Semantic Annotations for WSDL and XML Schema — Usage Guide

1. Introduction

As the set of available Web Services expands, it becomes increasingly important to have automated tools to help identify services that match a requester's requirements. Finding suitable Web services automatically depends on the facilities available for service providers to describe the capabilities of their services and for service requesters to describe their requirements in an unambiguous and ideally, machine-interpretable form. Adding semantics to represent the requirements and capabilities of Web services is essential for achieving this unambiguity and machine-interpretability.

Semantics play an important role in all aspects of the lifecycle of Web services. During development, a service provider can explicate the intended semantics by annotating the appropriate parts of the Web service with concepts from a richer semantic model. Since semantic models provide agreement on the terms and intended use of terms, and may provide formal and informal definitions of the entities, there will be less ambiguity in the intended semantics of the provider. During discovery, a service requestor can describe the service requirements using terms from the semantic model. Reasoning techniques can be used to find service descriptions that match the request. During composition, these annotations can be used to aggregate the functionality of multiple services to create useful service compositions. Also, semantics based schema mappings can facilitate data transformations from which mediation code can be generated to enable Web services invocation. Therefore, once represented, semantics can be leveraged by tools to automate service discovery, mediation, composition and monitoring.

The World-Wide Web Consortium (W3C) standard Web Services Description Language (WSDL) specifies a standard way to describe the interfaces of a Web Service at a syntactic level and how to invoke it. However, WSDL does not explicitly provide mechanisms to specify the semantics of a Web service. Semantic Annotations for WSDL (SAWSDL) is an effort to define mechanisms by which semantic annotations can be added to WSDL components. This usage guide is an accompanying document to SAWSDL specification. It presents examples to illustrate how to associate semantic annotations with a Web service that could be used for classifying, discovering, matching, composing, and invoking Web services.

The sections in this document are organized to show how to associate semantic annotations with a WSDL document for use in service classification, discovery, matching, composition and invocation in that order.

1.1 Namespaces

The XML namespace names URIs used by this specification are as follows:

Prefix	Namespace name
xs	http://www.w3.org/2001/XMLSchema#
xsd	http://www.w3.org/2001/XMLSchema
sawsdl	http://www.w3.org/2002/ws/sawsdl/spec/sawsdl#
wsdl	http://www.w3.org/2006/01/wsdl
rdf	http://www.w3.org/1999/02/22-rdf-syntax-ns
rdfs	http://www.w3.org/2000/01/rdf-schema
owl	http://www.w3.org/2002/07/owl

1.2 Running Examples

Throughout this document, we use two Web services and several variations on these Web services to illustrate how semantic annoations on a WSDL can be used to do Web service interface matching and composition. One of these two Web services is presented as a request of a desirable Web service while the other is used as an advertisement or a service being offered by a service provider. Some readers may be new to the concept of representing the requirements of a client as a Web service - WSDL. While there may be different ways of representing the requirements of a client, in this document, for illustrative purposes we adopted the notion of a request WSDL where the requirements of a client are modeled as a Web service - WSDL. The inputs and outputs of this request WSDL codify the available inputs that a client can provide and the expected outputs from a service respectively. We then use the concepts of annotating a request similar to the way that one can annotate a service provider's WSDL and illustrate how a request WSDL interface can be matched, composed and transformed to invoke a service provider's advertised service.

We present these two Web services here so as to allow the reader to get familiarized with the examples used in the rest of the document. These are 'vanilla' WSDL files with no semantic annotations. In the following sections, these WSDLs are shown with suitable semantic annotations that suit the specific illustration. First a WSDL representation of a request WSDL is given followed by a service provider's advertisement WSDL.

<wsdl:description
  targetNamespace="http://org1.example.com/wsdl/CheckAvailabilityRequestService/"
  xmlns="http://org1.example.com/wsdl/CheckAvailabilityRequestService/"
  xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <wsdl:types>
   <xsd:schema targetNamespace=http://org1.example.com/wsdl/CheckAvailabilityRequestService">
    <xsd:element name="CheckAvailabilityRequestServiceRequest">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="itemCode" type="xsd:string"/>
          <xsd:element name="date" type="xsd:string"/>
          <xsd:element name="qty" type="xsd:float"/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    <xsd:element name="CheckAvailabilityRequestServiceResponse" type="itemConfirmation"/>
    <xsd:simpleType name="itemConfirmation">  
      <xsd:restriction base="xsd:boolean"/>
    </xsd:simpleType>
    </xsd:schema>
  </wsdl:types>

 <wsdl:interface name="CheckAvailabilityRequestService">
   <wsdl:operation name="CheckAvailabilityRequestOperation" pattern="http://www.w3.org/2006/01/wsdl/in-out">
   <wsdl:input element="CheckAvailabilityRequestServiceRequest"/>
   <wsdl:output element="CheckAvailabilityRequestServiceResponse"/>
    </wsdl:operation>
  </wsdl:interface>
 </wsdl:description>

Listing 1.2-1: WSDL excerpt for CheckAvailabilityRequest service. This example is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/CheckAvailabilityRequestService.wsdl.

<wsdl:description
  targetNamespace="http://org2.example.com/wsdl/CheckInventoryService/"
  xmlns="http://org2.example.com/wsdl/CheckInventoryService/"
  xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <wsdl:types>
    <xsd:schema targetNamespace="http://org2.example.com/wsdl/CheckInventoryService">
     <xsd:element name="CheckInventoryServiceRequest">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="SKU" type="xsd:string"/>
          <xsd:element name="deliveryDate" type="xsd:string"/>
          <xsd:element name="numBundles" type="xsd:float"/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    <xsd:element name="CheckInventoryServiceResponse">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="conf" type="xsd:boolean"/>
          <xsd:element name="numBundles_available" type="xsd:string"/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    </xsd:schema>
  </wsdl:types>

  <wsdl:interface name="CheckInventoryService">
    <wsdl:operation name="checkInventoryService" pattern="http://www.w3.org/2006/01/wsdl/in-out">
      <wsdl:input element="CheckInventoryServiceRequest"/>
      <wsdl:output element="CheckInventoryServiceResponse"/>
    </wsdl:operation>
  </wsdl:interface>
</wsdl:description>

Listing 1.2-2: WSDL excerpt for CheckInventoryService. This example is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/CheckInventoryService.wsdl.

2. Defining Annotations to Publish a Web Service

A Web service can be semantically annotated to carry categorization information that could be used to publish it for instance in a service registry. SAWSDL extension mechanism modelReference can be used to add this categorization information to Web services. This categorization information could be used when automatically publishing services in registries such as UDDI [UDDI]. Below, we illustrate a couple of ways in which categorization information can be associated with a Web service.

2.1 Adding Categorization Information When a Taxonomy Already Exists

If a categorization semantic model already exists (for example a taxonomy), then a modelReference element could be defined either on an interface or on an operation of a Web service to point to a particular categorization in the taxonomy. For example, if a purchase order taxonomy was created as shown in Listing 2.1-1 below (shown in RDF Turtle [Turtle] format for readability), then the interface of an item availability check Web service (introduced in Listing 1.2-1) could be annotated with taxonomy information as shown in Listing 2.1-2.

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix : <http://www.w3.org/2002/ws/sawsdl/spec/examples/taxonomy/POServiceClassification#> .

    <http://www.w3.org/2002/ws/sawsdl/spec/examples/taxonomy/POServiceClassification#> rdf:type owl:Ontology .
    :PurchaseOrderServices rdf:type owl:Class .
    :OrderModification rdf:type owl:Class;
       rdfs:subClassOf :PurchaseOrderServices .
    :ItemAvailabilityCheck rdf:type owl:Class;
       rdfs:subClassOf :PurchaseOrderServices .
    :OrderPlacement rdf:type owl:Class;
       rdfs:subClassOf :PurchaseOrderServices .
    :ProductInfoInquiry rdf:type owl:Class;
       rdfs:subClassOf :PurchaseOrderServices .
    :OrderTracking rdf:type owl:Class;
       rdfs:subClassOf :PurchaseOrderServices .

Listing 2.1-1: A taxonomy to organize Web services related to checking, placing, and tracking purchase orders. This taxonomy is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/taxonomy/POServiceClassification.

 ...
<wsdl:interface name="CheckItemAvailabilityRequestService"
  sawsdl:modelReference="http://www.w3.org/2002/ws/sawsdl/spec/examples/taxonomy/POServiceClassification#ItemAvailabilityCheck">
    ...
</wsdl:interface>
    ...

Listing 2.1-2: Shows how a WSDL interface could be annotated with categorization information that could be used in publishing a Web service (for example, into a service registry)

2.2 Adding Categorization Information by Defining a Taxonomy

Some taxonomies may not provide direct URIs for their categories and may require multiple pieces of information to identify the categories.In such a case, users can define such information as per the requirements and associate a modelReference to point to such user-defined taxonomic information. For example, if a particular taxonomy specifies three pieces of information namely, the name of the taxonomy, the specific categorization in the taxonomy and a unique code for that taxonomy, then, it can be defined as follows.

@prefix categorization: <http://www.w3.org/2002/ws/sawsdl/spec/examples/taxonomy/Categorization#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix xs: <http://www.w3.org/2001/XMLSchema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

  categorization:Category rdf:type rdfs:Class .
  categorization:hasValue rdf:type rdf:Property;
     rdfs:domain categorization:Category;
     rdf:range rdfs:Literal .
  categorization:usesTaxonomy rdf:type rdfs:Property;
     rdfs:domain categorization:Category;
     rdf:range xs:anyUri .

