At the abstract level, the Definitions component is just a container for two categories of components; WSDL components and type system components.

WSDL components are interfaces, bindings and services.

Type system components are element declarations drawn from some type system. They define the [local name], [namespace name], [children] and [attributes] properties of an element information item.

The properties of the Definitions component are as follows:

The set of interfaces/binding/services/etc. available in the Definitions component include those that are defined within the component itself and those that are imported and/or included. Note that at the component model level, there is no distinction between directly defined components vs. imported/included components.

The components directly defined within a single Definitions component are said to belong to the same target namespace. The target namespace therefore groups a set of related component definitions and represents an unambiguous name for the intended semantics of the components. The target namespace URI SHOULD point to a human or machine processable document that directly or indirectly defines the intended semantics of those components.

Note that it is RECOMMENDED that the value of the targetNamespace attribute information item SHOULD be a dereferencible URI and that it resolve to a WSDL document which provides service description information for that namespace.

If a service description is split into multiple documents (which may be combined as needed via ), then the targetNamespace attribute information item SHOULD resolve to a master document which includes all the WSDL documents needed for that service description. This approach enables the WSDL component designators' fragment identifiers to be properly resolvable.

Imported components have different target namespace values from the Definitions component that is importing them. Thus importing is the mechanism to use components from one namespace in another set of definitions.

Each WSDL or type system component MUST be uniquely identified by its qualified name. That is, if two distinct components of the same kind (Interface, Binding etc.) are in the same target namespace, then their QNames MUST be unique. However, different kinds of components (e.g., an Interface component and a Binding component) MAY have the same QName. Thus, QNames of components must be unique within the space of those components in a given target namespace.

In addition to WSDL components and type system components, additional extension components MAY be added via extensibility . Further, additional properties to WSDL and type system components MAY also be added via extensibility.

WSDL definitions are represented in XML by one or more WSDL Information Sets (Infosets), that is one or more definitions element information items. A WSDL Infoset contains representations for a collection of WSDL components which share a common target namespace. A WSDL Infoset which contains one or more import element information items corresponds to a collection with components drawn from multiple target namespaces.

The targetNamespace URI MUST be an absolute URI (see ).

The definitions element information item has the following Infoset properties:

The mapping between the properties of the Definitions component (see ) and the XML Representation of the definitions element information item (see ) is described in .

An Interface component describes sequences of messages that a service sends and/or receives. It does this by grouping related messages into operations. An operation is a sequence of input and output messages, an interface is a set of operations.

An interface can optionally extend one or more other interfaces. In such cases the interface contains the operations of the interfaces it extends, along with any operations it defines. The interfaces a given interface extends MUST NOT themselves extend that interface either directly or indirectly.

Interfaces are named constructs and can be referred to by QName (see ). For instance, Binding components refer to interfaces in this way.

The properties of the Interface component are as follows:

For each Interface component in the {interfaces} property of a definitions container, the combination of {name} and {target namespace} properties MUST be unique.

The XML representation for an Interface component is an element information item with the following Infoset properties:

The mapping between the properties of the Interface component (see ) and the XML Representation of the interface element information item (see ) is as described in .

Note that, per , the Interface components in the {extended interfaces} property of a given Interface component MUST NOT contain that Interface component in any of their {extended interfaces} properties, that is to say, recursive extension of interfaces is disallowed.

An Interface Fault component describes a fault that MAY be occur during execution of an operation of the interface. The Interface Fault component declares a fault by naming it and indicating the content or payload of the fault message. When and how the fault message flows is indicated by the Interface Operation component .

The reason the Interface Fault component is a property of the Interface component is because that provides a convenient mechanism to declare a set of fault message types and then indicate which operations use those types, thus allowing one to easily indicate that the same fault message type can occur in multiple operations.

The properties of the Interface Fault component are as follows:

If a non-XML type system is in use (as considered in ) then additional properties would need to be added to the Fault Component (along with extensibility attributes to its XML representation) to allow associating such message types with the message reference.

For each Interface Fault component in the {faults} property of an Interface component, the combination of {name} and {target namespace} properties must be unique.

Interface Fault components are local to Interface components; they cannot be referred to by QName, despite having both {name} and {target namespace} properties. That is, two Interface components sharing the same {target namespace} property but with different {name} properties MAY contain Interface Fault components which share the same {name} property. Thus, the {name} and {target namespace} properties of the Interface Fault components are not sufficient to form the unique identity of an Interface Fault component. To uniquely identify an Interface Fault component one must first identify the Interface component (by QName) and then identify the Interface Fault within that Interface component (by a further QName).

