- From: Ian Horrocks <horrocks@cs.man.ac.uk>
- Date: Wed, 14 May 2003 18:27:09 +0100
- To: Jeremy Carroll <jjc@hpl.hp.com>
- Cc: www-webont-wg@w3.org
On May 13, Jeremy Carroll writes: > > > (This message predates > http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0168.html > and gives a different tale on datatypes - I will look at the decision in the > issues list next > ) > > Hmm it seems I will have to do more work than I had been planning at this > stage ... > > > 4.2.1 (suggestion) Might be better to allow a syntax checker to > > ignore some lower levels, eg I'd be very happy with an engine that > > would say 'DL' for Lite docs as well as DL-not-Lite ones. > > I am not accepting this suggestion. > > Rationale: > > that may be a useful tool, there are many useful tools we could have defined. > The one we did define is not, prehaps, very useful. > > I do not believe the motive for these definitions is their fundamental > utility but more they are simple to state and give developers a common > target. Given the (im)maturity of the area we would then expect developers > to have their own spin on other functionality. > > As an example, the syntax checker I wrote gives error messages consisting of > (hopefully) small subgraphs that are not in OWL Lite, or not in OWL DL, if so > desired. I hope this is useful, but I wouldn't expect it to be standardised. > > I have already had demand for an OWL parser , which I take to be a device > that returns an abstract syntax tree from RDF/XML output. That I think is > what some users will want - however I am not convinced that we should make > the abstract syntax obligatory in such a way. > > I believe that the current syntax checker specification is sufficient to give > some idea of what we expect, without being overly spelled out (i.e. the > spelling out that we have done is clearly insufficient for most purposes). > > > 4.2.2 > > Er... I'm embarrassed that I don't know the answer to this, but is it > > really the case that any Lite ontology is consistent in Lite iff it > > is consistent in Full? Is there a proof of that somewhere? > > Sandro suggested deleting the line > "Every OWL Lite consistency checker can be trivially transformed into an OWL > Full consistency checker. " > > I take the rest of the note to follow from the semantic layering results and > the correspondence theorem. Also my thinking - seems trivially (lite ont is a DL ont and has same semantics). > (Actually, these results are currently false - > see thread concerning intersectionOf bug). > > > [Added later: I see that you credit Ian with help on this section. I > > think the three of us could agree on a suitable wording reasonably > > quickly.] > > I think the usual convention is that Ian gets the credit and I get the blame! :-) > Any faults should be attributed to me. > > > So I would suggest the following: > > distinguish a consistency checker (responses are Con/unknown) from an > > inconsistency checker (Incon/unknown), and define 'complete' for both > > of them thus: > > A[n in]consistency checker is complete if, whenever its input > > document is [in]consistent, it would eventually (given unlimited, but > > finite, resources of memory and time) return the answer > > '[In]consistent'. > > Then say a checker is decisive (new word, avoids the 'decision > > procedure' terminology) if it is both a complete consistency checker > > and a complete inconsistency checker. Then remark that there are no > > decisive checkers for OWL-Full but there are for OWL-Lite and OWL-DL. I am very much against our inventing new terms like "decisive". The term complete seems perfectly correct here - we could add complete and terminating if you insist, but the "terminating" part is often taken for granted when completeness is claimed (for implementations at least). I have to dash now to catch a flight - more later. Ian > > > > Simpler (editorial) option: replace 'complete' with 'decisive' (or > > some other word which is not a standard logical term) in current > > definition and rest of text. > > I am inclined to do the second of these, I will give more detail after I have > touched the text. > IMO we already have too many consistency checkers defined (5) Your first > suggestion would increase this number. > > > Another idea: allow three responses (four for a double-sided checker) > > where 'unknown' means 'dunno, run out of energy' and 'indeterminate' > > means 'can't figure because of network error or some such'. Then you > > could allow a complete implementation to return 'indeterminate' but > > not 'unknown'. Roughly, this distinguishes inability to answer based > > on internal versus external issues. Completeness relative to > > externals is obviously impossible to guarantee, is the point. > > Sandro, too, wanted some change on this point. (He wanted > "ResourceLimitExceeded" as a legal response). > > How about: > [[ > Consistency checkers MAY return additional information. > For example, the response 'Unknown' may have special cases > such as 'Unknown (time-limit-exceeded)', ''Unknown (memory limit exceeded)', > 'Unknown (infinite model checking not implemented)'. > ]] > > > Im a bit worried about stating completeness in the presence of > > datatypes. > > So was I. > > > Does this mean that consistency wrt one set of datatypes > > is different from consistency wrt a different set? > > ******* > This text here was written early this morning and gives one view of what a > datatype theory is. > The msg > http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0168.html > was written later after I had reread the S&AS text on datatype theory. > I would appreciate someone else opinion as to which of these readings is > correct. > ************** > > I think it might be. > > For example, xsd:NMToken is a subdatatype of xsd:string. > However, we do not require implementations to know that. > > Thus > > <FunctionalProperty rdf:ID="dp"> > <owl:Thing> > <dp rdf:datatype="&xsd;NMToken">1</dp> > <dp rdf:datatype="&xsd;NMToken">01</dp> > </owl:Thing> > > is inconsistent if you know that the l2v mapping of the datatype is the > identity. But if you don't then maybe xsd:NMToken is derived from integer, > and the file is consistent. > > As I understand it, S&AS, with a datatype theory that does not include > xsd:NMToken, makes the above example consistent. With a datatype theory that > does include xsd:NMToken then the above example is inconsistent. > > I have not provided any tests for the former statement, or analogous; and > don't currently intend to. > > > I think > > this needs to be spelled out a little more carefully (define it wrt a > > datatype API, maybe? ) > > I could add a statment like > [[ > An OWL consistency checker MUST provide a means to determine the > datatypes supported by its datatype theory; for example, by listing > them in its supporting documentation. > ]] > > > The final NOTE in this section refers only to DL and Lite: why? This > > is characteristic of all forms of completeness. > > We only agreed to define complete OWL Lite and OWL DL consistency checkers > (Manchester f2f). There is no complete OWL Full consistency checker (your > term 'decisive') since OWL Full is not decidable. > > >Why are there not parallel definitions of an entailment checker, with > >conforming definitions of completeness, correctness etc. ? It would > >seem to be easy enough to state these in parallel to those in section > >4.2. These notions would be a lot more useful in practice > > I notice you missed the Manchester f2f - we did have a fairly heated debate. > (The Friday morning session ended somewhat abruptly with most of the current > ideas on the table but not with consensus - I had a long lunch catching up > with an old friend, and when I returned the group had made much more progress > without me). > > So the brief response is "WG decision" > > There was reluctance to have any software conformance statements. > There were others who strongly desired software conformance statements. > > There was agreement that we were obliged to provide document conformance > statements. > The agreed software conformance statements hang off the document conformance > statements. > > As one of the people in favour of s/w conformance statements I came away > happy for the following reasons: > > - anyone building a consistency checker will have the bits and pieces to > construct an entailment tool > - it is (slightly) less clear what an entailment tool should do > - assuming an entailment tool is genuinely useful someone who has built a > consistency checker to get the OWL conformance sticker, will also supply an > entailment tool. > - given that we have entailment tests in the test suite it is likely that > most tool developers will, internally at least, make the effort to provide > such functionality, if only to take full advantage of the test suite. > - as test editor I could ensure that many tests were consistency and > inconsistency tests, and have fewer entailment tests (This is a policy I have > actively pursued since the Manchester f2f). > > > Jeremy > > >
Received on Wednesday, 14 May 2003 16:15:24 UTC