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ISSUE-26: SimpleExtension proposal

From: Guus Schreiber <schreiber@cs.vu.nl>
Date: Tue, 29 May 2007 15:25:59 +0200
Message-ID: <465C29E7.2030707@cs.vu.nl>
To: SWD WG <public-swd-wg@w3.org>

ACTION: Guus revise his ISSUE-26 proposal to account for other options [recorded in http://www.w3.org/2007/04/24-swd-minutes.html#action07] 

All,

Below is my SimpleExtension proposal for isue 26 (relations between labels). I haven't had time to check 
the syntax of the examples or put it on the Wiki. 

Guus


SKOS ISSUE-26 Relations between Labels: "SimpleExtension" Proposal

This is a proposal for resolution of SKOS ISSUE-33. 

0. Summary

The proposal extends SKOS with the possibility to define a term as a
resource, such that statements can be made about it. To this end we
introduce the class skos:Term plus the corresponding properties (pref,
alt, hidden) which link a concept to a term. 

The property skos:relatedTerm can be used to express relations between
terms. Applications will typically specialize this to define
particular lexical relations. 

The proposal ensures OWL DL compatibility. 


1. Vocabulary

The proposal introduces the following new vocabulary:

  skos:Term

  skos:prefTerm
  skos:altTerm
  skos:hiddenTerm

  skos:relatedTerm


2. Axiomatic Triples

The following triples are added:

  skos:Term rdf:type rdfs:Class.

  skos:prefTerm rdf:type rdf:Property.
  skos:prefTerm rdfs:domain skos:Concept.
  skos:prefTerm rdfs:range skos:Term.

  skos:altTerm rdf:type rdf:Property.
  skos:altTerm rdfs:domain skos:Concept.
  skos:altTerm rdfs:range skos:Term.

  skos:hiddenTerm rdf:type rdf:Property.
  skos:hiddenTerm rdfs:domain skos:Concept.
  skos:hiddenTerm rdfs:range skos:Term.

  skos:relatedTerm rdf:type rdf:Property.
  skos:relatedTerm rdfs:domain skos:Term.
  skos:relatedTerm rdfs:range skos:Term.


3. Semantic Conditions

* A skos:Concept has at most one skos:pretTerm relation

    skos:prefTerm rdf:type owl:FunctionalProperty.

* A skos:Concept must be the subject of at least one one skos:prefLabel or
  skos:prefTerm triple. 

    NOTE: there seems to be no reason to forbid mixing of label and
    class approach. So the "or"is not an exclusive or.

4. Consistent Examples

EXAMPLE 1

The example below shows two terms for a concept, where one term is defined
as the acronym of the other term. 

  ex:who 
    rdf:type skos:Concept;
    skos:prefTerm ex:who1.
    skos:altTerm ex:wh02
  ex:who1 
    rdf:type skos:Term;
    rdfs:label "World Health Organization"@en-us;
    rdfs:label "Wereldgezondheidsorganisatie"@nl.
  ex:who2 
    rdf:type skos:Term;
    rdfs:label "WHO"@en.
  
  ex:acronymOf 
    rdf:type rdf:Property;
    rdf:subPropertyOf skos:relatedTerm.
  
  ex:who2 ex:acronymOf who1.
       

5. Inconsistent Examples

All triples that obey the constraints posed by the RDF/OWL definitions
are consistent.


6. Entailment Rules

DISCUSSION: should we have an entailment rule that says something
like:

  for every <x>Term statement (where x can be either pref, alt or
  hidden) tools are allowed to assert a <x>Label triple for each of
  the rdfs:label statements of the object of the <x>Term statement.

So from example 1, applications derive  the following additional triples:

  ex:who 
    skos:prefLabel "World Health Organization"@en-us;
    skos:prefLabel "Wereldgezondheidsorganisatie"@nl;
    skos:altLabel "WHO"@en.

DISCUSSION: should the inverse also be true? E.g should applications be
allowed to derive the following: 

  ex:who 
    skos:prefLabel "World Health Organization"@en-us;
    skos:prefLabel "Wereldgezondheidsorganisatie"@nl;
    skos:altLabel "WHO"@en.

  entails

  ex:who
    skos:prefTerm 
      [a skos:Term 
        rdfs:label "World Health Organization"@en-us;
        rdfs:label "Wereldgezondheidsorganisatie"@nl];
    skos:altTerm 
      [a skos:Term 
        rdfs:label "WHO"@en].

NOTE: the difference with example 1 is here that the instances of
skos:term are represented as blank nodes. 

NOTE: to express these entailments it might be easier to define a
superproperty for the both the Label and the Term properties. 


7. Syntactic Constraints

@@todo


8. Discussion

The objective of this proposal is allow term relations, while
preserving compatibility with the label approach. 

The main alternative would be to drop the semantic constraint on the
<x>Label properties to be an owl:DatatypeProperty. This would make the
following example consistent:

  ex:who 
    rdf:type skos:Concept;
    skos:prefLabel ex:who1.
  ex:who1 
    rdf:type skos:Term;
    rdfs:label "World Health Organization"@en-us.

even in combination with:

  ex:who 
    skos:prefLabel "World Health Organization"@en-us;

One can view this of the MinimalFix proposal but has two
disadvantages: 
- ambiguity wrt the range of the skos:<x>Label properties
- incompatibility with OWL DL, as it is not possible to define the
label properties as either an objector a datatype property. 

The SimpleExtension proposal preserves OWL DL compatibility. 

The entailment rules mentioned under 6 are meant to preserve
interoperability between vocabularies that use different approaches to
represent lexical labels.





-- 
Vrije Universiteit Amsterdam, Computer Science
De Boelelaan 1081a, 1081 HV Amsterdam, The Netherlands
T: +31 20 598 7739/7718; F: +31 84 712 1446 
Home page: http://www.cs.vu.nl/~guus/
Received on Tuesday, 29 May 2007 13:26:41 GMT

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