The unification problem in first-order predicate calculus is described in general terms as the solution of a system of equations, and a nondeterministic algorithm is given. A new unification algorithm, characterized by having the acyclicity test efficiently embedded into it, is derived from the nondeterministic one, and a PASCAL implementation is given. A comparison with other well-known unification algorithms shows that the algorithm described here performs well in all cases.

. Object-Relational and Object-Oriented DBMSs allow users to invoke time-consuming ("expensive") methods in their queries. When queries containing these expensive methods are run on data with duplicate values, time is wasted redundantly computing methods on the same value. This problem has been studied in the context of programming languages, where "memoization" is the standard solution. In the database literature, sorting has been proposed to deal with this problem. We compare these approachesalong with a third solution, a variant of unary hybrid hashing which we call Hybrid Cache. We demonstrate that Hybrid Cache always dominates memoization, and significantly outperforms sorting in many instances. This provides new insights into the tradeoff between hashing and sorting for unary operations. Additionally, our Hybrid Cache algorithm includes some new optimizations for unary hybrid hashing, which can be used for other applications such as grouping and duplicate elimination. We conclude...

This paper advocates a programming methodology using message passing. Efficient programs are derived for fast exponentiation, merging ordered sequences, and path existence determination in a directed graph. The problems have been proposed by John Reynolds as interesting ones to investigate because they. illustrate significant issues in programming. The methodology advocated here is directed toward the production of programs that are intended to execute efficiently in a computing environment with many processors. The absence of the COTO construct does not seem to be constricting in any respect in the development of efficient programs using the programming methodology advocated here. The programming problems arising from use of the GOTO construct have become well known over the last decade. However, removal of the construct from traditional programming languages has been found by many to be constricting and to result in inefficient programs. A number of proposals have been advanced to allow the construct in a restricted way e.g. Knuth: 1974 and Reynolds: 19771.

Abstract not found