint in question, which typically means including appropriate SOAP headers on transmitted messages.

If the "required" attribute was not present, or if it was set to "false", then the <wsoap:module> syntax would indicate optional the availability of the referenced module, rather than a requirement to engage it, as explained in 7.1.1 Optional Versus Required Extensions.

7.2.2 Abstract Features

Since GreatH began the web service improvements, they have been talking to several travel agents. The possibility of making their simple hotel interface an industry standard amongst a consortium of hotels has come up, and as such they would like to enable specifying the requirement for the "makeReservation" operation to be secure at the interface level – in other words indicating that the operation must be secure, but without specifying exactly how that should concretely be achieved (to enable maximal reuse of the interface). The next example uses the WSDL 2.0 Feature element to indicate this.

Example 7-2. Declaring an Abstract Feature Requirement

. . .
<interface name="reservationInterface">
 <operation name="makeReservation">
  <feature uri="http://features.example.com/2005/securityFeature"
           required="true"/>
  . . . [The rest of the operation is unchanged] . . .
 </operation>
</interface>
. . .

This declaration indicates that understanding of, and compliance with, the specified security feature is required for all uses of the "makeReservation" operation. The security feature is abstract, which means that although it defines semantics and a level of detail about its general operation, it expects a concrete component (like a SOAP module or binding) to actually realize the functionality.

By definition, if you understand a SOAP module, you understand which (if any) abstract features it implements. Therefore, since the security module in this example is defined as an implementation of the abstract security feature, we know that the use of this module satisfies the requirement to implement the feature. Therefore users of the HTTP endpoint shown above (with the required SOAP module) will be able to make use of it. GreatH also defines a new endpoint:

Example 7-3. A SOAP Binding Over a Secure HTTP Protocol

. . .
<binding name="reservationSecureSOAPBinding"
    interface="tns:reservationInterface"
    type="http://www.w3.org/2005/05/wsdl/soap"
    wsoap:protocol="http://bindings.example.com/SOAPBindings/secureHTTP">
  . ..
</binding>
. . .
<service name="reservationService">
  . . .
  <endpoint name="secureReservationEndpoint"
            binding="tns:reservationSecureSOAPBinding"
            address="https://greath.example.com/2004/secureReservation"/>
</service>
. . .

The user will have a choice as to which of the endpoints, and therefore which binding, is to be used, but they both satisfy the abstract feature requirement specified in the interface.

Note that it is not necessary to declare the abstract feature in order to use/require the SOAP module, or in order to use/require the secure binding. Abstract feature declarations serve purely to indicate requirements which must be fulfilled by more concrete components such as modules or bindings. In other words, the abstract feature declaration allows components such as interfaces to be reused without caring exactly which SOAP modules or bindings satisfy the feature.

7.2.3 Properties

So far we've discussed how to indicate the availability or the "requiredness" of features and modules. Often it is not enough to indicate that a particular extension is available/required: you also need some way to control or parameterize aspects of its behavior. This is achieved by the use of WSDL 2.0 properties. Each feature, SOAP module, or SOAP binding may express a variety of properties in its specification. These properties are very much like variables in a programming language. If GreatH would like to indicate that the securityLevel property should be 5 for the "makeReservation" operation, it would look like this:

Example 7-4. Defining a Property

. . .
<interface name="reservationInterface">
 <operation name="makeReservation">
  <property
      uri="http://features.example.com/2005/securityFeature/securityLevel">
   <value>5</value>
  </property>
  . . . [rest of operation definition] . . .
 </operation>
</interface>
. . .

The property element specifies which property is to be set. By setting the value element, a toolkit processing this WSDL 2.0 document is informed that the securityLevel property must be set to 5. The particular meanings of any such values are up to the implementations of the modules/bindings that use them. The property element can be placed at many different levels in a WSDL 2.0 document (see "Property Composition Model", section 2.8.1.1 in WSDL 2.0 Part 1 [WSDL 2.0 Core Language]).

It is also possible to provide a constraint on the value space for a given property. This allows the author of the WSDL 2.0 document to indicate that several valid values for the property are possible for a given scope, limiting the value space already described in the specification that defined the property. Let's extend our example to make this clearer.

The security feature specification defines securityLevel as an integer with values between 1 and 10, each of which indicates, according to the spec, a progressively higher level of security. The GreatH service authors, having read the relevant specifications, have decided that any security level between 3 and 7 will be supported by their infrastructure. Levels less than 3 are deemed unsafe for GreatH's purposes, and levels greater than 7 require too much in the way of resources to make it worthwhile. We can express this in WSDL 2.0 as follows:

Example 7-5. Defining Property Constraints

. . .
<types>
 <schema>
  <simpleType name="securityLevelConstraint">
   <restriction base="xs:int">
    <min 3, max 7> <!-- check schema for syntax -->
   </restriction>
  </simpleType>
 </schema>
</types>
. . .
<property uri="http://features.example.com/2005/securityFeature/securityLevel">
  <constraint type="tns:securityLevelConstraint">
</property>
. . .

First we define, in the types section, an XML Schema restriction type over integers with minimum and maximum values, per our discussion above. Then instead of using the value element inside property, we use constraint and refer to the restriction type. This informs the implementation that the property must have the appropriate values. This information might be useful to a deployment user interface, for example, which might allow an administrator to set this value with a slider when deploying the service.

7.3 Import mechanism and authoring style

In some circumstances you may want to split up a Web service description into two or more documents. For example, if a description is getting long or is being developed by several authors, then it is convenient to divide it into several parts. Another very important case is when you expect parts of the description to be reused in several contexts. Clearly it is undesirable to cut and paste sections of one document into another, since that is error prone and leads to maintenance problems. More importantly, you may need to reuse components that belong to a wsdl:targetNamespace that is different than that of the document you are writing, in which case the rules of WSDL 2.0 prevent you from simply cutting and pasting them into your document.

To solve these problems, WSDL 2.0 provides two mechanisms for modularizing Web service description documents: import and include. This section discusses the import mechanism and describes some typical cases where it is be used.

The import mechanism lets you refer to the definitions of Web service components that belong to other namespaces. To illustrate this, consider the GreatH hotel reservation service. Suppose that the reservation service uses a standard credit card validation service that is provided by a financial services company. Furthermore, suppose that companies in the financial services industry decided that it would be useful to report errors in credit card validation using a common set of faults, and have defined these faults in the following Web service description:

Example 7-6. Standard Credit Card Validation Faults (credit-card-faults.wsdl)

<?xml version="1.0" encoding="utf-8" ?>
<description xmlns="http://www.w3.org/2005/05/wsdl"
        targetNamespace="http://finance.example.com/CreditCards/wsdl"
        xmlns:tns="http://finance.example.com/CreditCards/wsdl"
        xmlns:cc="http://finance.example.com/CreditCards/xsd">

  <documentation>
        This document describes standard faults for use 
      by Web services that process credit cards.
  </documentation>

  <types>
        <xs:import xmlns:xs="http://www.w3.org/2001/XMLSchema"
            namespace="http://finance.example.com/CreditCardFaults/xsd"
            schemaLocation="credit-card-faults.xsd" />
  </types>

  <interface name="creditCardFaults">

        <fault name="cancelledCreditCard" element="cc:CancelledCreditCard">
            <documentation>Thrown when the credit card has been cancelled.</documentation>
        </fault>
                
        <fault name="expiredCreditCard" element="cc:ExpiredCreditCard">
            <documentation>Thrown when the credit card has expired.</documentation>
        </fault>
                
        <fault name="invalidCreditCardNumber" element="cc:InvalidCreditCardNumber">
            <documentation>Thrown when the credit card number is invalid.
                This fault will occur if the wrong credit card type is specified.
          </documentation>
        </fault>
                
        <fault name="invalidExpirationDate" element="cc:InvalidExpirationDate">
            <documentation>Thrown when the expiration date is invalid.</documentation>
        </fault>

  </interface>

</description>

This example defines an interface, creditCardFaults, that contains four faults, cancelledCreditCard, expiredCreditCard, invalidCreditCardNumber, and invalidExpirationDate. These components belong to the namespace http://finance.example.com/CreditCards/wsdl.

Because these faults are defined in a different wsdl:targetNamespace than the one used by the GreatH Web service description, import must be used to make them available within the GreatH Web service description, as shown in the following example:

Example 7-7. Using the Standard Credit Card Validation Faults (use-credit-card-faults.wsdl)

<?xml version="1.0"?>
<description
        targetNamespace="http://greath.example.com/2004/wsdl/resSvc"
        xmlns:ghns="http://greath.example.com/2004/schemas/resSvc"
        xmlns:cc="http://finance.example.com/CreditCards/wsdl"
        xmlns="http://www.w3.org/2005/05/wsdl"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">

        <documentation>
                Description: The definition of the reservation Web service of
                GreatH hotel. Author: Joe Somebody Date: 05/17/2004
        </documentation>
        
        <import namespace="http://finance.example.com/CreditCards/wsdl" 
              location="credit-card-faults.wsdl"/>
        . . .
        <interface name="reservation" extends="cc:creditCardFaults">
                . . . 
                <operation name="makeReservation"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">

                        <input messageLabel="In" element="ghns:makeReservation" />

                        <output messageLabel="Out"
                                element="ghns:makeReservationResponse" />

                        <outfault ref="invalidDataFault" messageLabel="Out" />

                        <outfault ref="cc:cancelledCreditCard" messageLabel="Out" />
                        <outfault ref="cc:expiredCreditCard" messageLabel="Out" />
                        <outfault ref="cc:invalidCreditCardNumber" messageLabel="Out" />
                        <outfault ref="cc:invalidExpirationDate" messageLabel="Out" />
                </operation>
        </interface>
</description>

The hotel reservation service declares that it is using components from another namespace via the import> element. The import element has a required namespace attribute that specifies the other namespace, and an optional location attribute that gives the processor a hint where to find the description of the other namespace. The reservation interface extends the creditCardFault interface from the other namespace in order to make the faults available in the reservation interface. Finally, the makeReservation operation refers to the standard faults in its outfault elements.

