RE: Is This a Web Service?

Hi,
 
I'd like to propose a definition I worked up recently:
 
"A Web service is an XML interface to an executable software agent that is accessible using Web technologies.  A Web service has a description, identified and published using a URI.  The agent has a network address, also identified and published using a URI.  A Web service description defines the set of one or more XML messages that can be sent to and/or received from a Web service.   A Web service description may be discovered using a registry, directory, or other mechanism that associates human readable keywords with descriptions."
 
In particular, I've been trying to establish the separation between the applications of XML that Web services consist of (i.e. the set of schemas, DTDs, etc.) and the executable environments onto which they are mapped or transformed.  For one thing, Web services specifications define XML "representations" of things and while they often include processing model information, the artifacts are nonetheless distinct.  The same Web service can be executed in disparate software environments, meaning the "XML layer" needs to be distinct from the software agents that execute the services.  
 
So I think it's really important to include in the definition at least this distinction.  For example, to clarify the fact that the Web services description or interface is a separate Web resource.  It could live at the same URI as the executable agent, and many implementations do in fact work this way (dereferencing the URI gets you the WSDL file that describes the executable service accessible at the same endpoint address).  
 
I think the fact that a description also is discoverable is part of the definition of a Web service.
 
Eric 
 
 

-----Original Message-----
From: Walden Mathews [mailto:waldenm@optonline.net]
Sent: Tuesday, April 15, 2003 1:45 PM
To: Champion, Mike; Www-Ws-Arch@W3. Org
Subject: Re: Is This a Web Service?


Mike,
 
I disagree about the "how to construct the URL" part -- that's brittle at best.  The
handling of forms should be considered in the set of "generic web protocols".   And I'm
not clear on your requirements about the format.  Are you saying that if the service
just says "responses are in XHTML" that would be good enough?
 
Anyway, Anne's proposal was only a SHOULD w.r.t. interface description at that
level, and so if that's valid, then going without should also work.  Just testing the
[pond] waters...
 
Walden
 
 
----- Original Message ----- 

From: Champion, Mike <mailto:Mike.Champion@SoftwareAG-USA.com>  
To: Www-Ws-Arch@W3. Org 
Sent: Tuesday, April 15, 2003 1:25 PM
Subject: RE: Is This a Web Service?

 

-----Original Message-----
From: Walden Mathews [mailto:waldenm@optonline.net]
Sent: Tuesday, April 15, 2003 1:16 PM
To: Anne Thomas Manes; Www-Ws-Arch@W3. Org
Subject: Re: Is This a Web Service?


 
How about leaving off the "should" on the first one, or amending that sentence to read "The service
should provide some type of description of its interface, or restrict itself to a generic web interface." 
 

I have a hard time with this.  "Generic web interface" in the REST sense says nothing about the rules for generating the URI or the format of the data to be retrieved.
 
Think of Google (the "classic" HTTP/HTML version) ... it might be thought of as a Web service *if* they described the rules for generating a query (apparently pretty simple, just concatenate the search terms together with a "+"), and if they described the format (XHTML  is OK) of the result.  But it's not a "Web service" just by virtue of having a "generic web interface" -- people can use the HTML form on www.google.com and make sense of the result, but machines can't.