Listing 2.2-1: Schema for defining a taxonomy with specific properties. This scehma is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/taxonomy/Categorization.

Then, an instance such as the one below in listing 2.2-2 that adheres to the above schema in Listing 2.2-1 can be defined and either imported or inserted into the WSDL file whose interface (or operation) is to be annotated.

@prefix categorization: <http://www.w3.org/2002/ws/sawsdl/spec/examples/taxonomy/Categorization#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix xs: <http://www.w3.org/2001/XMLSchema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

  categorization:Category rdf:type "urn:Electronics" ;
     categorization:hasValue "443112" ;
     categorization:usesTaxonomy "http://naics.com/" .

Listing 2.2-2: An instance of a taxonomy defined using the schema defined in Listing 2.2-1.

The annotation can be associated with the interface of a Web service as follows.

<wsdl:interface name="CheckAvailabilityRequestService"
   sawsdl:modelReference="http://www.w3.org/2002/ws/sawsdl/spec/examples/taxonomy/Categorization#Electronics">
  ...
</wsdl:interface>

Listing 2.2-3: A WSDL excerpt showing how a wsdl:interface could be annotated with taxonomy information from the listing defined in Listing 2.2-2.

Using similar modelReference annotation operations within an interface can also be annotated. SAWSDL does not specify any relationship between the categorization information specified at the level of an interface and the one that is specified on an operation that is contained within that interface. The example in listing 2.2-4 below shows how an operation within a Web service interface could be annotated using the same 'categorization' scheme.

<wsdl:operation name="CheckAvailabilityRequestOperation"
  sawsdl:modelReference="http://www.w3.org/2002/ws/sawsdl/spec/examples/taxonomy/Categorization#Electronics"
  ...
</wsdl:operation>

Listing 2.2-4: A WSDL excerpt showing how a wsdl:operation could be annotated with taxonomy information from the listing defined in Listing 2.2-2.

2.3 Using Categorization Annotations to Publish a Service in a UDDI Registry

In this subsection, we discuss how one can use the categorization annotation information defined by using the mechanisms described in section 2 to publish Web services in a UDDI registry. This is provided as an example for illustrative purpose. One can use similar mechanisms to publish the Web services in registries or repositories other than UDDI.

Following the example in Listing 2.2-2, one can define taxonomy references to point to a specific category defined in, say, NAICS [NAICS] taxonomy that is registered in a UDDI registry as shown in listing 2.3-1. This information can then be reused when a service (such as the CheckItemAvailability Service whose interface definition is shown in Listing 2.2-3) is published in the UDDI registry. In the following example we use the NAICS taxonomy registered in UDDI.

@prefix categorization: <http://www.w3.org/2002/ws/sawsdl/spec/examples/taxonomy/Categorization#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

  categorization:Category rdf:type "urn:Electronics" ;
     categorization:hasValue "443112" ;
     categorization:usesTaxonomy "uddi:uddi.org:ubr:categorization:naics:2002" .

Listing 2.3-1: An instance of a taxonomy defined using the schema defined in Listing 2.2-1 that refers to NAICS taxonomy registered in UDDI registry.

To publish a Web service that is represented in SAWSDL in a UDDI registry, an automatic Web service publishing engine can dereference the taxonomy information from its interface and use that information to determine which category of what taxonomy in the registry to publish the service to. For example, when publishing the service in UDDI V3, a category bag can be created to classify the service using this information. Listing 2.3-2 below shows the UDDI categoryBag structure that could be created from the categorization information in Listing 2.3-1.

<categoryBag>
  <keyedReference
    tModelKey="uddi:uddi.org:ubr:categorization:naics:2002"
    keyName="Electronics"
    keyValue="443112"/>
</categoryBag>

Listing 2.3-2: UDDI Category bag structure derived from the taxonomy instance in Listing 2.3-1.

In this section we have discussed the usage of modelReference concepts on an interface and operation for associating categorization relation information for illustrative purposes. Users may choose to use modelReferences on interfaces and operations for associating other behavioral aspects with a servicel.

3. Defining Annotations for use in Matching and Composing Web services

One of the main motivations for SAWSDL specification is to provide mechanisms using which semantic annotations can be added to WSDL documents so that these semantics can be used to help automate the matching and composition of Web services. In this section we present some examples to show how to add such annotations for use during Web service interface matching and composition. First we present an example to illustrate the use of annotations in Web service interface matching.

3.1 Matching Web Service Interfaces using a Shared Ontology

Let's consider the the following scenario. A requestor would like to submit a request to verify the availability of an item from a preferred supplier. Say that this request is represented as a CheckAvailabilityRequest WSDL (introduced in Listing 1.2-1). Also suppose that a service provider has a service to offer that enables the requesters to check for the availability of items it offers. This is called CheckInventoryService and is also represented as a WSDL with the same name (also introduced in Listing 1.2-2). Specifically, the request WSDL codifies the inputs it can supply and the outputs it expects of an item availability check service by the service provider. The service WSDL specifies the interface of a service that allows requesters to check for the availability of an inventory item by exposing the inputs it requires in order to provide item availability confirmation. At a high level the service offered by the service provider should match the request. However, the differences in the vocabulary used by the two services to represent their interfaces may get in the way of making a match. For example, the term itemCode used by the requester and the term SKU (Stock Keeping Unit) used by the provider both are meant to uniquely identify the item in question. Also, the term qty used by the requester and the term numBundles used by the provider both in this context may refer to the number of items (in one case, it is the number of items being requested and in the other case, it is the number of items being offered). However, a matching engine may not have sufficient information to identify them as related terms unless explicitly specified. Semantic annotations, in cases such as these, could be quite helpful. In the simple case, if there were to be a common semantic model that one can use to annotate the WSDLs of the requester and the service provider as shown below (in Listings 3.1-1 and 3.1-2), then a semantic engine could use this information to match the two Web services. In this example, annotation is done using modelReference extensibility element defined in SAWSDL.

The WSDL excerpt shown below in listing 3.1-1 represents one of the ways of semantically annotating WSDL document of the request for checking item availability.

<wsdl:description
  targetNamespace="http://org1.example.com/wsdl/CheckAvailabilityRequestService/"
  xmlns="http://org1.example.com/wsdl/CheckAvailabilityRequestService/"
  xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema"
  xmlns:sawsdl="http://www.w3.org/2002/ws/sawsdl/spec/sawsdl#"
  xmlns:SampleOntology="http://org1.example.com/ontologies/SampleOntology#">

  <wsdl:types>
    <xsd:schema targetNamespace="http://org1.example.com/wsdl/CheckAvailabilityRequestService">
    <xsd:element name="CheckAvailabilityRequestServiceRequest">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="itemCode" type="xsd:string"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntology#PartNumber"/>
          <xsd:element name="date" type="xsd:string"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntology#DueDate"/>
          <xsd:element name="qty" type="xsd:float"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntology#Quantity/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    <xsd:element name="CheckAvailabilityRequestServiceResponse" type="itemConfirmation"/>
    <xsd:simpleType name="itemConfirmation"
      sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntology#AvailabilityConfirmation">
      <xsd:restriction base="xsd:boolean"/>
    </xsd:simpleType>
    </xsd:schema>
  </wsdl:types>

  <wsdl:interface name="CheckAvailabilityRequestService">
      <wsdl:operation name="checkAvailabilityRequestOperation" pattern="http://www.w3.org/2006/01/wsdl/in-out">
      <wsdl:input element="CheckAvailabilityRequestServiceRequest"/>
      <wsdl:output element="CheckAvailabilityRequestServiceResponse"/>
    </wsdl:operation>
  </wsdl:interface>
</wsdl:description>

Listing 3.1-1: A WSDL excerpt of a semantically annotated service request that shows the usage of modelReference. This WSDL is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/SemannCheckAvailabilityRequestService.

The WSDL excerpt in listing 3.1-2 represents a way of semantically annotating the WSDL document of the service offered by the service provider for checking item availability.

<wsdl:description
  targetNamespace="http://org2.example.com/wsdl/CheckInventoryService/"
  xmlns="http://org2.example.com/wsdl/CheckInventoryService/"
  xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema"
  xmlns:sawsdl="http://www.w3.org/2002/ws/sawsdl/spec/sawsdl#"
  xmlns:SampleOntology="http://org1.example.com/ontologies/SampleOntology#">

  <wsdl:types>
    <xsd:schema targetNamespace="http://org2.example.com/wsdl/CheckInventoryService">
    <xsd:element name="CheckInventoryServiceRequest">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="SKU" type="xsd:string"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntology#SKU"/>
          <xsd:element name="deliveryDate" type="xsd:string"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntology#DueDate"/>
          <xsd:element name="numBundles" type="xsd:float"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntology#Quantity"/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    <xsd:element name="CheckInventoryServiceResponse">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="conf" type="xsd:boolean"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntology#AvailabilityConfirmation"/>
          <xsd:element name="numBundles_available" type="xsd:string"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntology#Quantity"/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    </xsd:schema>
  </wsdl:types>

  <wsdl:interface name="CheckInventoryService">
     <wsdl:operation name="checkInventoryOperation" pattern="http://www.w3.org/2006/01/wsdl/in-out">
       <wsdl:input element="CheckInventoryServiceRequest"/>
       <wsdl:output element="CheckInventoryServiceResponse"/>
    </wsdl:operation>
  </wsdl:interface>
</wsdl:description>

Listing 3.1-2: A WSDL excerpt of a semantically annotated service (advertisement) that shows the usage of modelReference. This example is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/SemannCheckInventoryService.

