- From: Andy Seaborne <andy.seaborne@talis.com>
- Date: Tue, 16 Mar 2010 09:59:51 +0000
- To: Lee Feigenbaum <lee@thefigtrees.net>
- CC: SPARQL Working Group <public-rdf-dawg@w3.org>
These are the issues in the document: * The use of "^" as a unary and binary operator may be confusing. In the N3 community "^" is binary (and you can't say ":x ^foaf:knows :y"). In N3, things are more resource-centric and you can write paths in the subject and object locations of a "triple". The property path design is arc-centric. The WG tends towards "^" being unary and having to write "/^". I think we should not invalidate the N3 style completely when it is just a matter of syntax. This is only about syntax. It does not change the operators. * While property paths as currently specified can be used to access RDF lists (e.g. rdf:rest*/rdf:first), the Working Group notes that this would be more useful if results were returned in the order they occur in the RDF list. This presents significant complexity in the context of the existing SPARQL algebra. I don't think there is anything we can do about this. It would be a much wider change to SPARQL, roughly, for every algebra operator, say what its effect on ordering is, but that is not a change to SPARQL 1.0 because the order can't be set except by ORDER BY and that's at the top level of a SPARQL1.0 query. See also ORDER BY in sub-SELECTs in SPARQL 1.1 * The WG has discussed providing access to the length of matched paths, which would provide greater functionality but would complicate path evaluation. At this time, the WG's primary aim is to specify a core set of functionality while not blocking future enhancements. Currently, we aren't considering explicit lengths. No time. * How does this interact with inference when SPARQL is used with systems carrying out inference as part of query processing? Proposal (RDFS, RIF?): it's equivalent to walking the virtual triples. I don't know about OWL, DL or Direct. * Paths expressions match once even if there are multiple possible paths between two points (c.f. SPARQL BGP) ((Discussed in other email.)) Andy
Received on Tuesday, 16 March 2010 10:00:22 UTC