TheArchitect.co.uk - Jorgen Thelin's weblog

Modelling without WSDL

In Mark Ericson's blog he raises some interesting questions about interface design:

As I was creating a new Web Service last night I kept asking myself, "what is bothering me about WSDL?" It finally occurred to me, WSDL is too cumbersome for rapid modeling of service interfaces. I would like a "language" that allows me to model an interface without concern of programming language or deployment.

It seems to me there are three distinct start points emerging from which to create a web services interface :

• a payload defininition written in XML Schema, to which a WSDL wrapper is applied
• a list of rpc-style method defininitions written in a programming language such as Java
• a list of rpc-style method / operation defininitions written in a language-neutral design description language such as UML

I don't know whether starting from UML fulfils Mark's requirements for the ideal interface design language, but I can see many people will want to use this approach in the near future. Certainly all the theory says that UML should provide exactly such an abstract modeling mechanism

I do share Mark's concerns about the approach of starting from a specific programming language:

there always seems to be some loss of fidelity, or language-specific features that "show-through" in that conversion process

There still seems to be two distinct views of the world here - some people want to start with the payload and work "outwards", while some people want to start with the operation and work "inwards". It is hard to describe either group as more-right or more-wrong than the other, and I think it is the duty of web services tools vendors to accomodate both or risk losing half their target market.