RE: Is This a Web Service?

David,
 
Yes, I should have been more clear.  I was assuming a kind of two step definition, in keeping with the approach to architecture in general.  The definition needs to be technology neutral to the extent possible, then specific examples cited that fit the definition.
 
So I would agree with you, first define the what, as I proposed, and then say something like "for example, Web services are implemented using SOAP, WSDL, and UDDI."
 
Eric

-----Original Message-----
From: Burdett, David [mailto:david.burdett@commerceone.com]
Sent: Tuesday, April 15, 2003 3:27 PM
To: Newcomer, Eric; Walden Mathews; Champion, Mike; Www-Ws-Arch@W3. Org
Subject: RE: Is This a Web Service?


Eric
 
In many ways I like your definition except that it does not mention ANY of the well known "web services standards" such as SOAP, WSDL and UDDI. This makes me think that perhaps there are two steps to defining a web serivice ...
 
1. Define a web service in a standards neutral way - along the lines of your definition or some variant. This defines WHAT a web service is
2. Define sets of standards that can implement a Web Service. This defines HOW you implement a web service
 
Drawing an analogy to creating a building, the first is like the architects drawing of the end result. The second is the result of the architect and the quantity survey coming up with detailed plans of how the building will be built. They are both valid "architectural" activities.
 
I also think that agreeing on the first step might make it easier to come up with the second. However it also raises the issue of how you use standards together which WS-I is doing, should this be our perogative?
 
David

-----Original Message-----
From: Newcomer, Eric [mailto:Eric.Newcomer@iona.com]
Sent: Tuesday, April 15, 2003 11:03 AM
To: Walden Mathews; Champion, Mike; Www-Ws-Arch@W3. Org
Subject: 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.