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Is WS-MetadataExchange Really Necessary?
I’ll admit it: I don’t really get WS-MetadataExchange (or WS-MEX, as it’s affectionately known). I understand why someone might want to get the Schema, WSDL, and WS-Policy data for a service. I’m just not clear on why a simple URL isn’t good enough. Why do we need to invent new RPC-style request/response pairs?
I guess I can see that this allows me to have one URL for the service that can be interrogated for all three in a standard way. Otherwise, I have to tell you three URLs to give you the metadata instead of one, but couldn’t we just as easily agree to some kind of convention like this:
http://www.example.com/service_path?meta=wsdl http://www.example.com/service_path?meta=schema http://www.example.com/service_path?meta=policy
This seems much simpler and easier to implement than a request response pair. Plus, I can still grab each of these important documents in a browser and inspect them when I want without having to have a special tool. Am I missing something?
Posted by windley on April 28, 2005 10:35 AM
Comment from Michael at April 28, 2005 6:58 PM
I agree with you. This is just another standard to be ignored.
There is really no benefit to this that I can see... discovering what the WSDL is, and how to map it to my application is very much a human activity, so why have a WS- standard for retrieving it?
What is annoying about this is that it distracts people (and implementers) from the WS-* standards that actually do matter, and are needed (like security, transactions, asynchronous etc).
Alot of these standards still aren't well supported by tools, and adding more will just make things worse.
Comment from Todd Biske at April 28, 2005 8:10 PM
Phil-
I've posted an answer to your question on my blog. Give it a read and let me know if you agree or disagree.
Comment from Sean at April 28, 2005 10:37 PM
MSFT is totally enamored with WS-Soup. It's so over the top that all you can do is laugh.
Comment from Michael at April 29, 2005 3:03 AM
Todd, I understand your comments the WS-Mex will be necessary to support the "important" WS standards.
However, I think the "breaking the code/build.." thing can sometimes be oversold. For instance, changing transaction or security behaviour is not an idle decision to make. In reality, there would be a lot of work behind the scenes should one chose to change security or transactional or sychronous nature of the use of a service.
If WS-Mex is genuinely needed to support these other interesting standards, great. But it does kind of sound like overengineering ... and you can excuse people for being cynical, given the lack of update of WS-* standards (which is a shame).
I am forever explaining to people what we can't do "yet" with WS, which is always a step back from things like MQ/Message based middleware. And always saying, "but soon the tool support for standard WS...." etc...
been a bad week.
Comment from Todd Biske at April 29, 2005 7:28 PM
It's not solely about changes to policy. I actually think the biggest reason that we need it is that non-functional requirements like encryption and security aren't in the WSDL file. This is the right decision, however, because there are different people responsible for these policies, at least at my organization. The developer can masintain the WSDL, while compliance or securitty can maintain the other policies exchanged through WS-Mex. It's all moot until there's some decent support. WS-Policy seems to be gaining some momentum, although it's still too tightly coupled to policy enforcement devices.
Comment from Phil Windley at April 29, 2005 9:25 PM
Todd and Michael, your comments seem to be more about the need for WS-Policy, which I'm not disputing. In fact, I think we'll see more meta data about Web services as time goes on, not less.
By beef is with WS-Mex. That one seems like it could be handled with URLs much more easily.
Comment from Stefan Tilkov at April 29, 2005 11:57 PM
See my take on this here: http://www.innoq.com/blog/st/2005/04/28/reinvent.html
Comment from David Totzke at May 2, 2005 10:34 AM
Don Box explains why they did what they did over on his blog:
http://pluralsight.com/blogs/dbox/archive/2005/04/30/7885.aspx