As can be noted, in this example both WSDL documents in this example are annotated with concepts from the same semantic model SampleOntology (shown in listing 3.1-3). In this example, the ontology contains the relationship between the concepts PartNumber and SKU i.e., a SKU Code is a subClassOf PartNumber. A semantic engine can infer this relationship during Web service interface matching by parsing and reasoning over this semantic model. Therefore, the WSDL elements 'itemCode' in the request WSDL and the 'SKU' in the service WSDL match with one another. In the case of the other input elements namely 'qty' vs 'numBundles' and 'date' vs 'deliveryDate', since both these sets of elements are annotated with shared semantic concepts namely 'Quantity' and 'DueDate' respectively the semantic ambiguity can be resolved by direct matching of semantic annotations. The same applies to matching outputs as well. The ontology that represents the subClassOf relationship between the two concepts PartNumber and SKU can be modeled in OWL as follows.

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix: <http://org1.example.com/ontologies/SampleOntology#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .

<http://org1.example.com/ontologies/SampleOntology#> rdf:type owl:Ontology .

  :PartNumber rdf:type owl:Class .
  :SKU rdf:type owl:Class;
    rdfs:subClassOf :PartNumber .
  :Quantity rdf:type owl:Class .
  :DueDate rdf:type owl:Class .
  :AvailabilityConfirmation rdf:type owl:Class .

Listing 3.1-3: A simple SampleOntology that captures the subClassOf relationship between PartNumber and SKU concepts. This sample ontology is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/ontologies/SampleOntology.n3.

3.2 Matching Web Service Interfaces with Ontology Mediation

In section 3.1 we made a shared ontology assumption between the requester and service provider domains. This assumption may not always hold good. The vocabulary differences may result in two different ontologies one for each side albeit for the same domain. In such a case one can create a mapping ontology by capturing the relationships between the concepts used in the different ontologies. Below we annoate the same two request and advertisement WSDLs using concepts from different ontologies. When a mapping ontology such as the one shown in Listing 3.2-3 is available, then the semantic annotations extracted from the request and the advertisement WSDL can be matched using such a mapping ontology.

The WSDL excerpt shown below in listing 3.2-1 represents one of the ways of semantically annotating WSDL document of the request for checking item availability.

<wsdl:description
  targetNamespace="http://org1.example.com/wsdl/CheckAvailabilityRequestService/"
  ....
  xmlns:Org1Ont="http://org1.example.com/ontologies/SampleOntologyOrg1#>

  <wsdl:types>
    <xsd:schema targetNamespace="http://org1.example.com/wsdl/CheckAvailabilityRequestService">
    <xsd:element name="CheckAvailabilityRequestServiceRequest">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="itemCode" type="xsd:string"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntologyOrg1#PartNumber"/>
          <xsd:element name="date" type="xsd:string"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntologyOrg1#DueDate"/>
          <xsd:element name="qty" type="xsd:float"
            sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntologyOrg1#Quantity/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    <xsd:element name="CheckAvailabilityRequestServiceResponse type="itemConfirmation"/>
    <xsd:simpleType name="itemConfirmation">
      sawsdl:modelReference="http://org1.example.com/ontologies/SampleOntologyOrg1#AvailabilityConfirmation"
      <xsd:restriction base:"xsd:boolean"/>
    </xsd:simpleType>
    </xsd:schema>
  </wsdl:types>

  <wsdl:interface name="CheckAvailabilityRequestService">
      <wsdl:operation name="checkAvailabilityRequestOperation" pattern="http://www.w3.org/2006/01/wsdl/in-out">
      <wsdl:input element="CheckAvailabilityRequestServiceRequest"/>
      <wsdl:output element="CheckAvailabilityRequestServiceResponse"/>
    </wsdl:operation>
  </wsdl:interface>
</wsdl:description>

Listing 3.2-1: A WSDL excerpt of a semantically annotated service request that shows the usage of modelReference. This WSDL is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/SemannCheckAvailabilityRequestService.

The WSDL excerpt shown below in Listing 3.2-2 represents a way of semantically annotating the WSDL document of the service offered by the service provider for checking item availability.

<wsdl:description
  targetNamespace="http://org2.example.com/wsdl/CheckInventoryService/"
  .....
  xmlns:Org2Ont="http://org2.example.com/ontologies/SampleOntologyOrg2#>

  <wsdl:types>
    <xsd:schema targetNamespace="http://org2.example.com/wsdl/CheckInventoryService">
    <xsd:element name="CheckInventoryServiceRequest">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="SKU" type="xsd:string"
            sawsdl:modelReference="http://org2.example.com/ontologies/SampleOntologyOrg2#SKU"/>
          <xsd:element name="deliveryDate" type="xsd:string"
            sawsdl:modelReference="http://org2.example.com/ontologies/SampleOntologyOrg2#DeliveryDate"/>
          <xsd:element name="numBundles" type="xsd:float"
            sawsdl:modelReference="http://org2.example.com/ontologies/SampleOntologyOrg2#NumBundles/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    <xsd:element name="CheckInventoryServiceResponse">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="conf" type="xsd:boolean"
           sawsdl:modelReference="http://org2.example.com/ontologies/SampleOntologyOrg2#AvailabilityConfirmation"/>
          <xsd:element name="numBundles_available" type="xsd:string"
            sawsdl:modelReference="http://org2.example.com/ontologies/SampleOntologyOrg2#NumBundles"/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    </xsd:schema>
  </wsdl:types>

  <wsdl:interface name="CheckInventoryService">
     <wsdl:operation name="checkInventoryOperation" pattern="http://www.w3.org/2006/01/wsdl/in-out">
       <wsdl:input element="CheckInventoryServiceRequest"/>
       <wsdl:output element="CheckInventoryServiceResponse"/>
    </wsdl:operation>
  </wsdl:interface>
</wsdl:description>

Listing 3.2-2: A WSDL excerpt of a semantically annotated service (advertisement) that shows the usage of modelReference. This WSDL is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/SemannCheckInventoryService.wsdl.

As noted, in this case the concepts originating from different ontologies represented in the two WSDLs shown above are mapped in a mapping ontology such as the one shown below in Listing 3.2-5. It contains relationships between concepts such as Quantity & NumBundles and Due Date & DeliveryDate and PartNumber & SKU. Just as in the example in section 3.1, a semantic matching engine can now be applied to reason over these relationships during Web service interface matching. The relationships between the concepts in this mapping ontology are shown pictorially in Figure 1 below.

Below, we list the three ontologies that are used in matching the checkAvailabilityRequest() request WSDL with the checkInventoryService() advertisement WSDL. The first ontology shown in listing 3.2-3 is the one used by the requesting organization (referred to using the name space http://org1.example.com/ontologies/SampleOntology) that defined the checkAvailabilityRequest() request WSDL. The second ontology shown in Listing 3.2-4 is the one used by the service advertising organization (referred to using the namespace ) that defined the checkInventoryService() advertisement WSDL. The third one shown in listing 3.2-5 is the mapping ontology defined by a third organization (could possibly be defined by either of the first two organizations as well) that relates the concepts from the two ontologies defined by org1 and org2.

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix: <http://org1.example.com/ontologies/SampleOntologyOrg1#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .

  <http://org1.example.com/ontologies/SampleOntologyOrg1#> rdf:type owl:Ontology  .

  :PartNumber rdf:type owl:Class .
  :DueDate rdf:type owl:Class .
  :Quantity rdf:type owl:Class .
  :AvailabilityConfirmation rdf:type owl:Class .

Listing 3.2-3:An RDF Turtle excerpt of an Ontology used by the organization that defined checkAvailabilityRequest() request WSDL. This ontology is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/ontologies/SampleOntologyOrg1.n3.

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix: <http://org2.example.com/ontologies/SampleOntologyOrg2#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .

  <http://org2.example.com/ontologies/SampleOntologyOrg2#> rdf:type owl:Ontology  .

  :SKU rdf:type owl:Class .
  :DeliveryDate rdf:type owl:Class .
  :NumBundles rdf:type owl:Class .
  :AvailabilityConfirmation rdf:type owl:Class .
  

Listing 3.2-4:An RDF Turtle excerpt of Ontology used by the organization that defined checkInventoryService() advertisement WSDL. This ontology is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/ontologies/SampleOntologyOrg2.n3.

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix: <http://org3.example.com/ontologies/MappingOntology#> .
@prefix Org1Ont: <http://org1.example.com/ontologies/SampleOntologyOrg1#> .
@prefix Org2Ont: <http://org2.example.com/ontologies/SampleOntologyOrg2#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .

  <http://org3.example.com/ontologies/MappingOntology#> rdf:type owl:Ontology  .

  Org2Ont:SKU rdfs:subClassOf Org1Ont:PartNumber .
  Org2Ont:NumBundles owl:equivalentClass Org1Ont:Quantity .
  Org2Ont:DeliveryDate owl:equivalentClass Org1Ont:DueDate .
  Org2Ont:AvailabilityConfirmation owl:equivalentClass Org1Ont:AvailabilityConfirmation .

Listing 3.2-5: An RDF Turtle excerpt showing the mapping ontology mapping concepts from ontologies in Listings 3.2-3 and 3.2-4. This mapping ontology is used to match the request WSDL in Listing 3.2-1 with the advertisement WSDL in Listing 3.2-2. This ontology is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/ontologies/MappingOntology.n3.

It is to be noted that SAWSDL specifies mechanisms to annotate WSDLs but does not say anything about how these annotations are generated. These annotations can either be created manually or by tools that can infer relationships between the terms used in the WSDLs and those that are given in a semantic model. Also, SAWSDL does not say anything about how the semantic models themselves are created. Just like the creation of annotations, these semantic models can either be created manually by a human expert or generated automatically using ontology learning tools or by a combination of both.

