Section 6.2. History

6.2. History

WSDL was created in one month in September 2000 by combining two service description languages: NASSL (Network Application Service Specification Language) from IBM and SDL (Service Description Language) from Microsoft. NASSL had a structure similar to WSDL in terms of an abstract part that was bound to specific concrete wire protocols and formats. However, NASSL was heavily focused on describing remote procedure call (RPC)style interactions rather than message-oriented interactions. NASSL was focused on enabling not only XML-based interaction with a service, but also other formats and protocols, such as IIOP and in-memory method calls. NASSL did not constrain itself to what most people consider the Web, which is the graph of servers that support the HTTP protocol; rather, it wanted to support any network connected, accessible service.

SDL, on the other hand, had almost the opposite structure. A service that was offered over multiple protocols was described as if each was a completely different service, without a common underlying abstract service description. It was, however, much more message-centric than NASSL.

The combined language WSDL was designed to marry RPC and messaging while supporting multiple protocols and message formats. Details of WSDL and how that was achieved are discussed later in this chapter.

Since the release of WSDL 1.0 in September 2000, a slightly updated version, 1.1, was released later that year and submitted to the W3C for standardization in 2001. WSDL 1.1 is now widely used and is a de facto standard for describing Web services. The Web Service Description Working Group of the W3C is almost finished with a new version of WSDL. It will be called WSDL 2.0 to reflect the significant changes and improvements that have been incorporated to it.