1. DAML Language Breakout Deborah L. McGuinness Knowledge Systems Laboratory Stanford University www.ksl.stanford.edu 2/15/01

2. Knowledge Systems Laboratory, Stanford University2Topics  Reification  Defaults/Non-Monotonicity  Proof Checking  Concrete vs. abstract domains (pre-defined types vs. user-defined types) (datatypes vs. classes)

3. Knowledge Systems Laboratory, Stanford University3Reification (from dictionary: To regard or treat (an abstraction) as if it had concrete or material existence.)  Requirement: Need to make statements about statements.  Extensive discussion concerning potential pitfalls, usage in rdf, relationship to RDF, requirements  Conclusion – if we include reification, we will expect problems  Speculation – we may not be able to avoid modalities as long as we might have thought.

4. Knowledge Systems Laboratory, Stanford University4Defaults/Rules  Currently no default/rule/negation as failure capability in DAML+OIL  Agreement that some solution is needed  Consider some mechanism on top of the core language  Observation that negation as failure in rule systems has long history of usage, tractability, etc.  Action Items – form rule mailing list (Ben Grosof will seed the list)  Small group followup meeting on topic

5. Knowledge Systems Laboratory, Stanford University5 Proof Checks  Discussion on non-monotonicity led to a discussion of possibly checking non-monotonic proofs  Discussion followed on proof checks of (possibly partial) deductions  Can either trust reasoners or just check their proofs  Proof checking requires tractable proof checking systems  Followup among interested parties

6. Knowledge Systems Laboratory, Stanford University6 Concrete Data Types  Consensus that concrete data type (numbers, strings, etc) are necessary  Consensus around basic proposal initiated by Horrocks and Patel-Schneider  Technical discussion about rdf syntax.  Peter (and Ian and Frank) will provide a modified proposal taking into account Connolly’s document http://www.w3.org/2001/01/ct24 http://www.w3.org/2001/01/ct24  Expectation is that this will be included in the language prior to semantic web activity

7. Knowledge Systems Laboratory, Stanford University7 Other issues?  Send email to rdf-logic mailing list (or dlm@ksl.stanford.edu)

8. Knowledge Systems Laboratory, Stanford University8Background  Attended by most of ad-hoc committee (physically or virtually)  Solicited feedback on current language and wishes for modifications/extensions  No feedback on current language other than extensions