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Generalized Containment of Conjunctive Queries

出版	University of Wisconsin-Madison, Computer Sciences Department, 1992
URL	http://books.google.com.hk/books?id=UxxiPgAACAAJ&hl=&source=gbs_api

註釋Abstract: "Conjunctive queries are queries over a relational database, and are composed of the relational algebra operators select, project and cartesian product. In this paper, we study conjunctive queries over databases in which each tuple has an associated label; as a special case, in a traditional relational database, the label associated with a tuple is either 1 (meaning that that tuple is 'in' the relation) or 0 (meaning that the tuple is not in the relation). In particular, this generalized notion of a database allows us to consider relations that are fuzzy sets or multisets. Conjunctive queries over a relational database can be viewed as functions from sets to sets and containment (equivalence) can be naturally defined based on set inclusion.