WSDL 1.2

The first working draft of WSDL 1.2 specifications has been released. The following discussion pertains to the contents of the first draft of the specification. Some of this information may not be applicable to the final 1.2 specifications. This section summarizes some of the changes between the two versions.

WSDL 1.2 is described using XML information sets. An information set (infoset) is an abstract XML data set. Its primary purpose is to provide a consistent way to describe specifications that describe information in a well-formed XML document structure. As a WSDL document is a well-formed XML document, it can be described as an information set (a tree) with information items (nodes).

The WSDL 1.2 specification introduces a clearer conceptual model for a WSDL document structure. Conceptually, a WSDL document is a container for a WSDL definitions group, which in turn is a container for description components, with each description component describing different parts of the Web service. For example, a message description component describes the abstract messages exchanged by the service and the portType description component describes the abstract service interface. Like WSDL 1.1, WSDL 1.2 describes Web services by defining abstract types, messages, and operations and combining operations into portTypes. However, in WSDL 1.2, a collection of portTypes is defined and called a serviceType, and a service is considered an implementation of a serviceType.

The model dictates six description components, which together provide a complete functional and location description of the service:

• Zero or one type description component

• Zero or more message description components

• Zero or more portType description components

• Zero or more serviceType description components

• Zero or more binding description components

• Zero or more service description components

WSDL 1.2 also attempts to clarify some areas of WSDL 1.1 that were not defined adequately and areas where some WSDL 1.1 service descriptions features could not be supported by all service implementation platforms. For example,

• Although WSDL 1.1 provided for solicit-response and notification type operations, there was no consensus on how these operation types were to be implemented (as callbacks? As event-based notifications?) Also, it is proposed that WSDL 1.2 define an extensible message exchange pattern (MEP), which is in line with the MEP framework defined to work with SOAP 1.2. The MEP framework for SOAP 1.2 is a means to describe a pattern of message exchanges between two SOAP nodes.

• Dropping the support for operator overloading, which was supported in WSDL 1.1 (by providing messages with the same name but different message parts) has also been proposed.

• Moving the parameter order attribute to the binding section. Because parameter order matters only to RPC style invocations, its current placement in the abstract operations description section is incorrect.

Many proposed changes to WSDL stem from the WSDL 1.2 specification's aim of supporting SOAP 1.2. Most of the proposed changes therefore deal with SOAP binding. As SOAP 1.2 specification is in draft form, the proposed changes are not discussed in this section.

To summarize, the main changes to WSDL are to describe the specification itself in a standard manner using information sets, to clarify some of the language descriptions, to remove ambiguities, and to support SOAP 1.2.