In the next section, we extend the above item availability check example to show how semantic annotations added to a WSDL can be used to compose Web services.

3.3 Composing Web Services - A Simple Example

This section illustrates how semantic annotations can be used to compose Web services. The request and advertisement WSDLs to be considered in this scenario are the same as the ones shown in Listings 3.2-1 and 3.2-2 respectively. However, we introduce a variation to the mapping ontology from section 3.2. Suppose that in the item availability checking scenario that we have been discussing so far, the subClassOf relationship between the concepts PartNumber and SKU is unspecified in the ontology. In this case, the request checkAvailabilityRequest() would not match with the service checkInventoryService() because there is no relationship between PartNumber and SKU. Also, suppose that there is another Web service called PartNumber2SKULookup ( ) that can take a PartNumber as input and produce SKU as output (Listing 3.3-1). Say that a matching engine would be able to find this service in the appropriate category in a registry - in this case it would be in 'Utilities/LookupServices' category (because the modelReference on the operation of this service contains the categorization information. So, presumably a publishing agent/program would have placed this service in the appropriate category that is referred to by the modelReference URI). Say, also, that a mapping ontology such as the one shown in Listing 3.3-2 is available for the matching engine. Now, the service PartNumber2SKULookup() can be composed with checkInventoryService() to match the request checkAvailabilityRequest() as shown in Figure 2. This can be achieved by simply extracting the semantic annotations from the request, and all the advertisement WSDLs and using the relationships in the mapping ontology to match the corresponding concepts. A simple Web service composition using the semantics annotations on the request and advertisement services is illustrated in Figure 2.

<wsdl:description
  targetNamespace="http://org3.example.com/wsdl/PartNumber2SKULookupService/"
  xmlns="http://org3.example.com/wsdl/PartNumber2SKULookupService/"
  xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema"
  xmlns:sawsdl="http://www.w3.org/2002/ws/sawsdl/spec/sawsdl#"
  xmlns:Org3Ont="http://org3.example.com/ontologies/SampleOntologyOrg3#">

  <wsdl:types>
    <xsd:schema targetNamespace="http://org3.example.com/wsdl/PartNumber2SKULookupService">
      <xsd:element name="PartNumber2SKULookupServiceRequest" type="partNum"/>
      <xsd:simpleType name="partNum">
        sawsdl:modelReference="http://org3.example.com/ontologies/SampleOntologyOrg3#PartNumber">
        <xsd:restriction base="xsd:string"/>
      </xsd:simpleType>

      <xsd:element name="PartNumber2SKULookupServiceResponse" type="SKU"/>
      <xsd:simpleType name="SKU">
        sawsdl:modelReference="http://org3.example.com/ontologies/SampleOntologyOrg3#SKU">
        <xsd:restriction base="xsd:string"/>
      </xsd:simpleType>
    </xsd:schema>
  </wsdl:types>

  <wsdl:interface name="PartNumber2SKULookupService">
    <wsdl:operation name="PartNumber2SKULookupService" pattern="http://www.w3.org/2006/01/wsdl/in-out"
        sawsdl:modelReference="http://org3.example.com/taxonomies/Utilities#LookupServices">
        <wsdl:input element="PartNumber2SKULookupServiceRequest"/>
        <wsdl:output element="PartNumber2SKULookupServiceResponse"/>
    </wsdl:operation>
  </wsdl:interface>
</wsdl:description>

Listing 3.3-1: A WSDL excerpt representing PartNumber2SKULookup service. This WSDL is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/PartNumber2SKULookupService.

Listing 3.3-2 below shows the variation on the mapping ontology discussed in section 3.2. As noted, this ontology does not contain any relationship between PartNumber and SKU concepts. The additional differences from Listing 3.2-5 are shown below in bold font style. In this example, we assume that the same organization that provides the PartNumber2SKULookupService() provides the mapping ontology. In practice, this does not have to be the case. Any of the three organizations (org1, org2, and org3 referred to in the namespaces) or an entirely new organization (org4) can provide a mapping ontology. The namespaces, in such a case, should reflect the change accordingly. The ontologies that are used to annotate the request WSDL checkAvailabilityRequest() and the advertisement WSDL checkInventoryService() are unchanged from those presented in Listing 3.2-3 and 3.2-4.

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix: <http://org1.example.com/ontologies/MappingOntology#> .
@prefix Org1Ont: <http://org1.example.com/ontologies/SampleOntologyOrg1#> .
@prefix Org2Ont: <http://org2.example.com/ontologies/SampleOntologyOrg2#> .
@prefix Org3Ont: <http://org3.example.com/ontologies/SampleOntologyOrg3#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .

  <http://org3.example.com/ontologies/MappingOntology#> rdf:type owl:Ontology  .

  Org2Ont:NumBundles rdf:type owl:Class;
     owl:equivalentClass Org1Ont:Quantity .
  Org2Ont:DeliveryDate rdf:type owl:Class;
     owl:equivalentClass Org1Ont:DueDate .
  Org2Ont:AvailabilityConfirmation rdf:type owl:Class;
     owl:equivalentClass Org1Ont:AvailabilityConfirmation .

  Org3Ont:PartNumber rdf:type owl:Class;
     owl:equivalentClass Org1Ont:PartNumber .
  Org3Ont:SKU rdf:type owl:Class;
     owl:equivalentClass Org2Ont:SKU .
 

Listing 3.3-2: Revised Mapping Ontology that contains relationships between concepts from three different ontologies. This ontology is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/ontologies/RevisedMappingOntology.n3.

3.4 Composing Web Services using Ontology Reasoning

We introduce three variations to our item availability checking scenario in this section to illustrate how one can use semantic annotations to compose Web services with ontology reasoning. First, suppose that we have a checkInventoryService() that takes an UPC as input inplace of SKU ((as introduced in Listing 1.2-2 but with semantic annotations as in Listing 3.4-1 below). Then, this service will not match the request checkAvailabilityRequest() (unchanged from Listing 3.2-1) because there is no relationship between the concepts PartNumber and UPC in the mapping ontology. So, even semantic annotations will not be able to help in matching the request checkAvailabilityRequest() and the advertisement checkInventoryService(). Second, say that there is another Web service called SKU2UPCLookup( ) that can take an SKU as input and produce UPC (Universal Product Code) as output (Listing 3.4-2). Third, the original mapping ontology introduced in Listing 3.2-3 has an addition of UPC concept. But it is to be noted that the ontology does not specify any relationship between SKU and UPC codes. Figure 3 summarizes the relationships between the concepts PartNumber, SKU, and UPC in SampleOntology. Now with these three variations, we have enough information to see how a semantic engine can compose Web services to match the request checkAvailabilityRequest() with checkInventoryService().

<wsdl:description
  targetNamespace="http://org2.example.com/wsdl/CheckInventoryService/"
  ....
  xmlns:Org2Ont="http://org2.example.com/ontologies/SampleOntologyOrg2#">

  <wsdl:types>
    <xsd:schema targetNamespace="http://org2.example.com/wsdl/CheckInventoryService">
    <xsd:element name="CheckInventoryServiceRequest">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="UPC" type="xsd:string"
            sawsdl:modelReference="http://org2.example.com/ontologies/SampleOntologyOrg2#UPC"/>
          <xsd:element name="deliveryDate" type="xsd:string"
            sawsdl:modelReference="http://org2.example.com/ontologies/SampleOntologyOrg2#DeliveryDate"/>
          <xsd:element name="numBundles" type="xsd:float"
            sawsdl:modelReference="http://org2.example.com/ontologies/SampleOntologyOrg2#NumBundles"/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    <xsd:element name="CheckInventoryServiceResponse">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="conf" type="xsd:boolean"
            sawsdl:modelReference="http://org2.example.com/ontologies/SampleOntologyOrg2#AvailabilityConfirmation"/>
          <xsd:element name="numBundles_available" type="xsd:string"
            sawsdl:modelReference="http://org2.example.com/ontologies/SampleOntologyOrg2#NumBundles"/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    </xsd:schema>
  </wsdl:types>

  <wsdl:interface name="CheckInventoryService">
     <wsdl:operation name="checkInventoryOperation" pattern="http://www.w3.org/2006/01/wsdl/in-out">
       <wsdl:input element="CheckInventoryServiceRequest"/>
       <wsdl:output element="CheckInventoryServiceResponse"/>
    </wsdl:operation>
  </wsdl:interface>
</wsdl:description>

Listing 3.4-1: CheckInventoryService() WSDL excerpt with a variation where the input SKU is replaced by UPC for the purpose of illustrating Web service composition with ontology reasoning. This example is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/SemannCheckInventoryService2.

A WSDL excerpt of SKU2UPCLookupService() is shown below.