Another typical situation for using imports is to define a standard interface that is to be implemented by many services. For example, suppose the hotel industry decided that it was useful to have a standard interface for making reservations. This interface would belong to some industry association namespace, e.g. http://hotels.example.com/reservations/wsdl. Each hotel that implemented the standard reservation service would define a service in its own namespace, e.g. http://greath.example.com/2004/wsdl/resSvc. The description of each service would import the http://hotels.example.com/reservations/wsdl namespace and refer to the standard reservation interface in it.

7.4 Multiple Interfaces for the Same Service

Suppose a Web service wishes to expose two different interfaces: a customer interface for its regular users, and a management interface for its operator. A wsdl:service specifies only one wsdl:interface, so to achieve the desired effect the service provider would somehow need to indicate a relationship between two services. How can a service provider indicate a relationship between services? Potential strategies include:

  • Declare both interfaces in the same wsdl:description element. Although WSDL 2.0 does not ascribe any particular significance to the fact that two wsdl:services are declared within the same wsdl:description, an application or toolkit could interpret this to mean that they are related in some way.

  • Declare both interfaces in the same wsdl:targetNamespace. Again, although WSDL 2.0 does not ascribe any particular significance to the fact that two wsdl:services are declared within the same wsdl:targetNamespace, an application or toolkit could interpret this to mean that they are related in some way.

  • Add an extension to WSDL 2.0 that links together all services that are related in this way. WSDL 2.0's open content model permits extension elements from other namespaces to appear in a WSDL 2.0 document.

  • Declare them in completely separate WSDL documents, but use the same endpoint address for both. I.e., declare a wsdl:interface and wsdl:service for the customer interface in one WSDL document, and a wsdl:interface and wsdl:service for the management interface in a different WSDL document, but use the same endpoint address for both. (By "different WSDL document" we mean that both documents are never included or imported into the same WSDL 2.0 descriptions component.) Although this approach may work in some circumstances, it means that the same endpoint address would be used for two different purposes, which is apt to cause confusion or ambiguity. Furthermore, it is contrary to the Web architectural principle that different URIs should be used to identify different Web resources. (See the Web Architecture [Web Architecture] section on URI collision.)

  • Use inheritance to combine the customer interface and management interface into a single, larger wsdl:interface. Of course, this reduces modularity and means that the management interface becomes exposed to the customers, which is not good.

Bear in mind that since the above strategies step outside of the WSDL 2.0 language specifies (and are therefore neither endorsed nor forbidden by the WSDL 2.0 specification) the WSDL 2.0 specification cannot define or standardize their semantics.

The desire to express relationships between services is also relevant to Web service versioning, discussed next.

7.5 Web Service Versioning

A WSDL 2.0 document describes a set of messages that a Web service may send and receive. In essence, it describes a language for interacting with that service. However it is possible for a Web service to exchange other messages beyond those described in a particular WSDL 2.0 document. Often this circumstance occurs following an evolution of the client and/or service, and thus an evolution of the interaction language.

How best to manage the evolution (versioning) of Web based systems is, at the time of writing, the subject of a wide ranging debate. However, there are three activities within the W3C that are directly relevant to versioning of Web services description:

While incomplete, these activities all agree in one important respect: that versioning is difficult, but you SHOULD anticipate and plan for change.

The draft finding on Versioning and Extensibility details two key approaches to versioning:

  • compatible evolution; and

  • big bang.

7.5.1 Compatible Evolution

In compatible evolution, designers are expected to limit changes to those that are either backward or forward compatible, or both:

Backward compatible

The receiver behaves correctly if it receives a message in an older version of the interaction language.

Forward compatible

The receiver behaves correctly if it receives a message in a newer version of the interaction language.

Since Web services and their clients both send and receive messages, these concepts can apply to both parties. However, since WSDL 2.0 is service-centric, we will focus on the case of service evolution.

There are three critical areas in which a service described in WSDL 2.0 my evolve:

  • The service now also supports additional binding. In compatible evolution, this should be a safe addition, given that adding a new binding should not impact any existing interactions using another transport.

  • An interface supports new operations. Again, in compatible evolution this is usually safe, given that adding an additional operation to an abstract interface should not impact any existing interactions.

  • The messages exchanged may include additional data. How the messages themselves may change within a description depends to a large extent upon the type system being used to describe the message contents. RelaxNG [RELAX NG] has good support for describing vocabularies that ignore unknown XML, as does OWL/RDF. XML Schema 1.0 has limited support for extending the description of a message via the xs:any and xs:anyAttribute constructs. XML Schema 1.1 has been chartered to provide "changes necessary to provide better support for versioning of schemas", and it is anticipated that this will include improved support for more "open content" and therefore better support for compatible evolution of messages.

7.5.2 Big Bang

The big bang approach to versioning is the simplest to currently represent in WSDL 2.0. In this approach, any change to a WSDL 2.0 document implies a change to the document's namespace, a change to the interface implies a new interface namespace and a change to the message contents is communicated using a new message namespace. This approach has particular benefits where an agent may quickly tell if a service has changed by simply comparing the namespace value.

7.5.3 Combined Approaches

It is feasible to combine the "compatible evolution" and "big bang" approaches in a variety of different ways. For example, the namespace could be changed when message descriptions are changed, but the namespace could stay the same when new operations are added.

While the big bang approach is currently the easiest to implement in WSDL 2.0, it can lead to a large number of cloned interfaces that become difficult to manage, thus making the compatible approach preferable to many for widely distributed systems. In the end, the choice of a versioning strategy for Web services described in WSDL 2.0 is left as an exercise to the reader.

7.6 MTOM Support

This section shows how theSOAP Message Transmission Optimization Mechanism (MTOM) [SOAP MTOM] may be engaged in the WSDL 2.0 SOAP binding extension.

We will modify the CheckAvailability operation of the GreatH Hotel Reservation Service (Example 2-1) to return not only the room rate, but images of the room and the floorplan. This will involve modifying the checkAvailabilityResponse data structure to include binary data representing these two images, indicated by the xs:base64Binary data type. Here is an example:

Example 7-8. XML Schema with Optimizable Elements

. . .
<xs:element name="checkAvailabilityResponse">

  <xs:sequence>

    <xs:element name="rate" type="xs:double"/>

    <xs:element name="photo"
        type="xmime:base64Binary"
        xmime:expectedContentType="image/jpeg image/png" />

    <xs:element name="floorplan"
        xmime:expectedContentType="image/svg">
      <xs:simpleContent>
        <xs:restriction base="xs:base64Binary">
          <xs:attribute ref="xmime:contentType"
                fixed="image/svg" />
        </xs:restriction>
      </xs:simpleContent>
    </xs:element>

  </xs:sequence>

</xs:element>
. . .

 

Note the use of the xmime:expectedContentType and xmime:contentType attributes to declare the expected media type of the encoded data and to allow the client to indicate the type at runtime, respectively. These attributes are defined in Describing Media Content of Binary Data in XML [ref].

A checkAvailabilityResponse message conforming to this schema might look like this:

Example 7-9. Non-optimized SOAP Message with Embedded Binary Data


<soap:Envelope
    xmlns:soap='http://www.w3.org/2003/05/soap-envelope' 
    xmlns:xmime='http://www.w3.org/2005/05/xmlmime'>

  <soap:Body>
    <g:checkAvailabilityResponse
        xmlns:g="http://greath.example.com/2004/schemas/resSvc">

      <g:rate>129.95</g:rate>
      <g:photo xmime:contentType='image/png'>/aWKKapGGyQ=</g:photo>
      <g:floorplan xmime:contentType="image/svg">Faa7vROi2VQ=</g:floorplan>

    </g:checkAvailabilityResponse>
  </soap:Body>

</soap:Envelope>

While this (non-optimized) message satisfies the schema definition, a service may choose to allow or require that the binary data be sent in an optimized format using the Message Transmission and Optimization Mechanism (MTOM). The use of this feature by the WSDL 2.0 SOAP binding extension is indicated as follows:

Example 7-10. Specifying MTOM in a WSDL 2.0 Binding


  . . .
<binding name="reservationSOAPBinding" 
    interface="tns:reservationInterface"
    type="http://www.w3.org/2005/05/wsdl/soap"
    wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP">

 <operation ref="tns:opCheckAvailability" 
      wsoap:mep="http://www.w3.org/2003/05/soap/mep/request-response">

   <input name="checkAvailability" />

   <output name="checkAvailabilityResponse">
     <feature
       uri="http://www.w3.org/2003/06/soap/features/http-optimization"
       required="true" />
   </output>

  </operation>
    . . .
</binding>
. . .

The HTTP Message Transmission Optimization (MTOM) feature is engaged using the feature element. Note that the attribute required=�?true�? on the feature declaration indicates that the message must be encoded using the HTTP Optimization feature. If the attribute were required=�?false�? (or this attribute were absent), it would indicate that the use of MTOM is optional for this service: the service accepts either MTOM-encoded messages, or the embedded base64Binary data directly in the Body, and the client is free to send either form of message.

The example above shows MTOM enabled for a specific message within an operation. Placing the feature declaration as a child of operation would require (or enable if required=�?false�?) MTOM support for all the messages in that operation. Placing the feature declaration as a child of binding would require (or enable if required=�?false�?) MTOM support for all the operations in that interface.

