- From: pat hayes <phayes@ai.uwf.edu>
- Date: Tue, 11 Mar 2003 17:17:21 -0600
- To: w3c-rdfcore-wg@w3.org
- Cc: timbl@w3.org
Summary of the semantic alternatives for RDF reification. --------------------------- A reification assertion such as aaa rdf:subject bbb . is saying that something is the subject of something else which is an RDF triple. There are at least two orthogonal dimensions on which one can choose alternatives about what exactly these 'somethings' are. aaa might refer to a triple as an abstract grammatical form, or it might refer to a particular occurrence of a triple in some actual document somewhere. This has been referred to as the 'statement/stating' difference. bbb might refer to a piece of syntax - the actual subject 'node', or subject token in a document - which occurs in the RDf graph, or it might refer to the thing that is considered to be the subject of the proposition expressed by that triple. This has been referred to as the 'de-dicto/de-re' difference. This can be dramatized by asking: is the rdf:subject of the triple ex:Mary ex:had ex:littleLamb . a girl or a uriref (respectively de dicto or de re) ? These two choices are independent, but each influences the significance of the other. Currently, the semantics document recommends that one should interpret this vocabulary so that aaa is interpreted as a stating, ie referring to a concrete occurrence of a triple rather than an abstract form; and that bbb should be interpreted de re, ie as referring to Mary rather than to Mary's URIref. The reasoning behind these choices are as follows. Statings allows one to associate provenance information with triples in a document a document by using reification to talk about the triples. This would be impossible (meaningless) if we imposed the 'statement' interpretation. Such uses of reification form a large class of actual use cases. On the other hand, if someone wants to describe the abstract grammatical form of a statement, this can be done by using a particular instance of it as an exemplar for the abstraction, eg by associating a bnode with the reification by a property like <ex:abstractformOf>. The de re interpretation allows reifications to use the same conventions for interpreting URIrefs as other triples, so that a URIref used as an actual subject node, and the same URIref used as the object of an rdf:subject assertion, have the same meaning. In contrast, the de dicto interpretation would require a reasoner to distinguish these two uses, using some extra-RDF convention such as quotation, or else require that subjects and objects of reified triples be given distinct URIrefs which are understood in a 'meta' sense to refer to the actual URIrefs in the subject and object position of the reified triple. Neither of these formal techniques have emerged in practice, suggesting that the de re interpretation in fact codifies existing intentions of users. One objection to the de re interpretation is that it does not allow for the adequate representation of propositional attitudes such as belief. This is controversial (see the discussion of the Russellian theory in http://plato.stanford.edu/entries/prop-attitude-reports/) , but in any case there is ample experience which suggests that the de dicto interpretation would produce other problems with the representation of such ideas, and that an fully adequate representation of propositional attitudes is unobtainable using reification alone. Pat -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes s.pam@ai.uwf.edu for spam
Received on Tuesday, 11 March 2003 18:17:21 UTC