<wsdl:description
  targetNamespace="http://org3.example/com/wsdl/SKU2UPCLookupService/"
  .....
  xmlns:Org3Ont="http://org3.example.com/ontologies/SampleOntologyOrg3#">

  <wsdl:types>
    <xsd:schema targetNamespace="http://org3.example.com/wsdl/SKU2UPCLookupService">
      <xsd:element name="SKU2UPCLookupServiceRequest" type="SKU"/>
      <xsd:simpleType name="SKU">
        sawsdl:modelReference="http://org3.example.com/ontologies/SampleOntologyOrg3#SKU">
        <xsd:restriction base="xsd:string"/>
      </xsd:simpleType>

      <xsd:element name="SKU2UPCLookupServiceResponse" type="UPC"/>
      <xsd:simpleType name="UPC">
        sawsdl:modelReference="http://org3.example.com/ontologies/SampleOntologyOrg3#UPC">
        <xsd:restriction base="xsd:string"/>
      </xsd:simpleType>
    </xsd:schema>
  </wsdl:types>

  <wsdl:interface name="SKU2UPCLookupService">
    <wsdl:operation name="SKU2UPCLookupService" pattern="http://www.w3.org/2006/01/wsdl/in-out"
        sawsdl:modelReference="http://org3.example.com/taxonomies/Utilities#LookupServices">
        <wsdl:input element="SKU2UPCLookupServiceRequest"/>
        <wsdl:output element="SKU2UPCLookupServiceResponse"/>
    </wsdl:operation>
  </wsdl:interface>
</wsdl:description>

Listing 3.4-2: A WSDL excerpt representing SKU2UPCLookup service. This WSDL is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/SKU2UPCLookupService.

Below, we list the three ontologies that are used in matching the checkAvailabilityRequest() request WSDL with the checkInventoryService() advertisement WSDL according to the scenario described in this section. The first ontology shown in Listing 3.4-3 is the one used by the requesting organization (referred to using the name space http://org1.example.com/ontologies/SampleOntologyOrg1) that defined the checkAvailabilityRequest() request WSDL. Please note that this differs from the Listing in 3.2-3 because this ontology contains the 'subClassOf' relationship between SKU and PartNumber concepts. The second ontology shown in Listing 3.4-4 is the one used by the service advertising organization (referred to using the namespace ) that defined the checkInventoryService() advertisement WSDL. Please note that this differs from the Listing in 3.2-4 because this contains the concept UPC instead of SKU. The third one shown in Listing 3.2-5 is the mapping ontology defined by a third organization (could possibly be defined by either of the first two organizations as well) that relates the concepts from the two ontologies defined by org1 and org2.

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix: <http://org1.example.com/ontologies/SampleOntologyOrg1#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .

  <http://org1.example.com/ontologies/SampleOntologyOrg1#> rdf:type owl:Ontology  .

  :PartNumber rdf:type owl:Class .
  :SKU rdf:type owl:Class;
    rdfs:subClassOf :PartNumber .
  :DueDate rdf:type owl:Class .
  :Quantity rdf:type owl:Class .
  :AvailabilityConfirmation rdf:type owl:Class .

Listing 3.4-3:An RDF Turtle excerpt of an Ontology used by the organization that defined checkAvailabilityRequest() request WSDL. This ontology is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/ontologies/SampleOntologyOrg1.n3.

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix: <http://org2.example.com/ontologies/SampleOntologyOrg2#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .

  <http://org2.example.com/ontologies/SampleOntologyOrg2#> rdf:type owl:Ontology  .

  :UPC rdf:type owl:Class;
  :DeliveryDate rdf:type owl:Class .
  :NumBundles rdf:type owl:Class .
  :AvailabilityConfirmation rdf:type owl:Class .
  

Listing 3.4-4: An RDF Turtle excerpt of Ontology used by the organization that defined checkInventoryService() advertisement WSDL. This ontology is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/ontologies/SampleOntologyOrg2.n3.

Listing 3.4-5 represents the updated sample ontology that enables composition in this example. It relates the concepts in the ontologies shown in Listings 3.4-3 and 3.4-4. Note that the ontology as such does not specify any relationship between SKU and UPC. Given an SKU, its corresponding UPC code is retrieved by the Web service SKU2UPCLookup(). Here also, we assume that the organization that is providing the SKU2UPCLookupService() is providing the mapping ontology as well. As mentioned earlier in section 3.3, this does not always have to be the case.

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix: <http://org1.example.com/ontologies/MappingOntology#> .
@prefix Org1Ont: <http://org1.example.com/ontologies/SampleOntologyOrg1#> .
@prefix Org2Ont: <http://org2.example.com/ontologies/SampleOntologyOrg2#> .
@prefix Org3Ont: <http://org3.example.com/ontologies/SampleOntologyOrg3#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .

  <http://org3.example.com/ontologies/MappingOntology#> rdf:type owl:Ontology  .

  Org2Ont:NumBundles owl:equivalentClass Org1Ont:Quantity .
  Org2Ont:DeliveryDate owl:equivalentClass Org1Ont:DueDate .
  Org2Ont:AvailabilityConfirmation owl:equivalentClass Org1Ont:AvailabilityConfirmation .

  Org3Ont:SKU rdf:type owl:Class;
     owl:equivalentClass Org1Ont:SKU .
  Org3Ont:UPC rdf:type owl:Class;
     owl:equivalentClass Org2Ont:UPC . 

Listing 3.4-5: Revised Mapping Ontology that contains relationships between concepts PartNumber, SKU, and UPC among other things that is used in this section to illustrate Web service composition using ontology reasoning. This ontology is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/ontologies/RevisedMappingOntology.n3.

Figure 3 represents an altered version of the ontology that enables composition in this example.

Figure 4 shows how Web service composition can be achieved by using the semantic annotations in the WSDL files discussed in this example. As can be noted, in this scenario, a semantic engine retrieves the semantic annotations from checkAvailabilityRequest() for element itemCode namely PartNumber and for the element SKU in SKU2UPCLookup() service namely SKU. The annotation PartNumber doesnot match lexically with the concept SKU. So, the semantic engine could then consult the MappingOntology to see if there is any relationship between PartNumber and SKU. The ontology reasoner can return the existance of 'subClassOf' relationship between SKU and PartNumber. This information can then be used in composing SKU2UPCLookup() with CheckInventoryService() as shown in Figure 4 to match the request CheckAvailabilityRequest(). Again, as mentioned earlier in Section 3.3, a matching engine would be able to find a utility service such as SKU2UPCLookup() in the appropriate category in a registry - in this case it would be in 'Utilities/LookupServices' category because the modelReference on the operation of this service contains the categorization information. So, presumably a publishing agent/program would have placed this service in the appropriate category that is referred to by the modelReference URI.

The example presented in this section was a variation of the one discussed in section 3.4. It illustrated how Web service composition can be achieved usng the relationships between concepts in an ontology even when the semantic annotations on the services don't match directly.

3.5 Matching Using Multiple Annotations

SAWSDL allows multiple annotations to be associated with those WSDL elements that can have a modelReference extension. These annotations could be pointing to different concepts from the same semantic model or from different models altogether. For example, a WSDL element with the name itemCode can be associated with SampleOntology#PartNumber and SampleOntology#SKU concepts. SAWSDL does not specify any relationship between these multiple annotations other than saying that they all apply. It is upto the consumers of these annotated WSDLs to use the ones that are relevant to them or to figure out the relationship between the concepts, if they so choose, by consulting the ontology that defines them. The following example in Listing 3.5-1 shows the annotation of itemCode with multiple annotations. If a requesting WSDL is annotated with multiple concepts like shown in Listing 3.5-1, this increases the likelihood of matching this request with other advertisement/service WSDLs. Similarly, if a service WSDL is annotated with multiple concepts, possibly more request WSDLs will match it.

  ...
<xsd:simpleType name="itemCode"
  sawsdl:modelReference="http://org3.example.com/ontologies/SampleOntologyOrg3#PartNumber
                 http://org3.example.com/ontologies/SampleOntologyOrg3#SKU"/>
  <xsd:restriction base="xsd:string"/>
</xsd:simpleType>
...

Listing 3.5-1: A WSDL excerpt showing multiple annotations to a simple type

The example given in this section so far illustrated multiple annotations that come from the same ontology. It is possible for elements to be annotated with concepts from different ontologies as well. The mechanism for doing so is exactly the same as the one employed in Listing 3.5-1 except in the latter case, the namespaces for the concepts coming from different ontolgies would be different.

3.6 Matching Using Complex Type Annotations

In the examples that we discussed so far, all annotations are added at the member element levels of a complex type. SAWSDL allows annotations to be added either at the complex type level (top level) or at the member element level (bottom level) or both. In cases where both complex type and the member elements have annotations, SAWSDL does not specify any relationship between the modelReferences on a complex type and those on the elements contained within a complex type. The listing below (Listing 3.6-1) illustrates the usage of modelReference for annotating the complex type 'ItemRequest' as well as the member elements.

<wsdl:types>
  ...
  <xsd:element name="ItemRequest"
    sawsdl:modelReference="http://org3.example.com/ontologies/SampleOntologyOrg3#OrderItem">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:element name="itemCode" type="xsd:string"/>
        <xsd:element name="date" type="xsd:string"/>
        <xsd:element name="qty" type="xsd:string"/>
       </xsd:sequence>
    </xsd:complexType>
  </xsd:element>
  ...
</wsdl:types>

Listing 3.6-1: WSDL excerpt from CheckAvailabilityRequest() showing the annotation of a complexType.

Here is one possible way in which the annotation on a complex type can be used. The annotation on the complex type 'itemRequest' such as the one in Listing 3.6-1 which is part of checkAvailabilityRequest() can be used to match another complex type such as the one in checkInventoryService() shown in Listing 3.6-2 below. The annotation on a complex type can be used a first level of matching in structure matching i.e., a semantic matching engine could use these annotations to see if two complex types have any relationship at all. If they do, perhaps spending more time on matching the member elements of complex types may be worth the time. If not, perhaps there is no need to do detailed matching of complex structures. Therefore, the annotations on complex types can be used for first level of structure matching.

