Showing papers on "Graph database published in 1980"

Variations on the Common Subexpression Problem

Abstract: Let G be a directed graph such that for each vertex v in G, the successors of v are ordered Let C be any equivalence relation on the vertices of G. The congruence closure C* of C is the finest equivalence relation containing C and such that any two vertices having corresponding successors equivalent under C* are themselves equivalent under C* Efficient algorithms are described for computing congruence closures in the general case and in the following two special cases. 0) G under C* is acyclic, and (it) G is acychc and C identifies a single pair of vertices. The use of these algorithms to test expression eqmvalence (a problem central to program verification) and to test losslessness of joins in relational databases is described

Modelling concepts for reasoning about access to knowledge

Abstract: There is growing agreement about the usefulness of putting semantic database constraints into explicit form that can be manipulated by various database management programs. Indeed, this is a prerequisite for building intelligent database mediators. These are programs that perform the task of a good database analyst: to pose the most effective and easily processed queries to help solve a problem. Semantic query optimization is a technique to exploit semantic constraints for one aspect of intelligent database mediation: increasing retrieval efficiency. The technique is to use semantic constraints to transform a query into an equivalent one that can be processed more efficiently. Various kinds of semantic knowledge that can be used for this purpose are described.

Graph Algorithms for the Synthesis and Manipulation of Data Base Schemes

Abstract: In this paper the graph formalism for the representation of relational data base schemes is presented.