7.7 RPC Style

Section 5.4.1 Operation Attributes mentioned that the (optional) style attribute of an interface operation is used to indicate that the operation conforms to a particular pre-defined operation style, or set of constraints. Actually, if desired the style attribute can hold a list of URIs, indicating that the operation simultaneously conforms to multiple styles.

Operation styles are named using URIs, in order to be unambiguous while still permitted new styles to be defined without requiring updates to the WSDL 2.0 language. WSDL 2.0 Part 2 [WSDL 2.0 Adjuncts] defines three such operation styles; one of these is the RPC Style (RPC Style).

The RPC Style is designed to facilitate programming language bindings to WSDL 2.0 constructs. It allows a WSDL 2.0 interface operation to be easily mapped to a method or function signature, such as a method signature in Java(TM) or C#. RPC Style is restricted to operations that use the In-Out or In-Only MEPs (see 5.4.3 Understanding Message Exchange Patterns (MEPs)).

A WSDL 2.0 document makes use of the RPC Style in an interface operation by first defining the operation in conformance with all of the RPC Style rules, and then setting that operation's style attribute to include the URI that identifies the RPC Style, thus asserting that the operation does indeed conform to the RPC Style. These rules permit the input and output message schemas to map conveniently to inputs and outputs of a method signature. Roughly, input elements map to input parameters, output elements map to output parameters, and elements that appear both in the input and output message schemas map to input/output parameters. WSDL 2.0 Part 2 section "RPC Style" provides full details of the mapping rules and requirements.

The RPC Style also permits the full signature of the intended mapping to be indicated explicitly, using the wrpc:signature attribute defined in WSDL 2.0 Part 2 section "wrpc:signature Extension". This is an (optional) extension to the WSDL 2.0 language whose value designates how input and output message schema elements map to input and output parameters in the method signature.

The example below illustrates how RPC Style may be used to designate a signature. This example is a modified version of the GreatH reservation service. In particular, the interface and types sections have been modified to specify and conform to the RPC Style.

Example 7-11. Specifying RPC Style

. . .
<types>

  <xs:element name="checkAvailability">
    <xs:complexType>
      <xs:sequence>
          <xs:element  name="checkInDate" type="xs:date"/>
          <xs:element  name="checkOutDate" type="xs:date"/>
          <xs:element  name="roomType" type="xs:string"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:element name="checkAvailabilityResponse">
    <xs:complexType>
      <xs:sequence>
         <xs:element  name="roomType" type="xs:string"/>
         <xs:element  name="rateType" type="xs:string"/>
         <xs:element  name="rate" type="xs:double"/>
     </xs:sequence>
    </xs:complexType>
  </xs:element>
  . . .
</types>

<interface  name = "reservationInterface" >

  <operation name="checkAvailability"
        pattern="http://www.w3.org/2005/05/wsdl/in-out"
        style="http://www.w3.org/2005/05/wsdl/style/rpc"
        wrpc:signature=
          "checkInDate #in checkOutDate #in roomType #inout rateType #out rate #return">
    <input messageLabel="In"
          element="tns:checkAvailability" />
    <output messageLabel="Out"
          element="tns:checkAvailabilityResponse" />

  </operation>
. . .
</interface>
. . .

Note that the interface operation's name "checkAvailability", is the same as the localPart of the input element's QName, "tns:checkAvailability". This is one of the requirements of the RPC Style. The name of the operation is used as the name of the method in a language binding, subject to further mapping restrictions specific to the target programming language. In this case, the name of the method would be "checkAvailability".

The local children elements of the input element and output element designate the parameters and the return type for a method call. Note that the elements checkInDate, checkOutDate are input parameters, however the element roomType is an in-out parameter, as it appears both as a local element child of both input and output elements. This indicates that the reservation system may change the room type requested based on availability.

The reservation service also returns a rate type for the reservation, such as "rack rate". The return value for the method is designated as the "rate" element.

Based on the value of the wrpc:signature attribute, the method signature would be obtained following the order of the parameters. A sample mapping is provided below for the Java(TM) language. This example was created using JAX RPC 1.1 [JAX RPC 1.1] for mapping simple types to Java types and designated inout and output parameters by using Holder classes.

Example 7-12. Sample Java(TM) Signature for RPC Style

public interface reservationInterface extends Remote{

   double checkAvailability(java.util.calendar checkInDate,
              java.util.calendar checkOutDate,
              StringHolder roomType, 
              StringHolder rateType) throws RemoteException; 
    . . .
}

Programming languages may further specify how faults are mapped to langauage constructs and their scopes, such as Exceptions, but they are not specific to RPC style.

7.8 Enabling Easy Message Dispatch

Suppose a WSDL 2.0 document has two input-output operations and uses the same input message schema for both. When the service receives the input message, how will the service know which operation is supposed to be invoked? Although the data contained in a runtime message may be sufficient to distinguish between the operations, this can be a problem for WSDL 2.0 toolkits that are looking only at the message schema, rather than the actual messages. (For example, the toolkit may be operating at design time, without access to the runtime messages.) This is the problem of dispatch. How can a WSDL 2.0 document be written to ensure easy message dispatch? Strategies include:

  • Use unique top-level elements, i.e., ensure that the top-level elements declared in the message schemas are different for different operations. This is probably the most general solution, since it is guaranteed to provide a way to perform dispatch, without preventing toolkits from potentially using other dispatch techniques.

  • Include a required extension that enables a particular dispatching convention. This approach makes the dispatching convention explicit, although it may not be supported by every WSDL toolkit. However, as explained in 7.1.1 Optional Versus Required Extensions, toolkits that do not natively support the extension could seek manual input, thus permitting a client developer to supply an appropriate module that implements the necessary extension. This strategy has thus permits future WSDL toolkits to support and process the extension automatically, while also ensuring that the extension will be handled properly by toolkits that are not yet able to process it automatically.

To ensure that client and service implementations can easily determine the interface operation under which a received message was sent (even though not every client or service may need to make such a determination), it is considered good practice to follow one of the above strategies when authoring WSDL 2.0 documents.

7.9 Service and Endpoint References

Hyperlinking is one of the defining characteristics of the Web. The ability to navigate from one Web page to another is extremely useful. It is therefore natural to apply this capability to Web services. This section describes service references and endpoint references, which are the Web service analogs of document hyperlinks.

One may wonder, from a Web architectural point of view, why anything more than a URI would be needed to reference a Web service. Indeed, a service reference does make use of a URI to indicate the endpoint address of a service. However, it may also include additional metadata about that service, such as the WSDL 2.0 interface and binding that the service supports.

Service and endpoint references will be illustrated by expanding the GreatH example already discussed.

7.9.1 The Reservation Details Web Service

When designing a Web application it is natural to give each important concept a URI. In the GreatH hotel reservation system, the important concepts are reservations, so we begin our design by assigning a URI to each reservation. Since each reservation has a unique confirmation number, e.g OMX736, we create a URI for each reservation by appending the confirmation number to a base URI, e.g. http://greath.example.com/2004/reservation/OMX736. This URI will be the endpoint address for a Reservation Details Web service that can retrieve and update the state of a reservation. Example 7-13 shows the format of the reservation detail.

Example 7-13. Detail for Reservation OMX736

<?xml version="1.0" encoding="UTF-8"?>
<reservationDetails
        xmlns="http://greath.example.com/2004/schemas/reservationDetails">

        <confirmationNumber>OMX736</confirmationNumber>
        <checkInDate>2005-06-01</checkInDate>
        <checkOutDate>2005-06-03</checkOutDate>
        <roomType>single</roomType>
        <smoking>false</smoking>

</reservationDetails>

The Reservation Details Web service provides operations for retrieving and updating the detail for a reservation. Example 7-14 shows the description for this Web service. Note that there is no wsdl:service element in this description since the set of reservations is dynamic. Instead, the endpoints for the reservations will be returned by querying the Reservation List Web service.

Example 7-14. The Reservation Details Web Service Description: reservationDetails.wsdl

<?xml version="1.0" encoding="utf-8" ?>
<description xmlns="http://www.w3.org/2005/05/wsdl"
        targetNamespace="http://greath.example.com/2004/services/reservationDetails"
        xmlns:tns="http://greath.example.com/2004/services/reservationDetails"
        xmlns:wdetails="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:wsoap="http://www.w3.org/2005/05/wsdl/soap"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">

        <documentation>
                This document describes the GreatH Reservation Details Web
                services. Use these services to retrieve or update reservation
                details. Each reservation has its own service and endpoint. To
                obtain the serice reference for a reservation, make a request to
                the GreatH Reservation List Web service. See
                reservationList.wsdl for a description of the Reservation List
                Web service.
        </documentation>

        <types>
                <xs:import
                        namespace="http://greath.example.com/2004/schemas/reservationDetails"
                        schemaLocation="reservationDetails.xsd" />
        </types>

        <interface name="reservationDetailsInterface">

                <operation name="retrieve"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">
                        <input messageLabel="In" element="#none" />
                        <output messageLabel="Out"
                                element="wdetails:reservationDetails" />
                </operation>

                <operation name="update"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">
                        <input messageLabel="In"
                                element="wdetails:reservationDetails" />
                        <output messageLabel="Out"
                                element="wdetails:reservationDetails" />
                </operation>

        </interface>

        <binding name="reservationDetailsSOAPBinding"
                interface="tns:reservationDetailsInterface"
                type="http://www.w3.org/2005/05/wsdl/soap"
                wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP">

                <operation ref="tns:retrieve"
                        wsoap:mep="http://www.w3.org/2003/05/soap/mep/request-response" />

                <operation ref="tns:update"
                        wsoap:mep="http://www.w3.org/2003/05/soap/mep/request-response" />

        </binding>

</description>

Example 7-15 shows the XML schema elements that are used in this Web service.

