Notethecase mancgistaken careofbyr8 29 exampler2andr3

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Unformatted text preview: ction­symbol pattern. 2. Replace EDB predicates (m and f in our example) by their definition in terms of views, but only if no function symbols are introduced. 26 Justification for (2) x A function symbol in a view is useless, since the source (stored) data has no tuples with function symbols. x A function symbol in an IDB predicate has already been taken care of by expanding the rules using all function­ symbol patterns we can construct. 27 New IDB Predicates x In our example, we only need manc1 to represent the pattern manc(g(.,.),.). x That is: manc1(X,Y,Z) = manc(g(X,Y),Z). 28 Example ­­­ r1 r1: manc(X,Y) :- m(X,Y) r5: m(g(X,Y),Y) :- v1(X,Y) r6: m(X,Y) :- v2(X,Y) Substitution OK; yields manc(X,Y) :- v2(X,Y) Illegal ­­­ yields g in head. Note the case manc(g(.,.),.) is taken care of by r8. 29 Example ­­­ r2 and r3 r2: manc(X,Y) :- f(X,Z) & manc(Z,Y) r3: manc(X,Y) :- m(X,Z) & manc(Z,Y) r4: f(X,g(X,Y)) :- v1(X,Y) r5: m(g(X,Y),Y) :- v1(X,Y) r6: m(X,Y) :- v2(X,Y) Illegal ­­­ put function symbol g in manc. OK; yields manc(X,Y) :- v2(X,Z) & manc(Z,Y) 30 Example ­­­ r4, r5, r6 x The inverse rules have played their role and do not appear in the final rules. 31 Example ­­­ r7 r7: manc(X,Y) :- f(X,g(B,C)) & manc(g(B,C),Y) r4: f(X,g(X,Y)) :- v1(X,Y) Unify. Note no function symbols are introduced, but X =B. Replace by manc1(B,C,Y). r7: manc(X,Y) :- v1(X,C) & manc1(X,C,Y) 32 Example ­­­ r8 and r9 r8: manc(g(A,B),Y) :- m(g(A,B),Y) r9:manc(g(A,B),Y) :- m(g(A,B...
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This document was uploaded on 01/06/2012.

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