Joint Committee Minutes 25 September 2001

This page summarizes the telecon for the Joint US/EU Committee on Agent Markup Languages held from 1300 to 1400 PDT on 25 September 2001. These minutes were prepared by the chairman, and were approved during the 2 October telecon.

Participants

Announcements

No announcements this week.

Last Week's Minutes

The minutes from September 18 were approved by those present.

DAML+OIL Submission

No news to report.

Query Languages

Richard introduced his comparison of DQL and RQL. He noted that RDQL doesn't support inference, so it is of less interest to us than RQL and DQL. For DAML+OIL, we're primarily concerned about inference and entailment.

Peter noted that RDBMSs are restrictive with respect to properties, while DAML+OIL is permissive.

Query Premise

Frank asked about the motivation for including a set of DAML+OIL statements as a query premise in DQL 0.1, and whether there was a precedent. This is relatively common in theorem provers, and is typically used to ask questions about about a new prototypical instance, e.g. "how many parents does a person have?". Pat noted that this was common in RKF, but that we may want to separate query from more general-purpose question answering language.

The Stanford JTP implmementation supports checkpointing with rollback, and uses this to handle premises.

In general, premises are useful for accessing subsumption style reasoning with variable bindings. They can also be used for "what if" analyses.

Direct Operator

Frank noted that being able to determine direct subclassOf relations is critical for software tools and query relaxation. The RQL direct operator (^) is equivalent to a query with negation: "is X a subclass of Y and is there no other class that is an intermediate subclass between X and Y".

The direct operator can introduce non-monotonicity in an open world, as noted earlier. Pat suggested that having non-monotonic constructions in the query language is probably OK, but non-monotonic conclusions are not.

Richard noted that identifying direct relationships was needed in OKBC. He suggestd that we might want to separate structural and entailment queries.

There was no consensus on supporting the direct queries.

Disjunctions and Negation

Ian noted that disjunctions of conjunctive queries shouldn't add to complexity. There was consensus that negation was much less used and also more complex.

ACTION (Ian): investigate complexity of disjunction and atomic negation

Duplicate Bindings

Mike raised the need for an equivalent to SQL's select distinct, eliminating duplicate bindings to reduce client and network overhead. In some cases, you want duplicates; in others, you don't. For example, given the query "what books did Pat buy?", you might or might not be concerned that the same book was purchased twice.

Peter noted that this is like DBMS projection, and gets even more complicated with inference.

Richard noted that DQL currently returns unique sets of bindings for all variables mentioned in the query.

RESOLVED: DQL should provide some mechanism for returning subsets of the variables mentioned in the query. The user can get multiple occurances of the same bindings for some variables by adding the variables occuring along multiple distinct paths.

ACTION (Richard): summarize discussion in an email message.

Multiple Names

Peter had raised the issue of multiple names. Ian noted that query language for FaCT always returns a set of names, which is usually a singleton set.

RDF Core WG

The W3C RDF Core WG agreed last week to drop the prohibition against subClassOf cycles. They haven't explicitly addressed subPropertyOf yet, but are expected to follow suit.

There has also been some discussion about whether rdf:parseType="daml:collection" is to be interpreted as a string or as a QName.

Telecon Schedule

There was some discussion about changing the time (and/or day) for our telecons to better accommodate some of our new members.

"Quick fix" proposals of making the telecon 2 or 4 hours earlier didn't work even for those present.

ACTION (Mike): poll the group for a possible new time

Next Week

We'll continue the query language discussion, focusing on Richard's second message. Richard will investigate JDBC and report on its relationship to DQL.

We'll continue the discussion regarding daml:collection.

Several folks (Ian, Dieter, Frank, and Stefan -- Pat and Deb were also invited) will be partcipating in the NSF/EU Semantic Web strategy meeting in France during next week's telecon. We decided to have a telecon anyway. They'll provide a report on October 9.

Links

IRC
Kelly Barber's raw notes
last week's minutes
Joint Committee home page

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