- From: Seaborne, Andy <andy.seaborne@hp.com>
- Date: Mon, 21 Mar 2005 16:04:29 +0000
- To: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Matters arising from the comments list: 1/ SELECT to involve expressions SQL allows constants and expressions in explicit projections (SQL SELECT in other words) SELECT ?x "constant" ... SELECT ?x (?x+?y) ... Combined with nested SELECTs and UNIONs, we would have a way to tag which branch of a union a solution came from. This can already be done using different variables in each branch. This would require access to results by column number (or aliases which are not required by SQL) and so have impact on the results format. At the moment, SPARQL UNION is defined without the explicit SELECT projection and is a graph pattern operator. There is no no assignment of values - it's not possible to return RDF terms that are not in the graph or a dataset label. 2/ GROUP BY Request for SQL-like GROUP BY in addition to ORDER BY. GROUP BY allows the application of aggrgeate functions which is more problematic than ORDER BY (that only chnages the order of solutions, it does not remove, add or change solutions). It's use with aggregation functions like sum(), count() that is tricky because of defining what is being counted (names or individuals). COUNT() can lead to a significant decrease in network bandwidth but I have not seen a proposal as to what it means for RDF query that explciitly addresses the closed world assumptions. Andy
Received on Monday, 21 March 2005 16:22:59 UTC