Example 7-15. The Reservation Details Web Service XML Schema: reservationDetails.xsd

<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema"
        elementFormDefault="qualified"
        targetNamespace="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:tns="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:wdetails="http://greath.example.com/2004/services/reservationDetails"
        xmlns:wsdl="http://www.w3.org/2005/05/wsdl"
        xmlns:wsdli="http://www.w3.org/2005/05/wsdl-instance">

        <import namespace="http://www.w3.org/2005/05/wsdl" />

        <import namespace="http://www.w3.org/2005/05/wsdl-instance" />

        <element name="confirmationNumber" type="string" />

        <element name="checkInDate" type="date" />

        <element name="checkOutDate" type="date" />

        <element name="reservationDetails">
                <complexType>
                        <sequence>
                                <element ref="tns:confirmationNumber" />
                                <element ref="tns:checkInDate" />
                                <element ref="tns:checkOutDate" />
                                <element name="roomType" type="string" />
                                <element name="smoking" type="boolean" />
                        </sequence>
                </complexType>
        </element>

        <complexType name="ReservationDetailsSOAPEndpointType">
                <complexContent>
                        <restriction base="wsdl:EndpointType">
                                <attribute name="binding" type="QName" use="required"
                                        fixed="wdetails:reservationDetailsSOAPBinding" />
                        </restriction>
                </complexContent>
        </complexType>

        <element name="reservationDetailsSOAPEndpoint"
                type="tns:ReservationDetailsSOAPEndpointType">
                <annotation>
                        <documentation>
                                This element contains a reference to the Reservation
                                Details Web Service SOAP Endpoint for this reservation.
                        </documentation>
                </annotation>
        </element>

        <complexType name="ReservationDetailsServiceType">
                <complexContent>
                        <restriction base="wsdl:ServiceType">
                                <sequence>
                                        <sequence>
                                                <element ref='wsdl:documentation' minOccurs='0'
                                                        maxOccurs='0' />
                                        </sequence>
                                        <choice minOccurs='1' maxOccurs='unbounded'>
                                                <element ref='wsdl:endpoint' />
                                        </choice>
                                </sequence>
                                <attribute name="interface" type="QName" use="required"
                                        fixed="wdetails:reservationDetailsInterface" />
                                <attribute ref="wsdli:wsdlLocation" />
                        </restriction>
                </complexContent>
        </complexType>

        <element name="reservationDetailsService"
                type="tns:ReservationDetailsServiceType">
                <annotation>
                        <documentation>
                                This element contains a reference to the Reservation
                                Details Web Service for this reservation.
                        </documentation>
                </annotation>
        </element>

</schema>

This XML schema contains the usual definitions for the elements that appear in the messages of the Web service. For example, the reservationDetails element is used in the messages of the retrieve and update operations. In addition, the schema defines two restrictions of WSDL complex types. The ReservationDetailsEndpointType complex type restricts the wsdl:EndpointType complex type to have a binding attribute whose value is the Reservation Details binding, wdetails:reservationDetailsSOAPBinding. The reservationDetailsSOAPEndpoint element is thus a restriction of the wsdl:endpoint element that has the binding for the Reservation Details service. This element will be used in the Reservation List service.

The schema also defines the ReservationDetailsServiceType complex type to restrict the wsdl:ServiceType to have an interface attribute whose value is the Reservation Details service interace, wdetails:reservationDetailsInterface. The reservationDetailsService element is thus a restriction of the wsdl:service element that has the interface for the Reservation Details service. Note that the attributes of the ReservationDetailsServiceType complex type have also been restricted to allow only the additional wsdli:wsdlLocation attribute, which will be used in Example 7-19 to specify the location of the WSDL 2.0 document that contains the definition of the wdetails:reservationDetailsInterface interface.

In general, when you want to describe messages that contain endpoint references, you may use elements that are based on the wsdl:EndpointType complex type. If the bindings of the endpoints are fixed, you can define a restriction of the wsdl:EndpointType complex type that has a fixed value for the binding attribute. Similarly, when you want to describe messages that contain service references, you may use elements that are based on the wsdl:ServiceType complex type. If the interfaces of the services are fixed, you can define a restriction of the wsdl:ServiceType complex type that has a fixed value for the interface attribute. Note that the rules of XML Schema do not allow wsdl:ServiceType to be further restricted to have a fixed value for the binding attribute of its nested wsdl:endpoint elements.

7.9.2 The Reservation List Web Service

Since the set of reservations changes as reservations are made and cancelled, the Reservation Detail endpoints are not described in a fixed WSDL document. Instead they are returned as endpoint references in response to requests made on a Reservation List Web service. The endpoint for the Reservation List service will be http://greath.example.com/2004/reservationList.

Example 7-16 shows the format of the response from the Reservation List service.

Example 7-16. Response from the Reservation List Web Service

<?xml version="1.0" encoding="UTF-8"?>
<reservationList
        xmlns="http://greath.example.com/2004/schemas/reservationList"
        xmlns:details="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:wdetails="http://greath.example.com/2004/services/reservationDetails"
        xmlns:wsdl="http://www.w3.org/2005/05/wsdl"
        xmlns:wsdli="http://www.w3.org/2005/05/wsdl-instance"
        wsdli:wsdlLocation="http://greath.example.com/2004/services/reservationDetails reservationDetails.wsdl">

        <reservation>
                <details:confirmationNumber>HSG635</details:confirmationNumber>
                <details:checkInDate>2005-06-27</details:checkInDate>
                <details:checkOutDate>2005-06-28</details:checkOutDate>
                <details:reservationDetailsSOAPEndpoint
                        binding="wdetails:reservationDetailsSOAPBinding"
                        address="http://greath.example.com/2004/reservation/HSG635" />
        </reservation>

        <reservation>
                <details:confirmationNumber>OMX736</details:confirmationNumber>
                <details:checkInDate>2005-06-01</details:checkInDate>
                <details:checkOutDate>2005-06-03</details:checkOutDate>
                <details:reservationDetailsSOAPEndpoint
                        binding="wdetails:reservationDetailsSOAPBinding"
                        address="http://greath.example.com/2004/reservation/OMX736" />
        </reservation>

        <reservation>
                <details:confirmationNumber>WUH663</details:confirmationNumber>
                <details:checkInDate>2005-06-11</details:checkInDate>
                <details:checkOutDate>2005-06-15</details:checkOutDate>
                <details:reservationDetailsSOAPEndpoint
                        binding="wdetails:reservationDetailsSOAPBinding"
                        address="http://greath.example.com/2004/reservation/WUH663" />
        </reservation>

</reservationList>

Here, the <details:reservationDetailsSOAPEndpoint> elements contain endpoint references to the Reservation Details Web services for the reservations HSG635, OMX736, and WUH663. The endpoint references give the binding and endpoint address of each service. In this example, all endpoints have the same binding, i.e. wdetails:reservationDetailsSOAPBinding . This QName identifies the WSDL 2.0 Binding component that is defined in a WSDL 2.0 document. This example shows the use of the wsdli:wsdlLocation attribute to locate the WSDL 2.0 document. The address of each endpoint is the URI assigned to each reservation.

Example 7-17 shows the description of the Reservation List Web service. Note that it contains operations to retrieve the entire list and to query for a list of reservations by confirmation number, check-in date, and check-out date. In each case, the operation returns a list of reservations.

Example 7-17. The Reservation List Web Service Description: reservationList.wsdl

<?xml version="1.0" encoding="utf-8" ?>
<description xmlns="http://www.w3.org/2005/05/wsdl"
        targetNamespace="http://greath.example.com/2004/services/reservationList"
        xmlns:tns="http://greath.example.com/2004/services/reservationList"
        xmlns:details="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:list="http://greath.example.com/2004/schemas/reservationList"
        xmlns:wsoap="http://www.w3.org/2005/05/wsdl/soap"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">

        <documentation>
                This document describes the GreatH Reservation List Web
                services. Use this service to retrieve lists of reservations
                based on a variety of search criteria.
        </documentation>

        <types>
                <xs:import
                        namespace="http://greath.example.com/2004/schemas/reservationDetails"
                        schemaLocation="reservationDetails.xsd" />
                <xs:import
                        namespace="http://greath.example.com/2004/schemas/reservationList"
                        schemaLocation="reservationList.xsd" />
        </types>

        <interface name="reservationListInterface">

                <operation name="retrieve"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">
                        <input messageLabel="In" element="#none" />
                        <output messageLabel="Out" element="list:reservationList" />
                </operation>

                <operation name="retrieveByConfirmationNumber"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">
                        <input messageLabel="In"
                                element="details:confirmationNumber" />
                        <output messageLabel="Out" element="list:reservationList" />
                </operation>

                <operation name="retrieveByCheckInDate"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">
                        <input messageLabel="In" element="details:checkInDate" />
                        <output messageLabel="Out" element="list:reservationList" />
                </operation>

                <operation name="retrieveByCheckOutDate"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">
                        <input messageLabel="In" element="details:checkOutDate" />
                        <output messageLabel="Out" element="list:reservationList" />
                </operation>

        </interface>

        <binding name="reservationListSOAPBinding"
                interface="tns:reservationListInterface"
                type="http://www.w3.org/2005/05/wsdl/soap"
                wsoap:protocol="http://www.w3.org/2003/05/soap/bindings/HTTP">

                <operation ref="tns:retrieve"
                        wsoap:mep="http://www.w3.org/2003/05/soap/mep/request-response" />

                <operation ref="tns:retrieveByConfirmationNumber"
                        wsoap:mep="http://www.w3.org/2003/05/soap/mep/request-response" />

                <operation ref="tns:retrieveByCheckInDate"
                        wsoap:mep="http://www.w3.org/2003/05/soap/mep/request-response" />

                <operation ref="tns:retrieveByCheckOutDate"
                        wsoap:mep="http://www.w3.org/2003/05/soap/mep/request-response" />

        </binding>

        <service name="reservationListService"
                interface="tns:reservationListInterface">

                <endpoint name="reservationListEndpoint"
                        binding="tns:reservationListSOAPBinding"
                        address="http://greath.example.com/2004/reservationList" />

        </service>

</description>

                                                

Example 7-18 shows the schema for the messages used in the Reservation List Web service.

