- From: Dan Connolly <connolly@w3.org>
- Date: Wed, 27 Jun 2001 00:55:02 -0500
- To: Graham Klyne <Graham.Klyne@Baltimore.com>
- CC: pat hayes <phayes@ai.uwf.edu>, Brian McBride <bwm@hplb.hpl.hp.com>, w3c-rdfcore-wg@w3.org
Graham Klyne wrote: [...] > (1) Unknown binding... [...] > Following this line, any pair of names can bind to the same object in the > domain of interpretation that matches what we know about them, so from your > examples: > > [[[ > <http://skolem.example#432oj34oij2o3ijo23j> > <http://purl.org/dc/elements/1.1/title> "Fractals Everywhere" . > : > ]]] > > and > > [[[ > <http://booksRus.example/inv2001-06-25#item342323> > <http://purl.org/dc/elements/1.1/title> "Fractals Everywhere" . > : > ]]] > > Can be matched by an interpretation in which > <http://skolem.example#432oj34oij2o3ijo23j> and > <http://booksRus.example/inv2001-06-25#item342323> indicate the same value. But that's the case only for *some* interpretations; using the formula in existentially-quantified form, before skolemiziation, *all* interpretations that satisfy the bookseller's database satisfy the query; i.e. going from one to the other is a valid inference. > The problem here seems to be one of computation rather than logic: if > *any* pair of constants must be tested to see if they match the same > conditions, then the search space becomes impossibly large for a practical > problem. No, it's a problem of logic: going from (title item34 "f a") to (title sk1 "f a") is not a valid inference; but going from (title item34 "f a") to (exists (?x0) (title ?x0 "f a")) is. > So the information you want to preserve would seem to be that > only some of the names are to be considered as possibly equivalent to other > names, in order that the query can be resolved in reasonable time. > > (2) Variable terms > > The model theories I have seen distinguish between constant names and > variable names: the meaning of a constant name is defined entirely by an > interpretation. The meaning of a variable name is defined by the > interpretation AND some variable substitution. exactly. > It seems to me that your "anonymous" node could be viewed as a node named > by a variable. The statement containing such a name would be satisfiable > under a given interpretation iff there exists a substitution of a value in > the domain of interpretation for the variable that makes the target > expression true. Yup; that's what I'm saying when I claim that _:g0 <http://purl.org/dc/elements/1.1/title> "Fractals Everywhere" . can be writtein in KIF as (exists (?x0 ) (PropertyValue http\:\/\/purl\.org\/dc\/elements\/1\.1\/title ?x0 "Fractals Everywhere") ) > The query then becomes the problem of finding a variable substitution that > satisfies an interpretation defined by the database. aka proving a theorem of the form "there exists...". -- Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Wednesday, 27 June 2001 01:56:37 UTC