Feature: Control of Describe Queries

Feature description

Currently it is left undefined as to how a SPARQL processor should generate the results of a DESCRIBE query. There are several possible algorithms that might be applied, and these are useful in different contexts. It would be useful to be able to specify an algorithm in the SPARQL query, so that the client has additional control over the form of the results.

Algorithms would be referred to be URI. The specification may define zero or more of these, and implementations might converge on a standard set.

Example

I'd envisage something like:

DESCRIBE ?x WHERE {
  ?x a foaf:Person.
}
USING <http://www.example.org/closure/concise-bounded-desc>

...where USING refers to a standard URI for the algorithm used to describe the results.

Existing Implementation(s)

Virtuso has a similar feature using query pragmas, e.g. define sql:describe-mode "SPO"

Existing Specification / Documentation

Compatibility

Links to postponed Issues

Old Email threads: http://lists.w3.org/Archives/Public/public-rdf-dawg/2006JanMar/0521.html

Issue: http://www.w3.org/2001/sw/DataAccess/issues#DESCRIBE

Related Features

Feature:DefaultDescribeResult about creating a default result algorithm.

Champions

submitted via public-rdf-dawg-comments@w3.org by Leigh Dodds, Programme Manager, Talis, cf. http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2009Mar/0029.html

Use Cases

Provide more control over form of DESCRIBE query results on the client. It is not always possible to achieve the same effect with a CONSTRUCT query due to other limitations in the language (e.g. in graph traversal, container construction, etc). Even if those issues were resolved there are advantages in the coarse grain style of query that this feature provides.

References