John McDowall argues that there is no need to agree on just one service description language.

I believe that it’s probably best to have none at all [1].

Interfaces are a great way to introduce boundaries in closed, tightly coupled software systems; depending on the interface enables you to plug in implementations as you need them. But in the Web services world, it’s an unattainable pipe dream that you will ever be able to design the perfect interface. Designing interfaces correctly requires that you know up front how and — at least to a certain degree — by whom your services will be used. Whatever way you choose to decide whether a bunch of operations belong to a single interface, or two, or more, you’ll end up with a use case later that will demonstrate that you made the wrong decision.

[1] Of course a single, uniform one will do as well.