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Unformatted text preview: Getting All You Can Out of Views The situation is that we are given a collection of views and a query possibly recursive. 3 We want to nd all the answers to the query that we can using the views. This technology, due to Oliver Duschka, comes from Infomaster," a project of Prof. Mike Genesereth. Example We have a parent EDB relation, with ancestors de ned in the usual way: ancX,Y :- parX,Y ancX,Y :- parX,Z & ancZ,Y but the only view we have tells about grandparents: v1X,Y :- parX,Z & parZ,Y If we want the most ancestor facts that we can obtain from the view v1 not using the EDB, which is only abstract in applications like IM, then we should use the program: ancX,Y :- v1X,Y ancX,Y :- v1X,Z & ancZ,Y which gives us the even-distance ancestors that can be composed of facts in v1 , and nothing else. Key Idea: Skolemization 1. Replace existential variables in the view de nitions by new function symbols applied to the variables of the head. 3 The function symbols so used are called Skolem functions; it is a standard trick of lo...
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