Example 7-18. The Reservation List Schema: reservationList.xsd

<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema"
        elementFormDefault="qualified"
        targetNamespace="http://greath.example.com/2004/schemas/reservationList"
        xmlns:tns="http://greath.example.com/2004/schemas/reservationList"
        xmlns:details="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:wsdli="http://www.w3.org/2005/05/wsdl-instance">

        <import namespace="http://www.w3.org/2005/05/wsdl-instance" />

        <import
                namespace="http://greath.example.com/2004/schemas/reservationDetails"
                schemaLocation="reservationDetails.xsd" />

        <element name="reservation">
                <annotation>
                        <documentation>
                                A reservation contains the confirmation number, check-in
                                and check-out dates, and a reference to a Reservation
                                Details Web service.
                        </documentation>
                </annotation>
                <complexType>
                        <sequence>
                                <element ref="details:confirmationNumber" />
                                <element ref="details:checkInDate" />
                                <element ref="details:checkOutDate" />
                                <element ref="details:reservationDetailsSOAPEndpoint" />
                        </sequence>
                </complexType>
        </element>

        <element name="reservationList">
                <annotation>
                        <documentation>
                                A reservation list contains a sequence of zero or more
                                reservations.
                        </documentation>
                </annotation>
                <complexType>
                        <sequence>
                                <element ref="tns:reservation" minOccurs="0"
                                        maxOccurs="unbounded">
                                </element>
                        </sequence>
                        <attribute ref="wsdli:wsdlLocation" />
                </complexType>
        </element>

</schema>

In the preceeding example, there was a single endpoint associated with each Reservation Detail Web service. Suppose GreatH hotel decided to provide a second, secure endpoint. In this case, service references would be used to collect together the endpoints for each reservation. The reservationDetails.xsd schema defines the reservationDetailsService element for this purpose. It restricts the wsdl:ServiceType complex type to have a fixed value of reservationDetailsInterface for the interface attribute.

Example 7-19 shows an example of a message that contains a service reference for reservation HGS635. Note that the service contains two endpoints, one of which provides secure access to the Reservation Details Web service. Note the use of the wsdli:wsdlLocation to provide the location for the WSDL 2.0 document that defines the wdetails:reservationDetailsInterface interface and the wdetails:reservationDetailsSOAPBinding binding.

Example 7-19. A Service Reference to the Reservation Details Web Service

<?xml version="1.0" encoding="UTF-8"?>
<details:reservationDetailsService interface="wdetails:reservationDetailsInterface"
        xmlns:details="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:wdetails="http://greath.example.com/2004/services/reservationDetails"
        xmlns:wsdl="http://www.w3.org/2005/05/wsdl"
        xmlns:wsdli="http://www.w3.org/2005/05/wsdl-instance"
        wsdli:wsdlLocation="http://greath.example.com/2004/services/reservationDetails reservationDetails.wsdl">

                <wsdl:endpoint
                        name="SOAP"
                        binding="wdetails:reservationDetailsSOAPBinding"
                        address="http://greath.example.com/2004/reservation/HSG635" />
                        
                <wsdl:endpoint
                        name="SECURE-SOAP"
                        binding="wdetails:reservationDetailsSOAPBinding"
                        address="https://greath.example.com/2004/reservation/HSG635" />
                        
</details:reservationDetailsService>

7.9.3 Reservation Details Web Service Using HTTP Transfer

This section presents a variation on the example in 7.9.1 The Reservation Details Web Service. It illustrates the use of HTTP transfer operations, GET and PUT, to retrieve and update GreatH hotel reservation details using the Representational State Transfer (REST) architectural style described by Roy Fielding [REST]. REST is a distillation of the architectural properties that Dr. Fielding identified as being vital to the Web's robustness and enormous scalability.

Since each reservation in our example will have a distinct URI, the Reservation Details Web service can be offered using HTTP GET and HTTP PUT. The binding would be modified as follows:

Example 7-20. Reservation Details Web Service Using HTTP Transfer

                                                        . . .
<binding name="reservationDetailsHTTPBinding"
         type="http://www.w3.org/2005/05/wsdl/http"
         interface="tns:reservationDetailsInterface" >

        <operation ref="tns:retrieve"
            whttp:method="GET" />

        <operation ref="tns:update"
            whttp:method="PUT" />

</binding>
. . .
                                                

As with the example in 7.9.1 The Reservation Details Web Service, service and endpoint elements are not provided because the Reservation List Web service provides the endpoints.

7.9.4 Reservation List Web Service Using HTTP GET

This section continues the REST-style example of 7.9.3 Reservation Details Web Service Using HTTP Transfer by modifying the example of 7.9.2 The Reservation List Web Service to use HTTP GET.

The SOAP version of the Reservation List Web service above offers four different search operations. These can also be expressed as various parameters in a URI used by HTTP GET:

Example 7-21. Reservation List Web Service Using HTTP GET

                                                        . . .
<binding name="reservationListHTTPBinding"
    type="http://www.w3.org/2005/05/wsdl/http"
    interface="tns:reservationListInterface"
    whttp:methodDefault="GET">

  <operation ref="tns:retrieve"
      whttp:location="" />

  <operation ref="tns:retrieveByConfirmationNumber"
      whttp:location="reservationList/ConfirmationNumber/{confirmationNumber/}" />

  <operation ref="tns:retrieveByCheckInDate"
      whttp:location="reservationList/CheckInDate/{checkInDate/}" />

  <operation ref="tns:retrieveByCheckOutDate"
      whttp:location="reservationList/CheckOutDate/{checkOutDate/}" />
</binding>
. . .
<service . . . >

  <endpoint name="reservationListEndpoint"
    binding="tns:reservationListHTTPBinding"
    address="http://greath.example.com/2004/reservationList" />
. . .
</service>
. . .
                                                

A retrieval by Confirmation Number URI would look like: http://greath.example.com/2004/reservationList/ConfirmationNumber/HSG635 .

Alternatively, a single query type may be provided. This query type is a sequence of optional items. Any items in the sequence are serialized into the URI query string. A query sequence for any of ConfirmationNumber, checkInDate, checkOutDate would look like this:

Example 7-22. Query Sequence Using a Single Query Type

                                                        <element name="reservationQuery">
  <annotation>
    <documentation>
      A reservation contains the confirmation number, check-in
      and check-out dates, and a reference to a Reservation
      Details Web service.
    </documentation>
  </annotation>
  <complexType>
    <sequence>
      <element ref="details:confirmationNumber" minOccurs="0"/>
      <element ref="details:checkInDate" minOccurs="0"/>/>
      <element ref="details:checkOutDate" minOccurs="0"/>/>
    </sequence>
    </sequence>
  </complexType>
</element>
                                                

The WSDL service that offers this type serialized as a parameter would look like this:

Example 7-23. WSDL for Using a Single Query Type

                                                        . . .
<interface name="reservationListInterfaceWithQuery">

  <operation name="retrieveByReservationQuery"
      pattern="http://www.w3.org/2005/05/wsdl/in-out">
    <input messageLabel="In"
        element="details:ReservationQuery" />
    <output messageLabel="Out"
        element="list:reservationList" />
  </operation>

</interface>

<binding name="reservationListQueryHTTPBinding"
    type="http://www.w3.org/2005/05/wsdl/http"
    interface="tns:reservationListInterfaceWithQuery"
    whttp:methodDefault="GET">

  <operation ref="tns:retrieveByReservationQuery"
      whttp:location="reservationList/{ReservationQuery}}" />

</binding>

. . .
  <endpoint name="reservationListEndpoint"
      binding="tns:reservationListHTTPBinding"
      address="http://greath.example.com/2004/reservationList" />
. . .
                                                

Various URIs would be: http://greath.example.com/2004/reservationList/ReservationQuery?confirmationNumber=HSG635 http://greath.example.com/2004/reservationList/ReservationQuery?checkInDate=06-06-05 .

It is important to observe that using the URI serialization can result in very flexible queries and few operations. The previous discrete SOAP operations are collapsed into one "parameterized" operation.

7.10 Importing Schemas

WSDL 2.0 documents may contain one or more XML schemas defined within the wsdl:types element. This section illustrates the correct way to refer to these schemas, both from within the same document and from other documents.

7.10.1 Schemas in Imported Documents

In this example, we consider some GreatH Hotel Web services that retrieve and update reservation details. The retrieval Web service is defined in the retrieveDetails.wsdl WSDL 2.0 document, along with a schema for the message format. The updating Web service is defined in the updateDetails.wsdl WSDL 2.0 document which imports the first document and refers to both WSDL and schema definitions contained in the imported document.

Example 7-24 shows the definition of the retrieval Web service in the http://greath.example.com/2004/services/retrieveDetails namespace. This WSDL 2.0 document also contains an inline schema that describes the reservation detail in the http://greath.example.com/2004/schemas/reservationDetails namespace. This schema is visible to the retrieveDetailsInterface interface definition which refers to it in the retrieve operation's output message.

