Web Services and Semantic Web

(Notes from the breakout session on April 10, 2001 @ W3C WS Workshop)


Arindam Banerji axb@hpl.hp.com
Tim Berners-Lee  timbl@w3.org
Suresh Damodaran suresh_damodaran@stercomm.com (Scribe)
Rael Dornfest rael@oreilly.com
Gerald Edgar gerald.edgar@boeing.com
David Fallside fallside@us.ibm.com
Scott Isaacson sisaacson@novell.com
Ken Laskey Kenneth.J.Laskey@SAIC.com
Bob Marcus marcus@roguewave.com
Noah Mendelsohn noah_mendelsohn@lotus.com
Nilo Mitra nilo.mitra@ericsson.com
Chalon Mullins chalon.mullins@schwab.com
Klaus-Dieter Naujok knaujok@home.com
Mark Nottingham mnot@akamai.com
Eric Prud'hommeaux eric@w3.org (Chair)
Marwan Sabbouh ms@mitre.org


Early on it was decided that the goal of the meeting is to
(a) define the terms Web Services and Semantic Web, and
(b) define the relationship between the two.

Web Services

Participants tried to answer two questions at varying times. First, what is a web service; second, how to specify a web service. Below, I will describe the discussions as such.

What is a web service?

There are several opinions on what a web service is.

To access resources (Sankar)

Is the next component model, just like EJB. WSDL is similar to IDL (Arindam Banerji )

Is a service that exposes its properties using standard Internet protocols. Unlike the tightly coupled client/server model, in web service, the client is not tightly coupled with server (Marwan Sabbouh )

Consists of protocols and services (Bob Marcus)

How to Specify a web service?

This discussion got muddied with the discussion on semantic web as well as RDF. The various opinions on the topic are:

Since web service has a common interface, it is much more like a semantic web. WSDL broke down the pieces (?) Semantic web is much more powerful. In this sense, RDF/Semantic web can represent web services (David Fallside).

RDF model is simpler than XML model (RDF model has no attributes). You can read into objects directly as opposed to XML. A WSDL message could be a semantic model description in RDF. Services and messages among service agents can be described in RDF (Tim Berners-Lee ).

Anything on the web has to "scale." WSDL and other descriptions are semantic web elements. Semantic web/RDF are like meta-data/data. (It looked like Noah is saying that WSDL can be expressed as RDF, though it will not scale- check). Such representation has use in discovery & query. SOAP messages are not semantic web elements (Noah Mendelsohn ).

Truth lies between Tim Berners-Lee  and Noah Mendelsohn . RDF can describe documents with nouns and verbs. Noah is asking whether it can describe adverbs. Web service descriptions can have relationships expressed in RDF. WSDL describes the service itself. (Rael Dornfest )

Semantic Web

In this discussion, an implicit assumption appears to be that RDF will be used to specify semantic web. Ontologies were mentioned to be the next thing (Tim Berners-Lee ), though not much else was heard on ontologies in the rest of the discussion. The opinions on what is semantic web:

Semantic web expresses information in a abstracted model with serializable properties (later on Tim Berners-Lee  said that serializability was not important). Semantic web elements have URI. Semantic web expresses information about web services. Semantic web models will accumulate more information as time progresses. (Tim Berners-Lee )

Semantic web is a model (as opposed to complete & rich descriptions as in UML, MOF, etc.). In addition, semantic web is queriable, and provides bindings (David Fallside)

Semantic web can be thought of as database schemas. Instead of thinking of it as a description language, think of using it for reasoning about the description (Sankar)

To build the next generation Web, we need to add more semantics to content and interfaces. It is likely that an extension of current UML and RDF  will be needed for metadata and modeling. (UML has capabilities for process modeling that would be useful for designing orchestration of Web Services as well as capturing XML semantics).  The OMG is in the process of moving towards a model driven architecture approach that will map UML to Web Services middleware as well as CORBA. Bob Marcusinvited participants to the "Software Services Grid Workshop," (http://www.roguewave.com/groups/CTO/workshop.doc) (Bob Marcus).

We need the definition of objects (on the web?) to be more general (Chalon Mullins)

Semantic web provides the territories to describe where web services will apply (Rael Dornfest ).