- From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
- Date: Mon, 1 Oct 2001 18:37:13 +0100
- To: <w3c-rdfcore-wg@w3.org>
This is really a comment about syntax than about MT. In MT, Pat says: "We understand linear RDF notations such as N-Triples and rdf/xml [RDF/XML] as lexical notations for describing an RDF graph" which seems innocuous enough, and appears to suggest that there is a function from RDF/XML documents to RDF graphs. Unfortunately, there isn't. A test case is: <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:foo="http://foo/"> <rdf:Description rdf:bagID="BAG" foo:a="a" foo:b="a" /> </rdf:RDF> This does not specify which reification, that of foo:a or foo:b comes first in the bag. In not-quite-N-triples the difference between the two legal models is: <#BAG> <rdf:_1> _:j2 . _:j2 <rdf:predicate> <http://foo/a> . <#BAG> <rdf:_2> _:j3 . _:j3 <rdf:predicate> <http://foo/b> . versus <#BAG> <rdf:_1> _:j2 . _:j3 <rdf:predicate> <http://foo/a> . <#BAG> <rdf:_2> _:j3 . _:j2 <rdf:predicate> <http://foo/b> . The whole models is: <#BAG> <rdf:type> <rdf:Bag . _:j0 <http://foo/a> "a" . <#BAG> <rdf:_1> _:j2 . _:j2 <rdf:type> <rdf:Statement> . _:j2 <rdf:subject> _:j0 . _:j2 <rdf:predicate> <http://foo/a> . _:j2 <rdf:object> "a" . _:j0 <http://foo/b> "a" . <#BAG> <rdf:_2> _:j3 . _:j3 <rdf:type> <rdf:Statement> . _:j3 <rdf:subject> _:j0 . _:j3 <rdf:predicate> <http://foo/b> . _:j3 <rdf:object> "a" . A bag created by a BagID on a rdf:Description node with n property attributes has n! different graphs, on a typedNode this rises to (n+1)! different graphs. We can regard this as an issue in three different places: + either: (my preference) this is a bug with the XML/RDF syntax, solution: deprecate bagID when mixed with property attributes. + or (what M&S states) the unorderedness of a bag is fundamental, and the model theory must capture this despite the sequential numbering on its members. M&S ref http://lists.w3.org/Archives/Public/www-archive/2001Jun/att-0021/00-part#90 "Bags are used to declare that a property has multiple values and that there is no significance to the order in which the values are given" +or The radical position: M&S is simply wrong to show Bag membership with rdf:_NNN properties, if it is unordered make it a set not a bag and use rdf:li as the property! Jeremy
Received on Monday, 1 October 2001 13:40:32 UTC