A. S. Lopatenko "Workshop on Exchange and Integration of Data" collocated with CASCON 2004, the 14th Annual IBM Centers for Advanced Studies Conference, IBM Toronto Lab http://www.scs.carleton.ca/~nvillanu/workshop.html , 10.2004 , language: английский  Аннотация The problem of query answering under exact views is considered. Our approach is based on Data Exchange settings: we describe an algorithm to create an incomplete table (in "c-tables" formalism by Imielnski) which describes all legal global databases. It is demonstrated that under EVA algebraic properties of a set of legal tables are signifantly different from algebraic properties of universal solution under SVA (what correlates with computational complexity and monotonicity results for query answering). By reduction of a query answering problem to constraint satisfaction problem (defined as a homomorphism problem) a few cases of tractable query answering are found.  Ключевые слова query answering, exact views, closed world, universal solution, data exchange, NP-hard, constraint satifaction problem