- From: Stefan Kokkelink <skokkeli@mathematik.uni-osnabrueck.de>
- Date: Mon, 03 Sep 2001 10:24:42 +0200
- To: pat hayes <phayes@ai.uwf.edu>
- CC: www-rdf-logic@w3.org
pat hayes wrote: > ... > >Although I completely agree on this (and on the decisions > >made by RDFCore regarding anonymous nodes and RDF graphs ) > >it should be noted that there is no 1:1 correspondence between > >XML serializations and RDF graphs (and hence Ntriple also). > > But it is onto, ie every XML serialization maps to a unique graph, > right? onto? which mapping do you mean? The mapping XML -- parse --> RDF-Graphs is neither injective nor surjective. It is not injective because parse(<Description dc:title="a"/>) equals parse(<Description><dc:title>a</dc:title></Description>) It is not surjective, because there is no XML serialization for <URI1> <PROP1> _:a. <URI2> <PROP2> _:a. The parse function may be used to define a an equivalence relation ~ on XML by a~b <=> parse(a)=parse(b). Let XML-Ser denote the set XML/~ . Then the mapping XML-Ser >--> RDF graphs is injective. > (If not, please give an example.) So if the semantics assigns > a meaning to every graph, then it also does to every XML > serialization, which is all that it needs to do in order to provide a > semantics for the serialization language. Yes. > >I think there are two possible views on this. > > > >1. Accept that not all RDF graphs have a XML serialization. > > That would be my own preference. Is there a problem with this? This could be a problem for developers. For example if you use an API like Jena for creating RDF graphs, it may be not possible to serialize the created graphs. > >2. Define an RDF graph to be a 'valid' RDF graph if there > > exist a XML serialization. > > Well, I'd prefer a different word, call it 'XML-compliant' or some > such. But this is a different issue, to do with the acceptability of > RDF graphs to some processor. The model theory only has to provide an > unambiguous interpretation for every expression; if it also provides > one for some other expressions that is harmless. Yes, this is no problem for the model theory. I just wanted to point out that the decisions concerning anonymous resources have some (possibly non-harmless) effects on the mappings between graphs, XML, model ... Currently, we have: XML-Ser >--> RDF Graphs >-->> N-Triple Regards, Stefan
Received on Monday, 3 September 2001 04:25:24 UTC