Abel2007enabling presented by Tim Lebo 25 sept 2008 Shangguan 3

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• Question is for the Presentation: Abel2007enabling presented by Tim Lebo 25 sept 2008
• Question is asked by: Zhenning Shangguan
• The Question is: ONE: About DEFINITION_2 in section 4.3. The author only stated that σ and σ (double prime) might exist. Suppose that they do exist, how can we get it? TWO: Another thing that confused me a lot is the example of the returned value after applying pol1_pol4 onto some sample RDF triples, in which Var1-Var9 are not clearly defined. I can understand that this is only an example, so some information fragments might get lost due to space considerations. But, we come back to the example of expanded RDF query in Section 5, things become confusing again --the Var's in this example are still not defined. So, how do we handle this problem?

About DEFINITION_2 in section 4.3. The author only stated that σ and σ might exist. Suppose that they do exist, how can we get it? Another thing that confused me a lot is the example of the returned value after applying pol1_pol4 onto some sample RDF triples, in which Var1-Var9 are not clearly defined. I can understand that this is only an example, so some information fragments might get lost due to space considerations. But, we come back to the example of expanded RDF query in Section 5, things become confusing again --the Var's in this example are still not defined. So, how do we handle this problem?

ONE: It is not that σ and σ (double prime) /might/ exist; it is that they /must/ exist in order for the policy to apply to the path expression. σ and σ (double prime) are unifiers (set of map pairings) that replace terms in their operand, whether the operand be another unifier or a path expression. The σ (double prime) is the unifier resulting from the disunification of each path expression, the σ' (prime) is the most general unifer, and σ is the unifier that brings all of the terms for ALL expressions into the "common term naming space". TWO: Var1-Var9 are "fresh variables" that are minted during the disunification of DEFINITION_1. These new variables replace the original subject and object in the path expression, and the identity is preserved with the mapping (σ) that is added to \theta. For an introduction to unification, see of http://www.cs.sfu.ca/CC/SW/Prolog/Notes/unif.html the algorithm you are looking for is in section 2.1.warning.pngString representation ONE: It is not that σ and σ (double prim […] thm you are looking for is in section 2.1. is too long.