Re: Semantics of WSDL vs. semantics of service

This discussion is also giving me an inclination towards preemptive  
deletion of sws-id emails, which is unfortunate. Between the  
confusion of terms (as pointed out, using composition for binding)  
and "descent" to XML Schema arguments, it can't be said to advance  
the cause.

It is rather amazing (heartening or disheartening, I'm not sure) to  
see arguments rehashed which have been going on in the OGC (Open  
Geospatial Consortium) for years. For example, the use of private XML  
message schemas versus SOAP formulations, whether URLencoded service  
invocations using HTTP GET are still important, equating SOAP/WSDL  
with RPC and in turn with the full spectrum of Web service  
possibilities, the idea that the useful information abstractions of  
WSDL should command  slavish devotion to its syntax (as well as claim  
to completeness).

In truth, and disjoint vocabulary aside, we are all fairly well  
agreed on the general information which is needed to productively  
discover, bind, and consume a remote service over the Web. We should  
focus on  the substantive general questions that remain. For  
instance, is it advisable to abstract away all knowledge that an  
operation is being invoked on a remote service over the Web (probably  
not)? Should services be self-describing (probably so)? Is coupled  
content an important part of service semantics (yes and yes)? Does  
WSDL impart all the information needed (for a machine) to use a  
remote service outside of a small circle of friends (no). Is it  
important to represent in service information how a service processes  
inputs to generate outputs (yes, different geocoding services for  
example have their own idiosyncratic heuristics irrespective of the  
syntax)? Where are syntax standards useful for interoperability?  
Should we get all wound up about whether this additional service  
information is contained in a WSDL <definitions> element, referenced  
from within a WSDL <definitions>, outside of a WSDL <definitions>   
(not really that important a question)?

Cheers,

Josh

Joshua Lieberman, Ph.D.
Principal, Traverse Technologies Inc.
mailto:jlieberman@traversetechnologies.com
tel +1 (617) 395-7766
fax +1 (775) 514-6621

On Mar 16, 2006, at 11:20 PM, Drew McDermott wrote:

>
>
>> [Shi, Xuan]
>
>> ... I know I said something different from the others. Such as  
>> what is
>> service composition? My definition is different from the so-called
>> "standard" meaning, but I think it is more realistic and  
>> understandable for
>> all users who are not programmers and AI professionals to consume Web
>> services.
>
> This admission is simply astonishing.  I pointed this discrepancy out
> to Xuan months ago in private correspondence.  The SW community
> disagrees about many aspects of the "service composition problem," but
> everyone agrees it involves computers doing some sort of combination
> of solutions of small web-service problems in order to solve bigger
> problems.  Because the English word "compose" is ambiguous, and
> because Xuan came into this area as an outsider, he originally thought
> it meant human composition of web-service requests (as one would
> compose an SQL request, for instance).  An honest misunderstanding.
>
> But it is not an acceptable response to such a revelation to continue
> to use the semi-standard term in one's nonstandard way.  To do so is
> to guarantee that any discussion using the term will be meaningless,
> chaotic, and ultimately acrimonious.  (The more so if there are
> _other_ terms that are being used in nonstandard ways; who knows?)
>
> I don't see why anyone would pursue this any further.
>
> -- 
>
>                                          -- Drew McDermott
>                                             Yale University
>                                             Computer Science  
> Department
>
>