This preview shows page 1. Sign up to view the full content.
Unformatted text preview: X,Y Evaluating the Rules
In a sense, that's all there is to it. Treat all
predicates except the views as IDB, and evaluate.
Seminaive evaluation can produce tuples with
function symbols, but these cannot be real
answers to the query.
Because all function symbols are in the heads
of rules for EDB" global, conceptual
predicates, which have no other rules, we
never introduce a function symbol within a
function symbol, leading to a nite process.
Thus, seminaive evaluation converges, and the
set of manc facts without function symbols is
the closest we can get to the true answer by
using only the views.
2 Example of Inference
Suppose v1 a; b. Then we can infer:
mga; b; b by r5 .
mancga; b; b by r1.
f a; ga; b by r4.
manca; b by r2 . Formal Elimination of Function Symbols
If you feel uncomfortable with function symbols
oating around, there is a systematic way to
rewrite the rules so there are no function symbols
at all.
Create new versions of the rules by using any
pattern with function symbols that appears
in a head, and using...
View
Full
Document
 Spring '09

Click to edit the document details