In cases where, due to an interface extending one or more other interfaces, two or more Interface Faults components have the same value for their {name} and {target namespace} properties, then the component models of those Interface Fault components MUST be equivalent (see ). If the Interface Fault components are equivalent then they are considered to collapse into a single component. It is an error if two Interface Fault components have the same value for their {name} and {target namespace} properties but are not equivalent.

Note that, due to the above rules, if two interfaces that have the same value for their {target namespace} property also have one or more faults that have the same value for their {name} property then those two interfaces cannot both form part of the derivation chain of a derived interface unless those faults are the same fault.

The XML representation for an Interface Fault component is an element information item with the following Infoset properties:

The mapping between the properties of the Interface Fault component (see ) and the XML Representation of the fault element information item (see ) is as described in .

An Interface Operation component describes an operation that a given interface supports. An operation is an interaction with the service consisting of a set (ordinary and fault) messages exchanged between the service and the other roles involved in the interaction, in particular the service requestor. The sequencing and cardinality of the messages involved in a particular interaction is governed by the message exchange pattern used by the operation (see {message exchange pattern} property).

A message exchange pattern defines placeholders for messages, the participants in the pattern (i.e., the sources and sinks of the messages), and the cardinality and sequencing of messages exchanged by the participants. The message placeholders are associated with specific message types by the operation that uses the pattern by means of message and fault references (see {message references} and {fault references} properties). The service whose operation is using the pattern becomes one of the participants of the pattern. This specification does not define a machine understandable language for defining message exchange patterns, nor does it define any specific patterns. The companion specification, defines a set of such patterns and defines identifying URIs any of which MAY be used as the value of the {message exchange pattern} property.

The properties of the Interface Operation component are as follows:

For each Interface Operation component in the {operations} property of an Interface component, the combination of {name} and {target namespace} properties MUST be unique.

Interface Operation components are local to Interface components; they cannot be referred to by QName, despite having both {name} and {target namespace} properties. That is, two Interface components sharing the same {target namespace} property but with different {name} properties MAY contain Interface Operation components which share the same {name} property. Thus, the {name} and {target namespace} properties of the Interface Operation components are not sufficient to uniquely identify an Interface Operation component. In order to uniquely identify an Interface Operation component, one must first identify the Interface component (by QName) and then identify the Interface Operation within that Interface component (by a further QName).

In cases where, due to an interface extending one or more other interfaces, two or more Interface Operation components have the same value for their {name} and {target namespace} properties, then the component models of those Interface Operation components MUST be equivalent (see ). If the Interface Operation components are equivalent then they are considered to collapse into a single component. It is an error if two Interface Operation components have the same value for their {name} and {target namespace} properties but are not equivalent.

Note that, due to the above rules, if two interfaces that have the same value for their {target namespace} property also have one or more operations that have the same value for their {name} property then those two interfaces cannot both form part of the derivation chain of a derived interface unless those operations are the same operation.

The XML representation for an Interface Operation component is an element information item with the following Infoset properties:

The mapping between the properties of the Interface Operation component (see ) and the XML Representation of the operation element information item (see ) is as described in .

The RPC style is selected by assigning to an Interface Operation component's {style} property the value http://www.w3.org/2004/03/wsdl/style/rpc.

The RPC style MUST NOT be used for Interface Operation components whose {message exchange pattern} property has a value other than 'http://www.w3.org/2004/03/wsdl/in-only' or 'http://www.w3.org/2004/03/wsdl/in-out'.

Use of this value indicates that XML Schema was used to define the schemas of the {element} properties of all {message reference} components of the Interface Operation component. Those schemas MUST adhere to the rules below.

Note that if the Interface Operation component uses the {message exchange pattern} 'http://www.w3.org/2004/03/wsdl/in-only' then there is no output element and hence the rules which refer to the output element do not apply.

A Message Reference component associates to a message exchanged in an operation an XML element declaration that specifies its message content.

Message Reference components are identified by the role the message plays in the {message exchange pattern} that the operation is using. That is, a message exchange pattern defines a set /meof placeholder messages that participate in the pattern and assigns them unique names within the pattern. The purpose of a Message Reference component is to associate an actual message type (XML element declaration or some other declaration (see ) for message content) with the message that will perform a specific role in the message exchange pattern.

The properties of the Message Reference component are as follows:

If a non-XML type system is in use (as considered in ) then additional properties would need to be added to the Message Reference Component (along with extensibility attributes to its XML representation) to allow associating such message types with the message reference.

For each Message Reference component in the {message references} property of an Interface Operation component, its {message label} property MUST be unique.

The XML representation for a Message Reference component is an element information item with the following Infoset properties:

The mapping between the properties of the Message Reference component (see ) and the XML Representation of the message reference element information item (see ) is as described in .

A Fault Reference component associates a Fault component that defines the fault message type for a fault that occurs related to a message participating in an operation.

