Query Order and NP-Completeness
نویسندگان
چکیده
The e ect of query order on NP completeness is investigated A sequence D D Dk of decision problems is de ned to be sequentially complete for NP if each Di NP and every problem in NP can be decided in polynomial time with one query to each of D Dk in this order It is shown that if NP contains a language that is p generic in the sense of Ambos Spies Fleischhack and Huwig then for every integer k there is a sequence D D Dk such that D is sequentially complete for NP but no nontrivial permutation Di Dik of D is sequentially complete for NP It follows that such a sequence D exists if there is any strongly positive p computable probability measure such that p NP
منابع مشابه
Query Order and NP - Completeness 1
The eeect of query order on NP-completeness is investigated. A sequence ~ D = (D 1 ; : : : ; D k) of decision problems is deened to be sequentially complete for NP if each D i 2 NP and every problem in NP can be decided in polynomial time with one query to each of D 1 ; : : : ; D k in this order. It is shown that, if NP contains a language that is p-generic in the sense of Ambos-Spies, Fleischh...
متن کاملExpressiveness and Complexity of Order Dependencies
Dependencies play an important role in databases. We study order dependencies (ODs)—and unidirectional order dependencies (UODs), a proper sub-class of ODs—which describe the relationships among lexicographical orderings of sets of tuples. We consider lexicographical ordering, as by the order-by operator in SQL, because this is the notion of order used in SQL and within query optimization. Our ...
متن کاملA -Query Non-Adaptive PCP with Perfect Completeness
We study a very basic open problem regarding the PCP characterization of NP, namely, the power of PCPs with non-adaptive queries and perfect completeness. Optimal results are known if one sacrifices either non-adaptiveness or perfect completeness. Håstad [11] constructs a -query non-adaptive PCP with soundness but it loses prefect completeness ( is an arbitrarily small constant). Guruswami et a...
متن کاملComputing Possible and Certain Answers over Order-Incomplete Data
This paper studies the complexity of query evaluation for databases whose relations are partially ordered; the problem commonly arises when combining ordered data from multiple sources. We focus on queries in a useful fragment of SQL, namely positive relational algebra with aggregates, whose bag semantics we extend to the partially ordered setting. Our semantics leads to the study of two main c...
متن کاملPossible and Certain Answers for Queries over Order-Incomplete Data
To combine and query ordered data from multiple sources, one needs to handle uncertainty about the possible orderings. Examples of such “order-incomplete” data include integrated event sequences such as log entries; lists of properties (e.g., hotels and restaurants) ranked by an unknown function reflecting relevance or customer ratings; and documents edited concurrently with an uncertain order ...
متن کامل