Example 7-24. The Retrieve Reservation Details Web Service: retrieveDetails.wsdl

                                                        <?xml version="1.0" encoding="utf-8" ?>
<description xmlns="http://www.w3.org/2005/05/wsdl"
        targetNamespace="http://greath.example.com/2004/services/retrieveDetails"
        xmlns:tns="http://greath.example.com/2004/services/retrieveDetails"
        xmlns:wdetails="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">

        <documentation>
                This document describes the GreatH Retrieve Reservation Details
                Web service.
        </documentation>

        <types>
                <xs:schema xmlns="http://www.w3.org/2001/XMLSchema"
                        targetNamespace="http://greath.example.com/2004/schemas/reservationDetails">

                        <xs:element name="reservationDetails">
                                <xs:complexType>
                                        <xs:sequence>
                                                <xs:element name="confirmationNumber"
                                                        type="string" />
                                                <xs:element name="checkInDate" type="date" />
                                                <xs:element name="checkOutDate" type="date" />
                                                <xs:element name="roomType" type="string" />
                                                <xs:element name="smoking" type="boolean" />
                                        </xs:sequence>
                                </xs:complexType>
                        </xs:element>
                </xs:schema>
        </types>

        <interface name="retrieveDetailsInterface">

                <operation name="retrieve"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">
                        <input messageLabel="In" element="#none" />
                        <output messageLabel="Out"
                                element="wdetails:reservationDetails" />
                </operation>

        </interface>

</description>
                                                

Example 7-25 shows the definition of the updating Web service in the http://greath.example.com/2004/services/updateDetails namespace. The updateDetailsInterface interface extends the retrieveDetailsInterface interface. However, the retrieveDetailsInterface belongs to the http://greath.example.com/2004/services/retrieveDetails namespace, so updateDetails.wsdl must import retrieveDetails.wsdl to make that namespace visible.

The updateDetailsInterface interface also uses the reservationDetails element definition that is contained in the inline schema of the imported retrieveDetails.wsdl document. However, this schema is not automatically visible within the updateDetails.wsdl document. To make it visible, the updateDetails.wsdl document must import the namespace of the inline schema within the types element using the XML schema import element.

In this example, the schemaLocation attribute of the import element has been omitted. The schemaLocation attribute is a hint to the WSDL processor that tells it where to look for the imported schema namespace. However, the WSDL processor has already processed the retrieveDetails.wsdl document which contains the imported namespace in an inline schema so it should not need any hints. However, this behavior depends on the implementation of the processor and so cannot be relied on.

Although the WSDL 2.0 document may validly omit the schemaLocation attribute, it is a best practice to either provide a reliable value for it or move the inline schema into a separate document, say reservationDetails.xsd, and directly import it in the types element of both retrieveDetails.wsdl and updateDetails.wsdl. In general, schemas that are expected to be referenced from more than one WSDL 2.0 document should be defined in a separate schema document rather than be inlined.

Example 7-25. The Update Reservation Details Web Service: updateDetails.wsdl

<?xml version="1.0" encoding="utf-8" ?>
<description xmlns="http://www.w3.org/2005/05/wsdl"
        targetNamespace="http://greath.example.com/2004/services/updateDetails"
        xmlns:tns="http://greath.example.com/2004/services/updateetails"
        xmlns:retrieve="http://greath.example.com/2004/services/retrieveDetails"
        xmlns:details="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">

        <documentation>
                This document describes the GreatH Update Reservation Details
                Web service.
        </documentation>

        <import
                namespace="http://greath.example.com/2004/services/retrieveDetails"
                location="retrieveDetails.wsdl" />

        <types>
                <xs:import
                        namespace="http://greath.example.com/2004/schemas/reservationDetails" />
        </types>

        <interface name="updateDetailsInterface"
                extends="retrieve:retrieveDetailsInterface">

                <operation name="update"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">
                        <input messageLabel="In"
                                element="details:reservationDetails" />
                        <output messageLabel="Out"
                                element="details:reservationDetails" />
                </operation>

        </interface>

</description>

7.10.2 Multiple Inline Schemas in One Document

A WSDL 2.0 document may define multiple inline schemas in its types element. The two or more schemas may have the same target namespace provided that they do not define the same elements or types. It is an error to define the same element or type more than once, even if the definitions are identical.

Each namespace of an inline schema becomes visible to the Web service definitions. However, the namespaces are not automatically visible to the other inline schemas. Each inline schema must explictly import any other namespace it references. The schemaLocation attribute is not required in this case since the WSDL processor knows the location of each schema by virtue of having processed the enclosing WSDL document.

To illustrate this, consider Example 7-26 which contains two inline schemas. The http://greath.example.com/2004/schemas/reservationItems namespace contains some elements for items that appear in the reservation details. The http://greath.example.com/2004/schemas/reservationDetails namespace contains the reservationDetails element which refers to the item elements. The schema for the http://greath.example.com/2004/schemas/reservationDetails namespace contains an import element that imports the http://greath.example.com/2004/schemas/reservationItems namespace. No schemaLocation attribute is required for this import since the schema is defined inline in the importing document.

Example 7-26. Multiple Inline Schemas: retrieveItems.wsdl

<?xml version="1.0" encoding="utf-8" ?>
<description xmlns="http://www.w3.org/2005/05/wsdl"
        targetNamespace="http://greath.example.com/2004/services/retrieveDetails"
        xmlns:tns="http://greath.example.com/2004/services/retrieveDetails"
        xmlns:wdetails="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">

        <documentation>
                This document describes the GreatH Retrieve Reservation Details
                Web service.
        </documentation>

        <types>

                <xs:schema targetNamespace="http://greath.example.com/2004/schemas/reservationItems">

                        <xs:element name="confirmationNumber" type="string" />
                        <xs:element name="checkInDate" type="date" />
                        <xs:element name="checkOutDate" type="date" />
                        <xs:element name="roomType" type="string" />
                        <xs:element name="smoking" type="boolean" />

                </xs:schema>

                <xs:schema targetNamespace="http://greath.example.com/2004/schemas/reservationDetails"
                        xmlns:items="http://greath.example.com/2004/schemas/reservationItems">

                        <xs:import
                                namespace="http://greath.example.com/2004/schemas/reservationItems" />

                        <xs:element name="reservationDetails">
                                <xs:complexType>
                                        <xs:sequence>
                                                <xs:element ref="items:confirmationNumber" />
                                                <xs:element ref="items:checkInDate" />
                                                <xs:element ref="items:checkOutDate" />
                                                <xs:element ref="items:roomType" />
                                                <xs:element ref="items:smoking" />
                                        </xs:sequence>
                                </xs:complexType>
                        </xs:element>
                </xs:schema>

        </types>

        <interface name="retrieveDetailsInterface">

                <operation name="retrieve"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">
                        <input messageLabel="In" element="#none" />
                        <output messageLabel="Out"
                                element="wdetails:reservationDetails" />
                </operation>

        </interface>

</description>

7.10.3 The schemaLocation Attribute

In the preceding examples, schemas were defined inline in WSDL 2.0 documents. This section discusses the correct way to specify a schemaLocation attribute on a schema import element to provide a processor with a hint for locating these schemas.

Example 7-25 shows how one WSDL 2.0 document imports a schema defined in another, i.e. Example 7-24. Similarly, Example 7-26 shows how one schema in a WSDL 2.0 document imports another schema defined in the same document. In both of these examples, the schemaLocation attribute was omitted since the WSDL processor was assumed to know how to locate the imported schemas because they were part of the WSDL documents being processed. The schemaLocation attribute can be used to give the processor a URI reference that explicitly locates the schemas. A URI reference is a URI plus an optional fragment identifier that indicates part of the resource. For schemas, the fragment should identify the schema element. The simplest way to accomplish this is to use the id attribute, however XPointer can also be used.

7.10.3.1 Using the id Attribute to Identify Inline Schemas

Example 7-27 shows the use of the id attribute. Both of the inline schemas have id attributes. The id of the http://greath.example.com/2004/schemas/reservationItems schema is items and the id of the http://greath.example.com/2004/schemas/reservationDetails schema is details. The import element in the http://greath.example.com/2004/schemas/reservationDetails schema uses the id of the http://greath.example.com/2004/schemas/reservationItems schema in the schemaLocation attribute, i.e. #items.

Example 7-27. Using Ids in Inline Schemas: schemaIds.wsdl

<?xml version="1.0" encoding="utf-8" ?>
<description xmlns="http://www.w3.org/2005/05/wsdl"
        targetNamespace="http://greath.example.com/2004/services/retrieveDetails"
        xmlns:tns="http://greath.example.com/2004/services/retrieveDetails"
        xmlns:wdetails="http://greath.example.com/2004/schemas/reservationDetails"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">

        <documentation>
                This document describes the GreatH Retrieve Reservation Details
                Web service.
        </documentation>

        <types>

                <xs:schema id="items"
                        targetNamespace="http://greath.example.com/2004/schemas/reservationItems">

                        <xs:element name="confirmationNumber" type="string" />
                        <xs:element name="checkInDate" type="date" />
                        <xs:element name="checkOutDate" type="date" />
                        <xs:element name="roomType" type="string" />
                        <xs:element name="smoking" type="boolean" />

                </xs:schema>

                <xs:schema id="details"
                        targetNamespace="http://greath.example.com/2004/schemas/reservationDetails"
                        xmlns:items="http://greath.example.com/2004/schemas/reservationItems">

                        <xs:import
                                namespace="http://greath.example.com/2004/schemas/reservationItems"
                                schemaLocation="#items" />

                        <xs:element name="reservationDetails">
                                <xs:complexType>
                                        <xs:sequence>
                                                <xs:element ref="items:confirmationNumber" />
                                                <xs:element ref="items:checkInDate" />
                                                <xs:element ref="items:checkOutDate" />
                                                <xs:element ref="items:roomType" />
                                                <xs:element ref="items:smoking" />
                                        </xs:sequence>
                                </xs:complexType>
                        </xs:element>
                </xs:schema>

        </types>

        <interface name="retrieveDetailsInterface">

                <operation name="retrieve"
                        pattern="http://www.w3.org/2005/05/wsdl/in-out">
                        <input messageLabel="In" element="#none" />
                        <output messageLabel="Out"
                                element="wdetails:reservationDetails" />
                </operation>

        </interface>

</description>

7.11 Mapping to RDF and Semantic Web

Editorial note: KevinL 20050429
This section might be removed - pending on the availability of the RDF mapping note.

