F2F Day 2: 2001-08-02 RDF Schema 1.0 Discussion Progressing RDF Schema: - dan brickley (rdfs editor) - brian mcbride (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...] Art: is there any evidence that anyone has done an implmentation that is contrary to this proposal? (how much will this hurt current implementation if we change this?) Ron: is it possible that we have something different than rdfs:domain that will solve this problem? Danbri: if possible I'd like to discuss some of these issues without opening up the issue of different namespaces. Vote on Proposal: (look into Jan's notes on status of vote) 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 [discussion point...] 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 change to current specification REASONS: * 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: * A task force to investigate the DAML+OIL approach for using XML Datatypes * Seek implementor feedback on this explicitly in our next WD NOTE: We don't consider this as a requirement for the next version of the draft - 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: * Providing some explanatory text. REASONS: * We don't believe this is a problem. * 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 (subPropertiesOf) properties are prohibited PROPOSAL: * Open this issue (Frank M.) * Flag this in the next draft ... flag the point that we're thinking of removing this retriction and to see how this affects implementation * Action (Pat) to go back to DAML+OIL with this - rdfs-subPropertyOf-semantics: The inheritance semantics of the subPropertyOf relationship needs to be clarified. PROPOSAL: * clarify prose (subProperties inherit domain and range of their superProperties) - rdfs-subClassOf-a-Property: Clarify whether a Property can have a subClassOf property, and if so, what that would mean? PROPOSAL: * do nothing with respect to the next working draft * clarify this issue by considering "are rdf:Property and rdfs:Class disjoint"? REASON: * with the range/domain fix, this becomes: are Property and Class disjoint - rdfs-online-char-encoding: There is problem with the character encoding of the online RDF Schema. PROPOSAL: * Editor to fix the encoding REASON: * editorial oversight * spend no time here talking about whether to change ns uri - rdfs-versioning: RDF Schema does not deal adequately with versioning. PROPOSAL: * Do nothing REASON: * known hard problem * Note that the problem is very difficult to solve, and outside of the scope of this working group. Propose to not solve this problem. - rdfs-transitive-subSubProperty: Is a sub-property of rdfs:subPropertyOf necessarily transitive? PROPOSAL: * Make no changes in next version of the draft - 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.