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private review of Profiles, Section 4.3 (OWL 2 RL/RDF rules)

From: Michael Schneider <schneid@fzi.de>
Date: Thu, 16 Apr 2009 22:39:53 +0200
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A00125FA57@judith.fzi.de>
To: "OWL 2" <public-owl-wg@w3.org>
Hi!

Here is a last minute review of the OWL 2 RL ruleset in Section 4.3 of the Profiles document.

Michael
 
* [editorial, missing explanation] Intro text, 2nd par: It's explained what the "propositional symbol 'false'" means in the tables. What's missing is an explanation of the symbol 'true', which appears several times as the premise of rules (e.g. in Table 5, rule "prp-ap").

* [editorial, typo(?)] Text preceding Table 4: "it defines the equality relation on resources owl:sameAs as being reflexive,...". Is there a grammatical error in this sentence ("on resources owl:sameAs")?

* [editorial, possible confusion] The rule "eq-diff2" in Table 4 contains the triple "T(?zi owl:sameAs ?zj)" in the premise, and the third column contains the text_ "for each 1<=i<j<=n". There are two possible ways to understand this: (a) this table entry stands for several rules, and (b) it's one rule with several such triples on the LHS. I suppose (a) is meant, but this should be made clearer (originally, I thought it was (b), till I found that this rule would then be strange). Same for several other rules: prp-adp, cls-uni and cax-adc.

* [technical, change request] In another mail I suggested to remove the typing triples of the two rules for negative property assertions, see <http://lists.w3.org/Archives/Public/public-owl-wg/2009Apr/0341.html>.

* [technical, missing(?) rules] I wonder why there are no rules for owl:hasSelf, which mirror the two rules for owl:hasValue. Have these been forgotton? They would be:

  cls-hs1:
  IF: 
      T(?x, owl:hasSelf, "true"^^xsd:boolean)
      T(?x, owl:onProperty, ?p)
      T(?u, rdf:type, ?x)
  THEN:
      T(?u, ?p, ?u)

  cls-hs2:
  IF:
      T(?x, owl:hasSelf, "true"^^xsd:boolean)
      T(?x, owl:onProperty, ?p)
      T(?u, ?p, ?u)
  THEN:
     T(?u, rdf:type, ?x)

* [technical, change request] All the cardinality restrictions in Table 6 contain literals of the form "n"^^xsd:nonNegativeInteger. In believe this asks for trouble, since presumably only a small fraction of all OWL/RDF documents will use xsd:nonNegativeInteger for building cardinality restrictions. In comparison, the reverse RDF Mapping uses a function "NN_INT(n)" as a placeholder for all kinds of non negative integer definitions. I suggest to use this function in RL, too. This would be ok for the relationship to the RDF-Based Semantics, which isn't restricted to a single number datatype, either, but only talks about the /value space/ of xsd:nonNegativeInteger. 

* [technical, missing(?) rules] Where are the exact-cardinality variants of all the max-cardinality restrictions (including max-QCRs)? This looks like a significant omission to me that may lead to problems in practice.
 
* [editorial, incoherent format] The rule "cls-oo" in Table 6 has as its consequent: "T(?yi, rdf:type, ?c)", and the third column says "for each 1<=i<=n". Make it coherent with the other rules with more than one result triple (eg. cls-int2), by replacing this single template triple by "T(?y1, rdf:type, ?c) T(?y2, rdf:type, ?c) ... T(?yn, rdf:type, ?c)"; and drop the "for each ..." text in the third column (this will also avoid confusion with other occurrences of "for each" entries in the third column, which have a different meaning than this one).

* [change, redundancy] In Table 9, the rule "scm-cls" has several result triples, including "T(?c, owl:equivalentClass, ?c)". I suggest to drop this equivalence triple, since it is redundant, due to the rdfs:subClassOf triple and rule scm-eqc2. I know, we don't claim redundancy-freeness for the ruleset, but IMHO this one is almost provocatively redundant. ;-) Analog for the rules scm-op and scm-dp.

--
Dipl.-Inform. Michael Schneider
Research Scientist, Dept. Information Process Engineering (IPE)
Tel  : +49-721-9654-726
Fax  : +49-721-9654-727
Email: michael.schneider@fzi.de
WWW  : http://www.fzi.de/michael.schneider
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Received on Thursday, 16 April 2009 20:40:38 GMT

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