WSDL 2.0 is a language designed primarily with XML syntax. While XML is almost universally understood, it has several issues:

  • The ability to compose two XML documents into one depends on the languages of those documents. WSDL 2.0 does not permit Web service descriptions in different targetNamespaces to be merged into a single (physical) XML document.

  • The ability to extend XML languages with other XML languages depends on the languages again. WSDL 2.0 is extremely extensible, but the meaning of every single extension in WSDL must be defined explicitly. Putting a piece of XMI (XML format for UML) into a WSDL 2.0 document may have different meaning from putting it into an XHTML document. Therefore XML-based extensibility has very high cost if many languages are involved.

  • Similarly, extending another XML language with pieces of WSDL 2.0, while possible, has to be defined for all the possible destinations. Putting a WSDL 2.0 interface element into a UDDI registry may mean a different thing from putting that interface element into an XHTML document.

  • Finally, the meaning of a portion of a WSDL 2.0 document is not defined by the WSDL 2.0 specification. While an interface element could form a single XML document, it is not a WSDL 2.0 document, so its meaning is largely undefined.

Applications that require such levels of composability (or decomposability) are increasingly being based on RDF [RDF], a graph-based knowledge representation language, and Web Ontology Language (OWL) [OWL], which can be thought of as an advanced schema language for RDF. Effectively, a WSDL 2.0 document represented in RDF can be more easily extended with arbitrary RDF assertions and the WSDL 2.0 information can be more easily associated with arbitrary other knowledge.

7.11.1 RDF Representation of WSDL 2.0

WSDL 2.0: Mapping to RDF @@bibref@@ describes how WSDL 2.0 constructs can be expressed in RDF using classes of resources (described with an ontology expressed in OWL) and assertions over individual resources. As RDF represents knowledge using resources and relationships between them, we need to turn WSDL 2.0 concepts into this model. This is done as follows.

  1. First, all components in WSDL 2.0 (like Interfaces, Operations, Bindings, Services, Endpoints etc., including extensions) are turned into resources identified with the appropriate URIs created according to @@Appendix C@@.

  2. Further, things are represented as resources:

    1. Element declarations gathered from XML Schema (or similarly, other components from other type systems)

    2. Message content models

    3. Message exchange patterns (the URI identifying the MEP is the URI of the resource)

    4. Operation styles (similarly to MEPs, the URI of an operation style is the URI of the resource)

  3. All the resources above are given the appropriate types using rdf:type statements (an interface will belong to the class Interface and an operation within an interface will belong to the class InterfaceOperation, for example).

  4. All relationships in WSDL 2.0 (like an Operation belonging to an Interface and having a given operation style) are turned into RDF statements using appropriate properties, such as operation and operationStyle.

7.12 Notes on URIs

This section provides background that may be useful when authoring a WSDL 2.0 document or implementing the WSDL 2.0 specification.

7.12.1 XML Namespaces and Schema Locations

It is a common misperception to equate either the target namespace of an XML Schema or the value of the xmlns attribute in XML instances with the location of the corresponding schema. Even though namespaces are URIs, and URIs may be locations, and it may be possible to retrieve a schema from such a location, this does not mean that the retrieved schema is the only schema that is associated with that namespace. There can be multiple schemas associated with a particular namespace, and it is up to a processor of XML to determine which one to use in a particular processing context. The WSDL specification provides the processing context here via the import mechanism, which is based on XML Schema's term for the similar concept.

7.12.2 Relative URIs

Throughout this document there are fully qualified URIs used in WSDL 2.0 and XSD examples. In some cases, the use of a fully qualified URI is simply to illustrate the referencing concepts. however, the use of relative URIs is allowed and warranted in many cases. For information on processing relative URIs, see RFC2396.

7.12.3 Generating Temporary URIs

In general, when a WSDL 2.0 document is published for use by others, it should contain URIs that are globally unique. This is usually done by allocating them under a domain name that is controlled by the issuer. For example, the W3C allocates namespace URIs under its base domain name, w3.org.

However, it is sometimes desirable to make up a temporary URI for an entity, for use during development, but not make the URI globally unique for all time and have it "mean" that version of the entity (schema, WSDL 2.0 document, etc.). Reserved Top Level DNS Names [IETF RFC 2606] specifies some URI base names that are reserved for use for this type of behavior. For example, the base URI "http://example.org/" can be used to construct a temporary URI without any unique association to an entity. This means that two people or programs could choose to simultaneously use the temporary URI " http://example.org/userSchema" for two completely different schemas. As long as the scope of use of these URIs does not intersect, then they would be unique enough. However, it is not recommended that " http://example.org/" be used as a base for stable, fixed entities.

8. References

@@ To do: Enable the reference to the RDF mapping when it's done. @@

8.1 Normative References

[IETF RFC 2119]
Key words for use in RFCs to Indicate Requirement Levels, S. Bradner, Author. Internet Engineering Task Force, June 1999. Available at http://www.ietf.org/rfc/rfc2119.txt.
[IETF RFC 2396]
Uniform Resource Identifiers (URI): Generic Syntax, T. Berners-Lee, R. Fielding, L. Masinter, Authors. Internet Engineering Task Force, August 1998. Available at http://www.ietf.org/rfc/rfc2396.txt.
[XML 1.0]
Extensible Markup Language (XML) 1.0 (Second Edition), T. Bray, J. Paoli, C. M. Sperberg-McQueen, and E. Maler, Editors. World Wide Web Consortium, 10 February 1998, revised 6 October 2000. This version of the XML 1.0 Recommendation is http://www.w3.org/TR/2000/REC-xml-20001006. The latest version of XML 1.0 is available at http://www.w3.org/TR/REC-xml.
[XML Information Set]
XML Information Set, J. Cowan and R. Tobin, Editors. World Wide Web Consortium, 24 October 2001. This version of the XML Information Set Recommendation is http://www.w3.org/TR/2001/REC-xml-infoset-20011024. The latest version of XML Information Set is available at http://www.w3.org/TR/xml-infoset.
[XML Namespaces]
Namespaces in XML, T. Bray, D. Hollander, and A. Layman, Editors. World Wide Web Consortium, 14 January 1999. This version of the XML Information Set Recommendation is http://www.w3.org/TR/1999/REC-xml-names-19990114. The latest version of Namespaces in XML is available at http://www.w3.org/TR/REC-xml-names.
[XML Schema: Structures]
XML Schema Part 1: Structures, H. Thompson, D. Beech, M. Maloney, and N. Mendelsohn, Editors. World Wide Web Consortium, 2 May 2001. This version of the XML Schema Part 1 Recommendation is http://www.w3.org/TR/2001/REC-xmlschema-1-20010502. The latest version of XML Schema Part 1 is available at http://www.w3.org/TR/xmlschema-1.
[XML Schema: Datatypes]
XML Schema Part 2: Datatypes, P. Byron and A. Malhotra, Editors. World Wide Web Consortium, 2 May 2001. This version of the XML Schema Part 2 Recommendation is http://www.w3.org/TR/2001/REC-xmlschema-2-20010502. The latest version of XML Schema Part 2 is available at http://www.w3.org/TR/xmlschema-2.
[RFC 3023]
IETF "RFC 3023: XML Media Types", M. Murata, S. St. Laurent, D. Kohn, July 1998. (See http://www.ietf.org/rfc/rfc3023.txt.)
[WSDL MediaType]
IETF Internet Draft "The 'application/wsdl+xml' media type", @@@. (Work to be done once we have consensus on the media type).
[WSDL 2.0 Core Language]
Web Services Description Language (WSDL) Version 2.0 Part 1: Core Language, R. Chinnici, M. Gudgin, J-J. Moreau, A. Ryman, J. Schlimmer, S. Weerawarana, Editors. World Wide Web Consortium, 3 August 2004. This version of the "Web Services Description Language (WSDL) Version 2.0 Part 1: Core Language" Specification is available at http://www.w3.org/TR/2005/WD-wsdl20-20050510. The latest version of "Web Services Description Language (WSDL) Version 2.0 Part 1: Core Language" is available at http://www.w3.org/TR/wsdl20.
[WSDL 2.0 Adjuncts]
Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts , M. Gudgin, H. Haas, P. Le Hégaret, A. Lewis, J-J. Moreau, D. Orchard, J. Schlimmer, S. Weerawarana, Editors. World Wide Web Consortium, 3 August 2004. This version of the "Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts" Specification is available at http://www.w3.org/TR/2005/WD-wsdl20-adjuncts-20050510. The latest version of "Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts" is available at http://www.w3.org/TR/wsdl20-adjuncts.
[Web Architecture]
Architecture of the World Wide Web, Volume One, Ian Jacobs, Norman Walsh, Editors. W3C Technical Architecture Group, 15 December, 2004. Available at http://www.w3.org/TR/2004/REC-webarch-20041215/ .
[WS Architecture]
Web Services Architecture, David Booth, Hugo Haas, Francis McCabe, Eric Newcomer, Michael Champion, Chris Ferris, David Orchard, Editors. W3C Web Services Architecture Working Group, 11 February 2004. Available at http://www.w3.org/TR/2004/NOTE-ws-arch-20040211/ .
[WS Glossary]
Web Services Glossary, Hugo Haas, Allen Brown, Editors. W3C Web Services Architecture Working Group, 11 February 2004. Available at http://www.w3.org/TR/2004/NOTE-ws-gloss-20040211/ .

