Finding Compact Scheme Forests
نویسندگان
چکیده
In traditional relational databases, the data is stored in \ at" tables. Query processing performance is dominated by the cost of joining such tables. By contrast, nested relational structures can avoid joins. If, however, such structures are decomposed into nested normal form (NNF) then the number of normal scheme trees in the resulting nested scheme forest may dominate query processing performance. Thus minimizing the number of such trees is an important design goal. We prove that the problem of nding a succinct NNF scheme forest is NP-hard even for the class of sets of unary multivalued dependencies, which is a subclass of the class of split-free sets of multivalued dependencies. 3 List of Symbols Used S set theory union T set theory intersection 2 set theory \element of" set theory proper subset set theory subset Greek upper-case Gamma Greek upper-case Phi Greek lower-case pi Greek upper-case Psi Greek upper-case Theta P Boldface P R Boldface R E \calligraphic" E G \calligraphic" G T \calligraphic" T !! double arrow ./ bow tie 4
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