web services - Is it mandatory to have a WSDL definition accessible using ?wsdl?

Question

Is it mandated by any standard that a web service should provide a WSDL by appending ?wsdl to the endpoint address?

Is it OK if the WSDL is hosted at a different URL (without appending ?wsdl)?

For example:

Endpoint: http://abc.xyz.com/MyService
WSDL:     http://abc.xyz.com/MyServiceDefinition.pqr

Note that I'm even using a different extension for the WSDL definition.

Does using this approach violate any standards or one can host the thing the way they want?

Answer 1

Is it mandatory to have a WSDL definition accessible using ?wsdl?

No, it's not.

A WSDL is used to describe a web service contract and is provided because it allows tools to automate generation of client stub code for calling the specified web service. Exposing the WSDL at the same location as the web service with ?wsdl appended to it is just very handy and that's the convention everybody uses.

People and tools look for the WSDL at that location and frameworks automatically expose it at that location but it's just a convention. As to my knowledge this isn't specified in any specification (or at least none that I could find).

Sometimes though you don't want to provide a WSDL that everybody can look at and try to create a client because it's a private web service and you only want to give access to your partners, not to everybody. At that point you can disallow the ?wsdl URL and provide the WSDL only to your partners by using an alternative channel. You can even e-mail it if you don't want it exposed online.

So you can choose whatever channel to expose it. Just remember that because people and tools are following this convention they are used to see it there and some (poorly written) tools might choke in a different extension, for example.

P.S. One other thing I wanted to mention - which isn't strictly related to this answer but kinda reinforces the convention - is the new ?singleWsdl option in WCF 4.5.

WCF, as most other tools, exposes the WSDL at the ?wsdl address but uses xsd:import statements with external schemas. Some frameworks were not able to process WSDL with imported dependencies so people started to write customizations over WCF to have a flat WSDL exposed, so much so that in the latest version of WCF Microsoft decided to add this feature out of the box.

But for backward compatibility they needed to keep the ?wsdl endpoint as it was (returning a WSDL document with xsd:import statements inside) and were forced to add a new query parameter for the flat WSDL: ?singleWsdl. I'm sure this idea will be picked up by other web service vendors and providers as well.