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rdf schema notes

From: Dan Brickley <danbri@w3.org>
Date: Thu, 2 Aug 2001 12:33:41 -0400 (EDT)
To: <www-archive@w3.org>
Message-ID: <Pine.LNX.4.30.0108021218490.20076-100000@tux.w3.org>

(drafted notes)


F2F Day 2: RDF Schema 1.0 Discussion

Progressing RDF Schema:

	- dan b (rdfs editor)
	- brian m (chairing)



What are we trying to achieve?
-----------------------------

   - agree a closure of our 2 active open issues
   - seeking working hypotheses on other RDFS issues for next WD
     (see how many we can crank through in ?n minutes)
   - understand the context and status of RDFS

Context:
-------

   * RDF Schema is a W3C Candidate Recommendation. This means W3C
     community consider it "as good as done; need implementor feedback"

   * RDF Issue List, DAML+OIL feedback provide this feedback

   * We waited for XML Schema datatypes; DAML+OIL makes a proposal for
     these in RDF

   * How much flexibility:
	- more flexible than M+S, in that we're not fiddling with a
          "Recommendation";
     	- less flexible: RDFS isn't as contested/buggy, a CR means "almost done"
        - time/resources: we have our work cut out with the model/syntax; if we
           spend a lot of effort on RDFS polishing, we distract from the M+S work.
  * RDF Schema is one major application of RDF Core's Model+Syntax work;
    progressing RDFS is a an important sanity check for the M+S work.


   * W3C context:
	- Other WGs are using this spec (CC/PP, P3P, WAI EARL)
   	- A successor WG is planned
	    to do "RDF Schema 2.0" aka "Web Ontology" (DAML+OIL+???)
	- we did the right thing and waited for XML Schema; now its time
          to get this thing moving again.
        - Simplicity Simplicity Simplicity: XML Schema took 3 years and a
          huge WG to publish a rather complex spec;
            W3C and RDFCore can't afford to do this. RDF Schema's value is
            in its simplicity,
	    and (we hope) genuine extensibility: fancy stuff comes later.
            (3 years ago we discussed class specific constraints,
             intentionally defined classes etc for RDFS; the RDFS design
             leaves these to future work; a WebOnt WG will probably do
             that work).


How to make progress
--------------------


We note:

   * Our next step is not our last step: we work to draft some answers to
     implementor feedback
   * for each of these issues, we need a working hypothesis for our Working Draft(s) *
   * Consensus:
	- we do not need 100% consensus to publish Working Drafts
	- we have a duty to document and acknowledge dissent (within WG,
          W3C and wider community)
   * Strawpoll answers to (some) open issues, edit these into an RDF
     Schema WD, and see how it looks _as a spec_ (for us, and wider
     community; users of rdfs 1.0)
   * There will be opportunities to refine the spec (and decisions) in
     light of further testing
   * If we get strawpoll answers to all issues, Eric will eat a spoonful
     of vegemite.


Opened Issues
-------------
rdfs-domain-and-range: Should a property be allowed more than one
rdfs:range property? What should the semantics of
     multiple domain and range properties be? (Dan Brickley)

PROCESS: We can spend 5, 10, 20 or 45 minutes on this. Or 2 days. But we
         *must* come out of the discussion with an ACTION for the editor.  Or
         we don't go home. (for brian: time mgmnt 10 mins?)


PROPOSAL: 	* conjunctive semantics for domain and for range
		* multiple ranges are not forbidden

[discussion point...]




rdfs-domain-unconstrained: The rdfs:domain and rdfs:range constraints for
rdfs:domain are missing from the RDF
     Schema for RDF Schema (Dan Brickley)

PROPOSAL: 	* editorial oversight




Other RDF Schema Issues
-----------------------

     rdfs-constraining-containers: Should it be possible to constrain the
members of a container to be of a given type?


PROPOSAL: 	* No compelling case has been made for additional features  in 1.0
		* We already allow subclasses of the containers
		* Other languages (DAML+OIL; WebOnt; Prose...) can express those constraints



     rdfs-xml-schema-datatypes: A suggestion that the RDF Schema Spec
     might usefully use XML Schema datatypes in
     examples and/or in some formal specification of the mapping of these
     datatypes into the RDF model.

PROPOSAL:	* Adopt the DAML+OIL implementation as an intial foray
                  into this issue
		* Seek implementor feedback on this explicitly in our next WD



     rdfs-primitive-properties: A suggestion that properties such as
       rdfs:subClassOf, rdf:type and others should not be
       instances of rdf:Property, but should be primitive

PROPOSAL:
		* Not critical path for next working draft
		* The model theory (and associated documentation) tells us
		  what rdfs:Class is an rdfs:Class means.
		   Defer to model theory.




     rdfs-no-cycles-in-subClassOf: Cycles of subClassOf properties are
     prohibited

PROPOSAL:	* Not critical for next WD
		* No change in this draft, but note we're not married to
                  current design




     rdfs-subPropertyOf-semantics: The inheritance semantics of the
       subPropertyOf relationship needs to be clarified.


PROPOSAL:	* Not critical path for next WD; do after Model theory




     rdfs-subClassOf-a-Property: Clarify whether a Property can have a
     subClassOf property, and if so, what that would
     mean?


PROPOSAL:	* with the range/domain fix, this becomes: are Property
                  and Class disjoint
		* strawman: yes they are, so it can't.





     rdfs-online-char-encoding: There is problem with the character
        encoding of the online RDF Schema.

PROPOSAL:	* editorial oversight
		* spend no time here talking about whether to change ns uri




     rdfs-versioning: RDF Schema does not deal adequately with versioning.

PROPOSAL:	* known hard problem; defer.




     rdfs-transitive-subSubProperty: Is a sub-property of
       rdfs:subPropertyOf necessarily transitive?

PROPOSAL: 	* take this to the mailing list / telecon. not good f2f  issue.



     rdfs-clarify-subClass-and-instance: Suggestion of clearer discussion
     of use of subClass and instance relationships
     simultaneously.

PROPOSAL:	editorial wordsmithing needed,




     rdfs-isDefinedBy-semantics: Must the value of an rdfs:isDefinedBy
property be a schema?


PROPOSAL: 	not critical path

     rdfs-editorial: General editorial comments.

PROPOSAL:	so noted.
Received on Thursday, 2 August 2001 12:33:41 GMT

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