 <wsdl:types>
  ...
    <xsd:element name="Item"
      sawsdl:modelReference="http://org3.example.com/ontologies/SampleOntologyOrg3#OrderItem">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="SKU" type="xsd:string"/>
          <xsd:element name="deliveryDate" type="xsd:string"/>
          <xsd:element name="numBundles" type="xsd:float"/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
   ...
 </wsdl:types>

Listing 3.6-2: WSDL excerpt from CheckInventoryService() showing the annotation of a compex type.

So far, we have discussed how to annotate WSDL documents with semantic concepts for use in Web service discovery, matching and composition.These annotations that can be added to a WSDL using modelReferences are meant to add semantic clarity to WSDL elements by pointing to concepts in a semantic model that describes the larger context. They help understand whether a service matches clients' requests at a semantic level. However, there may still be mismatches at the data level that would need to be addressed and captured to enable the invocation of a Web service. In the following section, we discuss the mechanisms defined in SAWSDL to capture such data transformation maps (knowns as schema mappings) to enable Web service invocation.

3.7 Representing Conditions

The modelReference attribute can be used to represent behavioral constraints related with services. For example, in the purchase order scenario, if we were to add constraints as shown below related to shipping details, they can be represented in SAWSDL using modelReferences as shown in Listing 3.7-1.

• Only packages weighing 50 lbs or less can be shipped
• Shipping is possible only in North America, and Europe.
• Delivery is possible only between 7am and 8pm.
• Delivery has to be ordered at least 2 working days in advance.

In Listing 3.7-1, shipping details are shown in SWRL language.

Implies (Antecedent (
                      swrlb:substract (2 I-variable(deliveryDay) I-variable(orderDay))
                      I-variable(hour) swrlb:greaterThanOrEqual 7
                      I-variable(hour) swrlb:lessThanOrEqual 20
                      I-variable(continent) swrlb:equal (http://en.wikipedia.org/wiki/North_america)
                      I-variable(weight) swrlb:lessThanOrEqual 50
                    )
        Consequent (shipment(I-variable(package) OK))
Implies (Antecedent (
                      swrlb:substract (2 I-variable(deliveryDay) I-variable(orderDay))
                      I-variable(hour) swrlb:greaterThanOrEqual 7
                      I-variable(hour) swrlb:lessThanOrEqual 20
                      I-variable(continent) swrlb:equal (http://en.wikipedia.org/wiki/Europe)
                      I-variable(weight) swrlb:lessThanOrEqual 50
                    )
        Consequent (shipment(I-variable(package) OK))

Listing 3.7-1: A SWRL represention of the rules as described above. This example is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/rule/swrl.swrl.

<wsdl:description
  targetNamespace="http://org1.example.com/wsdl/CheckAvailabilityRequestService/"
  xmlns="http://org1.example.com/wsdl/CheckAvailabilityRequestService/"
  xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <wsdl:types>
   <xsd:schema targetNamespace=http://org1.example.com/wsdl/CheckAvailabilityRequestService">
    <xsd:element name="CheckAvailabilityRequestServiceRequest">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="itemCode" type="xsd:string"/>
          <xsd:element name="date" type="xsd:string"/>
          <xsd:element name="qty" type="xsd:float"/>
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>
    <xsd:element name="CheckAvailabilityRequestServiceResponse" type="itemConfirmation"/>
    <xsd:simpleType name="itemConfirmation" 
        sawsdl:modelReference="http://www.w3.org/2002/ws/sawsdl/spec/examples/rule/swrl.swrl"> 
      <xsd:restriction base="xsd:boolean"/>
    </xsd:simpleType>
    </xsd:schema>
  </wsdl:types>

 <wsdl:interface name="CheckAvailabilityRequestService">
   <wsdl:operation name="CheckAvailabilityRequestOperation" pattern="http://www.w3.org/2006/01/wsdl/in-out">
   <wsdl:input element="CheckAvailabilityRequestServiceRequest"/>
   <wsdl:output element="CheckAvailabilityRequestServiceResponse"/>
    </wsdl:operation>
  </wsdl:interface>
 </wsdl:description>

Listing 3.7-2: An example showing the usage of modelReference to represent conditions

4. Defining Schema Mappings to Enable Web Service Invocation

Consider the example where a client/requester may have a 'first name' and 'last name' among its data as shown in Listing 4-1 and the advertisement service requires a 'full name' as shown in Listing 4-2. In this case, when the client invokes the Web service of the service provider, the data values of firstName and lastName need to be concatenated in the message to the advertisement Web service to pass the correct values for the fullName element.

..
  <xsd:element name="firstName" type=xsd:string/>
  <xsd:element name="lastName" type=xsd:string/>
..

Listing 4-1: An XML excerpt showing two elements firstName and lastName.

..
  <xsd:element name="Name" type=xsd:string/>
 ..

Listing 4-2: An XML excerpt showing an element Name.

To facilitate the association of such types of data transformations with Web services, SAWSDL provides a mechanism called schemaMapping. A schemaMapping concept is provided to allow the specification of transformation functions on the WSDL elements to map instance data defined by that XML schema document to the semantic data of the concepts in a semantic model. Conversely, it allows the specification of transformation functions that map the semantic data of ontological concepts to the instance data values that adheres to the XML schema document that is being annotated. In the former case, the transformation functions are referred to using the extensibility attribute liftingSchemaMapping and in the latter case it is called loweringSchemaMapping. These kinds of mappings are useful in general when the structure of the instance data does not correspond directly to the organization of the semantic data. Also, these types of mappings can be used to generate mediation code to support invocation of a Web service.

In the remaining part of this section, we illustrate this lifting and lowering schema mappings in the context of a purchase order scenario. We use XSLT [XSLT] as the mapping language for illustrative purposes. SAWSDL specification by itself does not prescribe any specific mapping language. Users can choose a mapping language of their choice. The purchase order scenario is very similar to the check availability scenario we have been discussing throughout this document so far.

4.1 Lifting Schema Mapping

A liftingSchemaMapping takes as input XML data (that adheres to a given XML schema) and produces semantic data (that adheres to an RDF ontology) as output. Let us consider purchase order scenario. Listing 4.1-1 shows excerpts of a WSDL that has OrderRequest, item and OrderResponse complex types. Say that we would like to specify a lifting schema mapping notion on OrderRequest complex type so that an XML instance of an OrderRequest complex type can be mapped with the semantic data in the RDF graph shown in Listing 4.1-2. Then, we would specify OrderRequest2Ont.xslt as a lifting schema mapping notion on OrderRequest concept as shown in Listing 4.1-1 below.

<wsdl:description>
  ...
  <wsdl:types>
  <xsd:schema
    targetNamespace="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/PurchaseOrderService#" elementFormDefault="qualified">

    <xsd:element name="OrderRequest">
      <xsd:complexType sawsdl:liftingSchemaMapping="http://www.w3.org/2002/ws/sawsdl/spec/examples/mapping/OrderRequest2Ont.xslt">
        <xsd:sequence>
          <xsd:element name="firstName" type="xsd:string"/>
          <xsd:element name="lastName" type="xsd:string"/>
          <xsd:element name="item" type="item" minOccurs="1" maxOccurs="unbounded" />
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>

    <xsd:complexType name="item">
      <xsd:all>
        <xsd:element name="itemCode" type="xsd:string"/>
        <xsd:element name="quantity" type="xsd:float"/>
        <xsd:element name="dueDate" type="xsd:string"/>
        <xsd:element name="billingInfo" type="xsd1:POBilling"/>
      </xsd:all>
    </xsd:complexType>

    <xsd:element name="OrderResponse" type="Confirmation"/>
    <xsd:simpleType name="Confirmation">
      <xsd:restriction base="xsd:string">
        <xsd:enumeration value="Confirmed"/>
        <xsd:enumeration value="Pending"/>
        <xsd:enumeration value="Rejected"/>
      </xsd:restriction>
    </xsd:simpleType>
  </xsd:schema>
  </wsdl:types>

  <wsdl:interface name="Order">
    <wsdl:operation name="order" pattern="http://www.w3.org/2006/01/wsdl/in-out">
      <wsdl:input element="OrderRequest"/>
      <wsdl:output element="OrderResponse"/>
    </wsdl:operation>
  </wsdl:interface>
</wsdl:description>
  ...

Listing 4.1-1: A WSDL excerpt showing liftingSchemaMapping notion. This example is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/PurchaseOrderService.

Listing 4.1-1 refers to http://www.w3.org/2002/ws/sawsdl/spec/examples/mapping/OrderRequest2Ont.xslt. This XSLT maps the elements of OrderRequest complex type with the corresponding ones in the ontology shown in 4.1-2.

@prefix xs: <http://www.w3.org/2001/XMLSchema#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix : <http://org1.example.com/ontologies/PurchaseOrder#> .

  <http://org1.example.com/ontologies/PurchaseOrder#> rdf:type owl:Ontology .

