Web Services Inspection Language (WSIL)

Web Services Inspection Language (WSIL) is a service discovery mechanism that is an alternative to UDDI as well as complementary to UDDI. When you discover Web services with UDDI, you go to a centralized registry.  WSIL is an alternative approach to Web service discovery.  WSIL allows you to go directly to the service provider and ask for the services it provides.

IBM^® and Microsoft's proposal for the WSIL specification is designed around an XML-based model for building an aggregation of references to existing Web service descriptions, that are exposed using standard Web server technology.

WSIL provides a distributed service discovery method that supplies references to service descriptions at the service provider's point-of-offering, by specifying how to inspect a Web site for available Web services. The WSIL specification defines the locations on a Web site where you can look for Web service descriptions.

Since WSIL focuses on distributed service discovery, the WSIL specification complements UDDI by facilitating the discovery of services that are available on Web sites that may not be listed yet in a UDDI registry. A separate topic in this documentation discusses the Relationship between UDDI and WSIL.

The WSIL specification does not define a service description language.  WSIL documents provide a method for aggregating different types of service descriptions.  Within a WSIL document, a single service can have more than one reference to a service description.  For example, a single Web service might be referenced twice in a WSIL document: once directly via its WSDL, and again via its businessService entry in a UDDI registry. References to these two service descriptions should be put into a WSIL document.  If multiple references are available, it is beneficial to put all of them in the WSIL document so that the application that uses the document can select the type of service description that is compatible with and preferred by that application.

The WSIL specification serves two primary functions:

• WSIL defines an XML format for listing references to existing service descriptions. These service descriptions can be defined in any format, such as WSDL, UDDI, or plain HTML.  A WSIL document is generally made available at the point-of-offering for the services that are referenced within the document. A WSIL document can contain a list of references to service descriptions, as well as references to other WSIL documents.

  The ability to link a WSIL document to one or more different WSIL documents allows you to manage service description references by grouping them into different documents and to build a hierarchy of WSIL documents.  For example, separate WSIL documents can be created for different categories of services, and one primary WSIL document can link all of them together.

• WSIL defines a set of conventions so that it is easy to locate other WSIL documents. The WSIL specification does not limit the type of service descriptions that can be referenced.  The WSIL specification defines a set of standard extensibility elements for both WSDL and UDDI.  The WSIL specification is the definition of locations where you can access WSIL documents.
• Two conventions make the location and retrieval of WSIL documents easy:
  • Fixed-name WSIL documents. The fixed name for WSIL documents is inspection.wsil.  The inspection.wsil file is placed at common entry points for a Web site.  For example, if the common entry point is http://entrypoint.com then the location of the WSIL document would be http://entrypoint.com/inspection.wsil
  • Linked WSIL documents. References to WSIL documents can also appear within different content documents, such as HTML pages.

For more information on the Web Services Inspection Language specification, refer to www.ibm.com/developerworks/webservices/library/ws-wsilspec.html

• Relationship between UDDI and WSIL
  The Web Services Inspection Language (WSIL) and the Universal Description, Discovery, and Integration (UDDI) specification both address issues related to Web service discovery. However, each specification takes a different approach to the discovery of Web services. The two specifications can be used separately or jointly; searching with WSIL can result in finding items in UDDI.