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Re: Why would the semantic web services need new logic formalisms?

From: Bijan Parsia <bparsia@isr.umd.edu>
Date: Sat, 24 Mar 2007 20:19:25 +0000
Message-Id: <FF254FDB-546C-4A43-B1CB-2CEC35CD61BA@isr.umd.edu>
Cc: public-sws-ig@w3.org
To: Jukka Villstedt <jukka.villstedt@gmail.com>

On Mar 23, 2007, at 10:01 AM, Jukka Villstedt wrote:

> Hello,
>
> I'm trying to understand the semantic web services effort in  
> general. I have read about OWL-S, WSMO, SWSF and SAWSDL. There  
> seems to be an urge to define new logic formalisms and reasoning  
> techniques to solve the problems.

Or reuse old ones.

> I don't quite understand this.
>
> The overall goal of semantic web services (SWS) is that we could  
> express implicit

Implicit?

> goals and the SWS machinery would then realize these goals using  
> the concrete services that are advertised in the web. To express  
> these goals we need some domain specific ontology.

Well, we need a way to represent the goal.

> To describe the available services we must also use the same or  
> some compatible ontology.

Yep. At least if we are going to hook the services up to achieving  
the goals.

> If the ontology's are different there must be some mapping from one  
> ontology to other.

And how do you express that?

> The famous example is that we want to purchase a trip from one city  
> to another. To me it seems entirely feasible to define an ontology  
> about travel services such as plane or train lines and to run query  
> about these services for example with some SPARQL query engine.  
> This query may have to be distributed, but distributed queries are  
> an old and I guess well understood problem domain. The overall  
> consensus among the SWS research field seems to be that this kind  
> of simple approach does not work.

Who says that?

> Instead a heavy weight logical formalisms are developed.

Well, if the SPARQL query is run against OWL ontologies, for example,  
then there is "heavy weight logical formalism" already in play. So  
you need to be more precise in setting up your contrast classes.

SPARQL itself is a fairly complex logical formalism.

> For example it is proposed that a rule language is needed for  
> expressing that a certain type of credit card needs to be provided  
> to use a certain service. To me this seems simply a matter of  
> defining such an ontology

In what formalism?

> in which this requirement can be expressed.

That's the issue, eh? It has to be expressed in a manner sufficient  
to allow for the desired behavior.

> The set of valid credit cards could be a property of the service  
> and the agents or mediators that understad the ontology must know  
> that any valid request must include a pointer to one of these  
> credit cards.

And how do you accomplish all this?

> The automatic service composition may be a good application domain  
> for classical planning algorithms. Simple planning based on input  
> and output types of services is certainly possible. But other  
> applications of logic programming paradigms in the field of SWS do  
> not seem to be that well justified.

While that may be true, I don't see that you've established the  
point. You (implicitly) *claim* that "ontologies" are more  
lightweight, but without any description of the ontology language,  
you don't get to assume that.

Plus, take, just for example, OWL-S. You describe some of the aspects  
of a service using fairly vanilla OWL. But preconditions and effects  
generally require a bit more machinery.

> It seems that the goal of extensive formal service descriptions is  
> that services that are described with them could be used by a  
> software agent that is not specifically developed to understand the  
> related domain ontology.

Well, if part of the related domain ontology are descriptions of the  
*actions* one might take and their *consequences*, then perhaps. It  
might be better to say that service descriptions are one way *you  
build domain specific software agents* with a certain level of  
flexibility. That's certainly one view of, e.g., HTN planning.

> I think a more appropriate or at least practical focus should be on  
> how to define, and automatically apply ontology mappings and other  
> mediators rather than trying to cope without shared ontologies.

Again, what's in your ontologies? If they don't have enough to  
support reliable manipulationg, then there's no point. If they do,  
they're are going to be roughly expressive, I'd warrant, as at least  
the weaker current description languages.

> The formalisms such as SWSL and WSML can be seen as an effort to  
> develop tools for ontology mapping, but there is a danger that we  
> over emphasize declarative programming paradigms. If declarative  
> programming would be applicable to large scale real world problems,  
> I would expect there to be more evidence on that.

SQL, XSLT, XQuery, XML Schema, BPEL (sorta), CDL....

In any case, popularity doesn't determine applicability.

> I'm in no way an expert on logic programming so I may have missed  
> something here.
>
> I hope there could be some good discussion on these topics to  
> clarify the overal picture.

Hope this helps.

Cheers,
Bijan.
Received on Saturday, 24 March 2007 20:19:28 UTC

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