8.2 Informative References

[IETF RFC 2045]
Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies, N. Freed, N. Borenstein, Authors. Internet Engineering Task Force, November 1996. Available at http://www.ietf.org/rfc/rfc2045.txt.
[IETF RFC 2606]
Reserved Top Level DNS Names, D. Eastlake, A. Panitz, Authors. Network Working Group, Internet Engineering Task Force, June 1999. Available at http://www.ietf.org/rfc/rfc2606.txt.
[IETF RFC 2616]
Hypertext Transfer Protocol -- HTTP/1.1, R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, T. Berners-Lee, Authors. Internet Engineering Task Force, June 1999. Available at http://www.ietf.org/rfc/rfc2616.txt.
[IETF RFC 2818]
HTTP Over TLS, E. Rescorla, Author. Internet Engineering Task Force, May 2000. Available at http://www.ietf.org/rfc/rfc2818.txt.
[SOAP 1.1]
Simple Object Access Protocol (SOAP) 1.1, D. Box, D. Ehnebuske, G. Kakivaya, A. Layman, N. Mendelsohn, H. Frystyk Nielsen, S. Thatte, D. Winer, Editors. World Wide Web Consortium, 8 May 2000. This version of the Simple Object Access Protocol 1.1 Note is http://www.w3.org/TR/2000/NOTE-SOAP-20000508.
[SOAP 1.2 Part 1: Messaging Framework]
SOAP Version 1.2 Part 1: Messaging Framework, M. Gudgin, M. Hadley, N. Mendelsohn, J-J. Moreau, H. Frystyk Nielsen, Editors. World Wide Web Consortium, 24 June 2003. This version of the "SOAP Version 1.2 Part 1: Messaging Framework" Recommendation is http://www.w3.org/TR/2003/REC-soap12-part1-20030624/. The latest version of "SOAP Version 1.2 Part 1: Messaging Framework" is available at http://www.w3.org/TR/soap12-part1/.
[SOAP MTOM]
SOAP Message Transmission Optimization Mechanism , M. Gudgin, N. Mendelsohn, M. Nottingham, H. Ruellan, Editors. World Wide Web Consortium, 25 January, 2005. This version of SOAP Message Transmission Optimization Mechanism is available at http://www.w3.org/TR/2005/REC-soap12-mtom-20050125/.
[XML Linking]
XML Linking Language (XLink) Version 1.0, S. DeRose, E. Maler, D. Orchard, Editors. World Wide Web Consortium, 27 June 2001. This version of the XML Linking Language 1.0 Recommendation is http://www.w3.org/TR/2001/REC-xlink-20010627. The latest version of XML Linking Language 1.0 is available at http://www.w3.org/TR/xlink.
[WSDL 1.1]
Web Services Description Language (WSDL) 1.1, E. Christensen, F. Curbera, G. Meredith, and S. Weerawarana, Authors. World Wide Web Consortium, 15 March 2002. This version of the Web Services Description Language 1.1 Note is http://www.w3.org/TR/2001/NOTE-wsdl-20010315. The latest version of Web Services Description Language 1.1 is available at http://www.w3.org/TR/wsdl.
[WSD Requirements]
Web Services Description Requirements, J. Schlimmer, Editor. World Wide Web Consortium, 28 October 2002. This version of the Web Services Description Requirements document is http://www.w3.org/TR/2002/WD-ws-desc-reqs-20021028. The latest version of Web Services Description Requirements is available at http://www.w3.org/TR/ws-desc-reqs.
[XPointer Framework]
XPointer Framework,Paul Grosso, Eve Maler, Jonathan Marsh, Norman Walsh, Editors. World Wide Web Consortium, 22 November 2002. This version of the XPointer Framework Proposed Recommendation is http://www.w3.org/TR/2003/REC-xptr-framework-20030325/ The latest version of XPointer Framework is available at http://www.w3.org/TR/xptr-framework/.
[W3C TAG Finding: Use of HTTP GET]
URIs, Addressability, and the use of HTTP GET and POST, Ian Jacobs, Editor. World Wide Web Consortium, 21 March 2004. This version of TAG finding is available at http://www.w3.org/2001/tag/doc/whenToUseGet.html
[W3C TAG Finding: Versioning]
Versioning XML Languages David Orchard, Norman Walsh. Proposed TAG Finding 16 November 2003. Available at http://www.w3.org/2001/tag/doc/versioning.html
[WebArch: Extensible Languages]
Web Architecture: Extensible Languages , Tim Berners-Lee, Dan Connolly, Authors. W3C Note 10 Feb 1998. Available at http://www.w3.org/TR/NOTE-webarch-extlang
[XML Schema: Versioning Use-Cases]
XML Schema Versioning Use Cases , Hoylen Sue. W3C XML Schema Working Group Draft, 15 April 2005. Available at http://www.w3.org/XML/2005/xsd-versioning-use-cases/
[SW VocabManagementNote]
Vocabulary Management , Thomas Baker, et al. Semantic Web Best Practices and Deployment Working Group Note, 8 Feb 2005. Available at http://esw.w3.org/topic/VocabManagementNote
[RELAX NG]
RELAX NG Specification, James Clark, MURATA Makoto, Editors. OASIS Committee Specification, 3 December 2001. Available at http://www.oasis-open.org/committees/relax-ng/spec-20011203.html
[JAX RPC 1.1]
Java(TM) API for XML-based Remote Procedure Call (JAX-RPC) Specification, version 1.1, Roberto Chinnici,et al. 14 October, 2003. Available at http://java.sun.com/xml/downloads/jaxrpc.html
[REST]
Representational State Transfer (REST), Roy Thomas Fielding, Author. 2000. Available at http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm
[RDF]
Resource Description Framework (RDF): Concepts and Abstract Syntax, Graham Klyne, Jeremy J. Carroll, Editors. W3C Recommendation, 10 February 2004. Available at http://www.w3.org/TR/rdf-concepts/
[OWL]
OWL Web Ontology Language Reference, Mike Dean,Guus Schreiber, Editors. W3C Recommendation 10 February 2004 . Available at http://www.w3.org/TR/owl-ref/

A. Acknowledgements (Non-Normative)

This document is the work of the W3C Web Service Description Working Group.

Members of the Working Group are (at the time of writing, and by alphabetical order): Rebecca Bergersen (IONA Technologies), Allen Brookes (Rogue Wave Softwave), Dave Chappell (Sonic Software), Helen Chen (Agfa-Gevaert N. V.), Roberto Chinnici (Sun Microsystems), Kendall Clark (University of Maryland), Ugo Corda (SeeBeyond), Glen Daniels (Sonic Software), Paul Downey (British Telecommunications), Youenn Fablet (Canon), Martin Gudgin (Microsoft Corporation), Hugo Haas (W3C), Tom Jordahl (Macromedia), Anish Karmarkar (Oracle Corporation), Jacek Kopecky (DERI Innsbruck at the Leopold-Franzens-Universität Innsbruck, Austria), Amelia Lewis (TIBCO Software, Inc.), Michael Liddy (Education.au Ltd.), Kevin Canyang Liu (SAP AG), Jonathan Marsh (Microsoft Corporation), Josephine Micallef (SAIC - Telcordia Technologies), Jeff Mischkinsky (Oracle Corporation), Dale Moberg (Cyclone Commerce), Jean-Jacques Moreau (Canon), Mark Nottingham (BEA Systems, Inc.), David Orchard (BEA Systems, Inc.), Bijan Parsia (University of Maryland), Tony Rogers (Computer Associates), Arthur Ryman (IBM), Adi Sakala (IONA Technologies), Igor Sedukhin (Computer Associates), Asir Vedamuthu (webMethods, Inc.), Sanjiva Weerawarana (Independent), Ümit Yalçınalp (SAP AG).

Previous members were: Lily Liu (webMethods, Inc.), Don Wright (Lexmark), Joyce Yang (Oracle Corporation), Daniel Schutzer (Citigroup), Dave Solo (Citigroup), Stefano Pogliani (Sun Microsystems), William Stumbo (Xerox), Stephen White (SeeBeyond), Barbara Zengler (DaimlerChrysler Research and Technology), Tim Finin (University of Maryland), Laurent De Teneuille (L'Echangeur), Johan Pauhlsson (L'Echangeur), Mark Jones (AT&T), Steve Lind (AT&T), Sandra Swearingen (U.S. Department of Defense, U.S. Air Force), Philippe Le Hégaret (W3C), Jim Hendler (University of Maryland), Dietmar Gaertner (Software AG), Michael Champion (Software AG), Don Mullen (TIBCO Software, Inc.), Steve Graham (Global Grid Forum), Steve Tuecke (Global Grid Forum), Michael Mahan (Nokia), Bryan Thompson (Hicks & Associates), Ingo Melzer (DaimlerChrysler Research and Technology), Sandeep Kumar (Cisco Systems), Alan Davies (SeeBeyond), Jacek Kopecky (Systinet), Mike Ballantyne (Electronic Data Systems), Mike Davoren (W. W. Grainger), Dan Kulp (IONA Technologies), Mike McHugh (W. W. Grainger), Michael Mealling (Verisign), Waqar Sadiq (Electronic Data Systems), Yaron Goland (BEA Systems, Inc.), Ümit Yalçınalp (Oracle Corporation), Peter Madziak (Agfa-Gevaert N. V.), Jeffrey Schlimmer (Microsoft Corporation), Hao He (The Thomson Corporation), Erik Ackerman (Lexmark), Jerry Thrasher (Lexmark), Prasad Yendluri (webMethods, Inc.), William Vambenepe (Hewlett-Packard Company), David Booth (W3C), Sanjiva Weerawarana (IBM).

The people who have contributed to discussions on www-ws-desc@w3.org are also gratefully acknowledged.