منابع مشابه
Conjunctive Query Containment Revisited
We consider the problems of conjunctive query containment and minimization, which are known to be NP-complete, and show that these problems can be solved in polynomial time for the class of acyclic queries. We then generalize the notion of acyclicity and deene a parameter called query width that captures the \degree of cyclicity" of a query: in particular, a query is acyclic if and only if its ...
متن کاملConjunctive Query Containment over Trees
The complexity of containment and satisfiability of conjunctive queries over finite, unranked, labeled trees is studied with respect to the axes Child , NextSibling , their transitive and reflexive closures, and Following . For the containment problem a trichotomy is presented, classifying the problems as in PTIME, coNP-complete, or Π 2 -complete. For the satisfiability problem most problems ar...
متن کاملConjunctive Query Containment under Access Limitations
Access limitations may occur when querying data sources over the web or heterogeneous data sources presented as relational tables: this happens, for instance, in Data Exchange and Integration, Data Warehousing, and Web Information Systems. Access limitations force certain attributes to be selected in order to access the tables. It is known that evaluating a conjunctive query under such access r...
متن کاملQuery Containment for Conjunctive Queries With
The management of semistructured data has recently received signiicant attention because of the need of several applications to model and query large volumes of irregular data. This paper considers the problem of query containment for a query language over semistructured data, StruQL0, that contains the essential feature common to all such languages, namely the ability to specify regular path e...
متن کاملConjunctive Query Evaluation by Search Tree Revisited
The most natural and perhaps most frequently used method for testing membership of an individual tuple in a conjunctive query is based on searching trees of partial solutions, or search-trees. We investigate the question of evaluating conjunctive queries with a time-bound guarantee that is measured as a function of the size of the optimal search-tree. We provide an algorithm that, given a datab...
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ژورنال
عنوان ژورنال: Theoretical Computer Science
سال: 2000
ISSN: 0304-3975
DOI: 10.1016/s0304-3975(99)00220-0