[Appendix A] : Critique of WSDL as a Language Definition

The WSDL format for describing services is based on a notion of simple services. A simple service takes one request (data), transforms it in some (useful) way, and returns one output (data) - or a statement of error, is otherwise stateless, and has no public side effects.
SimpServ ={ Input <data>, Output <data>}

• A simple service is a WSDL Operation.
  A WSDL Service is a set of
  Ports, which are sets of bindings to
  PortTypes, which are sets of operations.
• Operations have input and output messages
  The messages may have various parts,
  which may be AND/OR (using the <choice> tag.)
• Usually the messages are one-way or simple request-response received then sent by the service.
• However, in theory, the services may also initiate messages:
  solicit-response and notification messages are important for extended transaction services.
• The two response type of messages support an optional fault tag as well as input and output tags.

The primary deficiencies of this format as a language are:

• There are no input or output parameters, like all other reasonable languages,
• There is no reference by pointer (only value except perhaps a URL could be used),
• A service is called an "operation" and a "service" is really a collection of entrypoints, for a service provider, that might have better been called a "service package" or "service platform".
• The tag system is hierarchical rather than relational and sometimes the hierarchical means association and sometimes aggregation, and is inconsistent.
  • Service aggregates Ports
  • Binding is a part of the Port tag as well as its own tag,
    which associates a Port with a PortType.
  • PortType aggregates Operations
  • Operations are a supertag for the input and "output" tags
    of which Message is a part.
  • Message tags are not defined as subtags of Operations but as stand-alone tags associated, like the Binding tag.
• The "standard" has no certification as evidenced by typos in the very first example¹ in the W3C document.
  • binding="tns:StockQuoteBinding"
  • binding name="StockQuoteSoapBinding"

1 http://www.w3.org/TR/wsdl#_wsdl