Fault Reference components are identified by the role the related message plays in the {message exchange pattern} that the operation is using. That is, a message exchange pattern defines a set of placeholder messages that participate in the pattern and assigns them unique labels within the pattern. The purpose of a Fault Reference component is to associate an actual Fault component for the fault that will occur with a specific message in the message exchange pattern.

The companion specification defines two fault patterns that a given message exchange pattern may use. For the pattern fault-replaces-message, the message that the fault relates to identifies the message in place of which the declared fault message will occur. Thus, the fault message will travel in the same direction as the message it replaces in the pattern. For the pattern message-triggers-fault, the message that the fault relates to identifies the message after which the indicated fault may occur, in the opposite direction of the referred to message. That is, the fault message will travel in the opposite direction of the message it comes after in the pattern.

More than one Fault Reference component may refer to the same message label. This allows one to indicate that there is more than one type of fault that is related to that message.

The properties of the Fault Reference component are as follows:

The XML representation for a Fault Reference component is an element information item with the following Infoset properties:

The mapping between the properties of the Fault Reference component (see ) and the XML Representation of the message reference element information item (see ) is as described in .

A feature component describes an abstract piece of functionality typically associated with the exchange of messages between communicating parties. Although WSDL poses no constraints on the potential scope of such features, examples might include "reliability", "security", "correlation", and "routing". The presence of a feature component in a WSDL description indicates that the service supports the feature and may require a requester agent that interacts with the service to use that feature. Each Feature is identified by its URI.

The properties of the Feature component are as follows:

The XML representation for a Feature component is an element information item with the following Infoset properties:

The mapping between the properties of the Feature component (see ) and the XML Representation of the feature element information item (see ) is as described in .

A Property component describes the set of possible values for a particular property. The permissible values are specified by references to a Schema description. A property is typically used to control a feature's behavior. Properties, and hence property values, can be shared amongst features.

The properties of the Property component are as follows:

The XML representation for a Property component is an element information item with the following Infoset properties:

The mapping between the properties of the Property component (see ) and the XML Representation of the property element information item (see ) is as described in .

A Binding component describes a concrete message format and transmission protocol which may be used to define an endpoint (see ). Binding components can be used to describe such information in a re-usable manner for any interface or specifically for a given interface. Furthermore, binding information MAY be specified on a per-operation basis (see ) within an interface in addition to across all operations of an interface.

If a Binding component specifies any operation-specific binding details (by including Binding Operation components) or any fault binding details (by including Binding Fault components) then it MUST specify an interface the Binding component applies to, so as to indicate which interface the operations come from.

Conversely, a Binding component which omits any operation-specific binding details and any fault binding details MAY omit specifying an interface. Binding components that do not specify an interface MAY be used to specify operation-independent binding details for Service components with different interfaces. That is, such Binding components are reusable across one or more interfaces.

No concrete binding details are given in this specification. The companion specification, WSDL (Version 2.0): Bindings defines such bindings for SOAP 1.2 and HTTP . Other specifications MAY define additional binding details. Such specifications are expected to annotate the Binding component (and its sub-components) with additional properties and specify the mapping between those properties and the XML representation.

A Binding component which defines bindings for an Interface component MUST define bindings for all the operations of that Interface component. The bindings may occur via defaulting rules which allow one to specify default bindings for all operations (see, for example ) or by directly listing each Operation component of the Interface component and defining bindings for them. Thus, it is an error for a Binding component to not define bindings for all the Operation components of the Interface component for which the Binding component purportedly defines bindings for.

Bindings are named constructs and can be referred to by QName (see ). For instance, Endpoint components refer to bindings in this way.

The properties of the Binding component are as follows:

For each Binding component in the {bindings} property of a definitions container, the combination of {name} and {target namespace} properties must be unique.

The XML representation for a Binding component is an element information item with the following Infoset properties:

The mapping between the properties of the Binding component (see ) and the XML Representation of the binding element information item (see ) is as described in .

A Binding Fault component describes a concrete binding of a particular fault within an interface to a particular concrete message format. A particular fault of an interface is uniquely identified by the target namespace of the interface and the name of the fault within that interface.

Note that the fault does not occur by itself - it occurs as part of a message exchange as defined by an Interface Operation component (and its binding counterpart the Binding Operation component). Thus, the fault binding information specified in a Binding Fault component describes how faults that occur within a message exchange of an operation will be formatted.

The properties of the Binding Fault component are as follows:

For each Binding Fault component in the {faults} property of a Binding component, the {fault reference} property MUST be unique. That is, one cannot define multiple bindings for the same fault within a given Binding component.

The XML representation for a Binding Fault component is an element information item with the following Infoset properties: