Abel2007enabling presented by Tim Lebo 25 sept 2008 Gregory Todd Williams 1

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• Question is for the Presentation: Abel2007enabling presented by Tim Lebo 25 sept 2008
• Question is asked by: Gregory Todd Williams
• The Question is: ONE: Section 1 states that evaluating complex conditions "for each triple to be potentially returned by the metadata store is not affordable, since it is too expensive in terms of time." Ignoring the context-dependent parts of a policy (which can be verified before query execution as in the presented system), this seems to be essentially exactly what the proposed system does by adding new expressions to the query. TWO: Understanding that it would make for a "repository-dependent and not portable" solution, would there be efficiency benefits to performing these conditions at the triple store level where a clear distinction could be made between the query pattern and the policy conditions?

Response: ONE: When additional expressions are added to the incoming query, the off-the-shelf repository has more "metadata" constraints (as opposed to contextual constraints) that it can use to guide search planning. When these additional constraints are used, inappropriate triples are omitted without evaluation. This is how constraints are not evaluated for all "triples that are potentially returned." TWO: I don't see any efficiency benefits to distinguishing between the query patterns and the policy conditions. Is there something about the structure of the "expanded" query that existing triple stores are not optimized for?warning.pngString representation ONE: When additional expressions are added […] sting triple stores are not optimized for? is too long.