- From: Smith, Michael K <michael.smith@eds.com>
- Date: Thu, 14 Feb 2002 14:13:00 -0600
- To: Dan Connolly <connolly@w3.org>, "Peter F. \"Patel-Schneider" <pfps@research.bell-labs.com>
- Cc: www-webont-wg@w3.org
I will display my ignorance with a couple of comments relevant to this topic. 1. If we are to take seriously the goal of providing a formal semantics for OWL that completely includes RDF(S), we need to recognize that it is going to be a difficult task. The formal semantics of RDF(S) is incomplete (containers, reification). 2. One of the things I have been puzzled by has been the apparent enthusiasm for triples as a syntax. Its like saying "I really prefer reading binary". I thought Peter's examples were great. They focus on the difficultly of providing a sensible semantic interpretation for arbitrary sets of syntactic triples. Of course I am exaggerating the enthusiasm for triples. If we look at the 'RDF Model and Syntax Specification' and the DAML+OIL Reference Description, the presentation of examples depends on XML, not triples. We could certainly translate a clean OWL syntax to triples (just as the RDF Model and Syntax Specification document does for RDF). Going the other way, in all possible cases, seems to me problematic. It does not seem to be the case that the official syntax for RDF is defined as triples. When I look at 'RDF Model and Syntax Specification' all I see are the XML serializations. Then there is a description of their translation into triples. But no syntax restricting the set of triples that are permitted. 3. It wasn't immediately clear to me whether the bag example Peter presented is ill-formed RDF (I've spent more time looking at the Model Theory than the Specification). Note that the XML syntax used in http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/, where bag elements are referenced using 'rdf:li', eliminates this problem. Which illustrates why a syntax for containers that includes a notion of scope is much simpler than one that does not. Reading the RDF Model and Syntax Specification we find: Note: The definitions of Bag and Sequence explicitly permit duplicate values. RDF does not define a core concept of Set, which would be a Bag with no duplicates, because the RDF core does not mandate an enforcement mechanism in the event of violations of such constraints. The document also states in the description of containers that there may be at most one triple whose predicate is any given element of Ord and the elements of Ord must be used in sequence starting with RDF:_1 I don't understand what the consequences of violating this requirement would be. We have an open world. The fact that we've got RDF:_1 and RDF:_3 explicitly asserted, but not RDF:_2, could just be an accident of the current state. - Mike Michael K. Smith EDS Austin Innovation Lab 98 San Jacinto, Suite 500 Austin, TX 78701 Work: 512 404-6683 -----Original Message----- From: Dan Connolly [mailto:connolly@w3.org] Sent: Wednesday, February 13, 2002 10:44 PM To: Peter F. "Patel-Schneider Cc: www-webont-wg@w3.org Subject: Re: UPDATE: why RDF syntax is not suitable for OWL On Wed, 2002-02-13 at 17:56, Peter F. Patel-Schneider wrote: [...] > Why Triples are Terrible for Syntax [...the suspence builds...] > None of the above problems are really solvable using RDF triples. A much > better syntax carrier would allow syntax to be represented as tuples or, > even better, as trees. Bummer. I was all set to say "yes, that's a much better alternative!" But I don't see an alternative. Oh well... there's always tomorrow... -- Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 14 February 2002 15:13:14 UTC