  :OrderRequest rdf:type owl:Class .
  :hasLineItems rdf:type owl:ObjectProperty ;
      rdfs:domain :OrderRequest ;
      rdfs:range :LineItem .
  :LineItem rdf:type owl:Class .
  :hasPart rdf:type owl:ObjectProperty , owl:FunctionalProperty ;
      rdfs:domain :LineItem ;
      rdfs:range :Part .
  :Part rdf:type owl:Class .
  :hasPartCode rdf:type owl:ObjectProperty ;
      rdfs:domain :Part ;
      rdfs:range :PartNum .
  :PartNum rdf:type owl:Class .
  :hasLexicalRespresentation rdf:type  owl:DatatypeProperty , owl:FunctionalProperty ;
      rdfs:domain
              [ rdf:type owl:Class ;
                owl:unionOf (:Name :PartNum :Date)
              ] ;
      rdfs:range xs:string .
  :hasDueDate rdf:type owl:ObjectProperty ;
      rdfs:domain :LineItem ;
      rdfs:range :Date .
  :Date rdf:type owl:Class .
  :hasQuantity rdf:type owl:DatatypeProperty ;
      rdfs:domain :LineItem ;
      rdfs:range xs:float .
  :hasBillingInfo rdf:type owl:DatatypeProperty ;
      rdfs:domain :LineItem ;
      rdfs:range xsd1:billingInfo .
  :hasCustomer rdf:type owl:ObjectProperty , owl:FunctionalProperty ;
      rdfs:domain :OrderRequest ;
      rdfs:range :Customer .
  :Customer rdf:type owl:Class .
  :hasCustomerName  rdf:type owl:ObjectProperty ;
      rdfs:domain :Customer ;
      rdfs:range :Name .
  :Name rdf:type owl:Class .

Listing 4.1-2: A PurchaseOrder ontology in RDF turtle format. This ontology is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/ontologies/PurchaseOrder.n3.

Given a OrderRequest message (as shown in Listing 4.1-3) which corresponds to the schema in Listing 4.1-1, the part where an XSLT would be of most value in this example is where the values of firstName and lastName are concatenated to match with the semantic data of the concept 'Name' in the PurchaseOrder Ontology. An excerpt of such a transformation in XSLT is shown in Listing 4.1-4 below.

<OrderRequest
  xmlns="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/PurchaseOrderService#">

  <firstName>John</firstName>
  <lastName>Smith</lastName>
  <item>
    <itemCode>052053811</itemCode>
    <quantity>12.0</quantity>
    <dueDate>20061114</dueDate>
    <billingInfo>88 Park Road, Lower Dangan, Galway, Ireland</billingInfo>
  </item>
  <item>
    <itemCode>45001113</itemCode>
    <quantity>10.0</quantity>
    <dueDate>20061224</dueDate>
    <billingInfo>70 Sandyhill Road, Shalthill, Galway, Ireland</billingInfo>
  </item>
</OrderRequest>

Listing 4.1-3: An excerpts of XML data that adheres to the WSDL in Listing 4.1-1.

<!DOCTYPE rdf:RDF
    [<!ENTITY xs "http://www.w3.org/2001/XMLSchema#">
     <!ENTITY xsd1 "http://www.w3.org/2001/XMLSchema#">
    ]
>

<xsl:transform version="2.0"
  xmlns:order="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/PurchaseOrderService#"
    xmlns:po="http://org1.example.com/ontologies/PurchaseOrder#"
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:owl="http://www.w3.org/2002/07/owl#">

  <xsl:output method="xml" version="1.0" encoding="iso-8859-1" indent="yes" />
  <xsl:template match="/order:OrderRequest">
    <rdf:RDF>
      <owl:Ontology/>
      <po:OrderRequest>
        <po:hasCustomer>
          <po:Customer>
            <po:hasCustomerName>
              <po:name>
                <po:hasLexicalRepresentation>
                  <xsl:value-of select="concat(
                    order:firstName,
                    ' ',
                    order:lastName)"/>
                </po:hasLexicalRepresentation>
              </po:name>
            </po:hasCustomerName>
          </po:Customer>
        </po:hasCustomer>
        <po:hasLineItems>
          <po:lineItem>
            <po:hasPart>
              <po:part>
                <po:hasPartCode>
                  <po:partNum>
                    <po:hasLexicalRepresentation>
                      <xsl:value-of select="order:item/order:itemCode"/>
                    </po:hasLexicalRepresentation>
                  </po:partNum>
                </po:hasPartCode>
              </po:part>
            </po:hasPart>
            <po:hasDueDate>
              <po:date>
                <po:hasLexicalRepresentation>
                  <xsl:value-of select="order:item/order:dueDate"/>
                </po:hasLexicalRepresentation>
              </po:date>
            </po:hasDueDate>
            <po:hasQuantity rdf:datatype="&xs;float">
              <xsl:value-of select="order:item/order:quantity"/>
            </po:hasQuantity>
            <po:hasBillingInfo rdf:datatype="&xsd1;POBilling">
              <xsl:value-of select="order:item/order:billingInfo"/>
            </po:hasBillingInfo>
          </po:lineItem>
          <xsl:apply-templates select="order:OrderRequest" />
        </po:hasLineItems>
      </po:OrderRequest>
      </rdf:RDF>
    </xsl:template>
</xsl:transform> 

Listing 4.1-4: An XSLT excerpt that concatenates the values of firstName and lastName elements to form the semantic data of the concept FullName in the ontology. This example is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/mapping/OrderRequest2Ont.

A sample semantic data that is obtained by applying XSLT in Listing 4.1-3 to WSDL in Listing 4.1-1 is shown in Listing 4.1-4.

<!DOCTYPE rdf:RDF[
    <!ENTITY xs  "http://www.w3.org/2001/XMLSchema#" >
]
> <rdf:RDF
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:owl="http://www.w3.org/2002/07/owl#"
  xmlns="http://org1.example.com/ontologies/PurchaseOrder#"
  xml:base="http://org1.example.com/ontologies/PurchaseOrder#">

  <owl:Ontology />
  <OrderRequest>
    <hasLineItems>
      <LineItem>
        <hasPart>
          <part>
            <hasPartCode>
              <partNum>
                <hasLexicalRespresentation>052053811</hasLexicalRespresentation>
              </partNum>
            </hasPartCode>
          </part>
        </hasPart>
        <hasDueDate>
          <date>
            <hasLexicalRespresentation>20061114</hasLexicalRespresentation>
          </date>
        </hasDueDate>
        <hasQuantity rdf:datatype="&xs;float">12.0</hasQuantity>
        <hasBillingInfo rdf:datatype="&xsd1;POBilling">88 Park Road, Lower Dangan, Galway, Ireland</hasBillingInfo>
      </LineItem>
    </hasLineItems>
    <hasCustomer>
      <Customer>
        <hasCustomerName>
          <Name>
            <hasLexicalRespresentation>John Smith</hasLexicalRespresentation>
          </Name>
        </hasCustomerName>
      </Customer>
    </hasCustomer>
  </OrderRequest>
</rdf:RDF> 

Listing 4.1-5: An excerpt of semantic data that adheres to the variation on SampleOntology. This example is also available at: http://www.w3.org/2002/ws/sawsdl/spec/examples/ontologies/OrderRequest.

<xsd:element name="OrderRequest">
      <xsd:complexType sawsdl:liftingSchemaMapping="http://www.w3.org/2002/ws/sawsdl/spec/examples/mapping/OrderRequest2Ont.xslt
          sawsdl:loweringSchemaMapping="http://www.w3.org/2002/ws/sawsdl/spec/examples/mapping/Ont2OrderRequest#lowering"">
        <xsd:sequence>
          <xsd:element name="firstName" type="xsd:integer">John</xsd:element>
          <xsd:element name="lastName" type="xsd:integer">Smith</xsd:element>
          <xsd:element name="item" type="item" minOccurs="1" maxOccurs="unbounded" />
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>

<lowering>
  <sparqlQuery>
    PREFIX po: <http://org1.example.com/ontologies/PurchaseOrder#>
    SELECT ?name ?partNum ?quantity ?dueDate ?billingInfo
    WHERE {
      ?order po:hasCustomer ?customer .
        ?customer po:hasCustomerName ?custName .
          ?custName po:hasLexicalRespresentation ?name .
      ?order po:hasLineItems ?item .
        ?item po:hasQuantity ?quantity .
        ?item po:hasBillingInfo ?billingInfo .
        ?item po:hasDueDate ?Date .
          ?date po:hasLexicalRepresentation ?dueDate .
        ?item po:hasPart ?part .
          ?part po:hasPartCode ?code .
            ?code po:hasLexicalRespresentation ?partNum }
  </sparqlQuery> 

<sparql xmlns="http://www.w3.org/2005/sparql-results#">
  <head>
    <variable name="quantity" />
    <variable name="partNum" />
    <variable name="name" />
    <variable name="dueDate" />
    <variable name="billingInfo" />
  </head>

  <results>
    <result>
      <binding name="quantity">
        <literal>12.0</literal>
      </binding>

      <binding name="partNum">
        <literal>052053811</literal>
      </binding>

      <binding name="name">
        <literal>John Smith</literal>
      </binding>

      <binding name="billingInfo">
        <literal>88 Park Road, Lower Dangan, Galway, Ireland</literal>
      </binding>

      <binding name="dueDate">
        <literal>20061114</literal>
      </binding>

    </result>
    </results>
</sparql>

 <xsl:transform version="2.0"
    xmlns:po="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/PurchaseOrderService#"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:sp="http://www.w3.org/2005/sparql-results#">

  <xsl:output method="xml" version="1.0" encoding="iso-8859-1" indent="yes" />
  <xsl:template match="/sp:sparql">
    <po:OrderRequest>
      <xsl:variable name="fullName">
        <xsl:value-of select="sp:results/sp:result[position()=1]/sp:binding[@name='name']/sp:literal"/>
      </xsl:variable>
      <po:firstName>
         <xsl:value-of select="substring-before($fullName,' ')" />
      </po:firstName>
      <po:lastName>
         <xsl:value-of select="substring-after($fullName,' ')" />
      </po:lastName>
      <xsl:apply-templates select="sp:results/sp:result" />
    </po:OrderRequest>
    </xsl:template>
    <xsl:template match="sp:result">
    <po:"item">
      <po:itemCode>
        <xsl:value-of select="sp:binding[@name='partNum']/sp:literal" />
      </po:itemCode>
      <po:quantity>
          <xsl:value-of select="sp:binding[@name='quantity']/sp:literal" />
      </po:quantity>
      <po:dueDate>
        <xsl:value-of select="sp:binding[@name='dueDate']/sp:literal" />
      </po:dueDate>
      <po:billingInfo>
        <xsl:value-of select="sp:binding[@name='billingInfo']/sp:literal" />
      </po:billingInfo>
    </po:item>
  </xsl:template>
</xsl:transform>
</lowering>

<po:OrderRequest
  xmlns:po="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/PurchaseOrderService#"
  xmlns:sp="http://www.w3.org/2005/sparql-results#"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema">

    <po:firstName>John</po:firstName>
    <po:lastName>Smith</po:lastName>
    <po:item>
      <po:itemCode>052053811</po:itemCode>
      <po:quantity>12.0</po:quantity>
      <po:dueDate>20061114</po:dueDate>
      <po:billingInfo>88 Park Road, Lower Dangan, Galway, Ireland</po:billingInfo>
    </po:item>
</po:OrderRequest> 

<wsdl:description>
  ...
  <wsdl:types>
  <xsd:schema
    targetNamespace="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/MyPurchaseOrder#" elementFormDefault="qualified">

    <xsd:element name="MyOrderRequest">
      <xsd:complexType sawsdl:loweringSchemaMapping="http://www.w3.org/2002/ws/sawsdl/spec/examples/mapping/Ont2MyOrderRequest#lowering">
        <xsd:sequence>
          <xsd:element name="firstinitial" type="xsd:string"/>
          <xsd:element name="lastName" type="xsd:string"/>
          <xsd:element name="item" type="item" minOccurs="1" maxOccurs="unbounded" />
        </xsd:sequence>
      </xsd:complexType>
    </xsd:element>

    <xsd:complexType name="item">
      <xsd:all>
        <xsd:element name="itemCode" type="xsd:string"/>
        <xsd:element name="quantity" type="xsd:float"/>
        <xsd:element name="dueDate" type="xsd:string"/>
        <xsd:element name="billingInfo" type="xsd1:POBilling"/>
      </xsd:all>
    </xsd:complexType>

    <xsd:element name="OrderResponse" type="Confirmation"/>
    <xsd:simpleType name="Confirmation">
      <xsd:restriction base="xsd:string">
        <xsd:enumeration value="Confirmed"/>
        <xsd:enumeration value="Pending"/>
        <xsd:enumeration value="Rejected"/>
      </xsd:restriction>
    </xsd:simpleType>
  </xsd:schema>
  </wsdl:types>

  <wsdl:interface name="Order">
    <wsdl:operation name="order" pattern="http://www.w3.org/2006/01/wsdl/in-out">
      <wsdl:input element="MyOrderRequest"/>
      <wsdl:output element="OrderResponse"/>
    </wsdl:operation>
  </wsdl:interface>
</wsdl:description>
  ...

 <xsl:transform version="2.0"
    xmlns:po="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/PurchaseOrderService#"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:sp="http://www.w3.org/2005/sparql-results#">

  <xsl:output method="xml" version="1.0" encoding="iso-8859-1" indent="yes" />
  <xsl:template match="/sp:sparql">
    <po:OrderRequest>
        <xsl:variable name="fullName">
          <xsl:value-of select="sp:results/sp:result[position()=1]/sp:binding[@name='name']/sp:literal"/>
        </xsl:variable>
        <po:firstName>
          <xsl:value-of select="substring(substring-before($fullName,' '),1,1)" />
        </po:firstName>
        <po:lastName>
          <xsl:value-of select="substring-after($fullName,' ')" />
        </po:lastName>
      <xsl:apply-templates select="sp:results/sp:result" />
    </po:OrderRequest>
    </xsl:template>
    <xsl:template match="sp:result">
    <po:item>
      <po:itemCode>
        <xsl:value-of select="sp:binding[@name='partNum']/sp:literal" />
      </po:itemCode>
      <po:quantity>
          <xsl:value-of select="sp:binding[@name='quantity']/sp:literal" />
      </po:quantity>
      <po:dueDate>
        <xsl:value-of select="sp:binding[@name='dueDate']/sp:literal" />
      </po:dueDate>
      <po:billingInfo>
        <xsl:value-of select="sp:binding[@name='billingInfo']/sp:literal" />
      </po:billingInfo>
    </po:item>
  </xsl:template>
</xsl:transform>
</lowering>

<po:OrderRequest
  xmlns:po="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/PurchaseOrderService#"
  xmlns:sp="http://www.w3.org/2005/sparql-results#"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema">

    <po:firstName>J</po:firstName>
    <po:lastName>Smith</po:lastName>

  <po:item>
    <po:itemCode>052053811</po:itemCode>
    <po:quantity>12.0</po:quantity>
    <po:dueDate>20061114</po:dueDate>
    <po:billingInfo>88 Park Road, Lower Dangan, Galway, Ireland</po:billingInfo>
  </po:item>
</po:OrderRequest> 

_:req :hasCustomer
  [ a :Customer;
    :hasCustomerName
      [ a :Name;
        :hasLexicalRespresentation xpath(concat(order:firstName, " ", order:lastName)) ] ] .

<xsd:element name="OrderRequest">
  <xsd:complexType sawsdl:liftingSchemaMapping="http://www.w3.org/2002/ws/sawsdl/spec/examples/mapping/OrderRequest2Ont.xslt"
     sawsdl:liftingSchemaMapping="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/OrderRequest-SPAT.ttl#OReq"
     sawsdl:loweringSchemaMapping="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/OrderRequest-SPAT.ttl#OReq">
    <xsd:sequence>
      <xsd:element name="firstName" type="xsd:integer" />
      <xsd:element name="lastName" type="xsd:integer" />
      <xsd:element name="item" type="item" minOccurs="1" maxOccurs="unbounded" />
    </xsd:sequence>
  </xsd:complexType>
</xsd:element>

<OrderRequest xmlns="http://www.w3.org/2002/ws/sawsdl/spec/examples/wsdl/PurchaseOrderService#">
  <firstName>John</firstName>
  <lastName>Smith</lastName>
  <orderItem quantity="12.0">
    <partNum>052053811</partNum>
    <dueDate>20061114</dueDate>
    <billingInfo>88 Park Road, Lower Dangan, Galway, Ireland</dueDate>
  </orderItem>
</OrderRequest>

@prefix foaf:
<http://xmlns.com/foaf/0.1/> .

[] foaf:givenName "John" ;
   foaf:familyName "Smith" .

<operation name="ItemSearch" pattern="http://www.w3.org/2006/01/wsdl/in-out"
   sawsdl:modelReference="AWSECommerceService-SAWSDL-item-terms#ProductSearch">
  <input element="tns:ItemSearch"/>
  <output element="tns:ItemSearchResponse"/>
</operation>
<operation name="ItemLookup" pattern="http://www.w3.org/2006/01/wsdl/in-out"
   sawsdl:modelReference="AWSECommerceService-SAWSDL-item-terms#ProductDetails">
  <input element="tns:ItemLookup"/>
  <output element="tns:ItemLookupResponse"/>
</operation>

<xsd:complexType name="ItemSearchRequest"
   sawsdl:liftingSchemaMapping="AWSECommerceService-SAWSDL-item-terms.ttl#keywords">
  <xsd:sequence>
    <xsd:element name="Keywords" type="xsd:string" minOccurs="0"/>
    <xsd:element name="SearchIndex" type="xsd:string" minOccurs="0"/>
  </xsd:sequence>
</xsd:complexType>

:keywords spat:SPAT '?req :keywords xpath("tns:Keywords") ; :index    xpath("tns:SearchIndex")' .

@prefix tns: <wsdl/AWSECommerceService-SAWSDL-item-terms.ttl#> .
[] tns:id "0FWYBWB91M5S26YBE382" ;
   tns:keywords "Weaving" ;
   tns:index "Books" .

<?xml version="1.0" encoding="UTF-8"?>
  ...<SOAP-ENV:Body>
  <ItemSearch xmlns="">
    <SubscriptionId xsi:type="xsd:string">0FWYBWB91M5S26YBE382</SubscriptionId>
    <Request>
      <Keywords xsi:type="xsd:string">Weaving</Keywords>
      <SearchIndex xsi:type="xsd:string">Books</SearchIndex>
    </Request>
  </ItemSearch>
  </SOAP-ENV:Body>...

<xsd:element name="Item">
  <xsd:complexType>
    <xsd:sequence sawsdl:loweringSchemaMapping="AWSECommerceService-SAWSDL-item-terms.ttl#asin">
      <xsd:element name="ASIN" type="xsd:string"/>...
      <xsd:element ref="tns:ItemAttributes" minOccurs="0"/>
    </xsd:sequence>
  </xsd:complexType>
</xsd:element>
<xsd:element name="ItemAttributes">
  <xsd:complexType sawsdl:loweringSchemaMapping="AWSECommerceService-SAWSDL-item-terms.ttl#title">
    <xsd:sequence>...
      <xsd:element name="Title" type="xsd:string" minOccurs="0"/>
    </xsd:sequence>
  </xsd:complexType>
</xsd:element>

...
     <Item>
       <ASIN>1883010039</ASIN>
       <ItemAttributes>
         ...
         <Title>Learning to Weave, Revised Edition</Title>
       </ItemAttributes>
     </Item>...

...
[] :asin "1883010039" ;
   :title "Learning to Weave, Revised Edition" .