ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, p...
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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Many widely used file organizations can be logically divided into 2 comp.nents: the index comp.nent and the data leaves comp.nent. File records are maintained in data leaves; each leaf is a logical unit stored in con...
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Many widely used file organizations can be logically divided into 2 comp.nents: the index comp.nent and the data leaves comp.nent. File records are maintained in data leaves; each leaf is a logical unit stored in contiguous disk pages. The index comp.nent is a search structure used to search for the appropriate data leaf. An efficient method for reducing the index size involves the use of multibucket leaves. Because of an anomalous behavior of the hash function, some primary buckets may be overloaded, while other primary buckets of the same multibucket leaf are not loaded. The performance of file organizations that use multibucket leaves is analyzed under a sequence of insert operations. It is shown that, when the number of primary buckets per leaf increases, the average disk space utilization decreases. This reduction in the average disk space utilization is more moderate when the bucket size increases.
This paper is concerned with the design of sound and comp.ete proof systems for programming languages. Proof systems are designed to verify correctness of programs by means of formal deductions. A proof system is an a...
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This paper is concerned with the design of sound and comp.ete proof systems for programming languages. Proof systems are designed to verify correctness of programs by means of formal deductions. A proof system is an axiomatic system in which properties of programs, expressed as logical formulae, can deduced formally. A comp.sitional proof system is a syntax-directed proof system in which properties of programs are proved using the properties of their syntactic subprograms.
MINIMUM COVER is a typical problem of an important class of combinatorial problems that consists of set covering and partitional problems. Many of these problems are NP-comp.ete. In an inst.nce of MINIMUM COVER, the...
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MINIMUM COVER is a typical problem of an important class of combinatorial problems that consists of set covering and partitional problems. Many of these problems are NP-comp.ete. In an inst.nce of MINIMUM COVER, the subsets of S are listed, and S itself is implicitly represented as the union of these subsets. In the problems presented, the representation of the inst.nce is in some sense the reverse. The inst.nce is a collection C of subsets of a finite set S, positive integer K less than or equal to set C. It is to be determined whether C contains a cover for S the size of K or less. Since the problems illustrated have not been shown to be NP-comp.ete in the strong sense, there is hope for a pseudopolynomial time algorithm for each problem. If set S is equal to n and Z is restricted to only those arithmetic progressions having a fixed increment m, then a minimum cover is found from Z in O(n log n) time.
An algorithm is presented for evaluating joins in distributed relational databases. The cost of evaluating the join is typically lower than that of using the semi-join algorithm. The resultant join, however, is hori...
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An algorithm is presented for evaluating joins in distributed relational databases. The cost of evaluating the join is typically lower than that of using the semi-join algorithm. The resultant join, however, is horizontally partitioned. The algorithm is comp.red with the semi-join algorithm and is demonstrated to furnish good performance in circumstances where the semi-join is not appropriate. Examples of situations in which this technique can be useful are given. If information is required about the size of the join, rather than its contents, the main cost is the calculation of the join, rather than its communication. In this case, a savings results by using the distributed join. If the join of several relations is required, the associated query may be cyclic, in which case calculating semi-joins may not help. However, it is possible to reduce the cost using distributed joins.
Resource constrained scheduling is an area of operations research in which the availability of high resolution graphics hardware and software increases the demand for visual interactive modeling tools. Most practical...
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Resource constrained scheduling is an area of operations research in which the availability of high resolution graphics hardware and software increases the demand for visual interactive modeling tools. Most practical resource constrained problems belong to the NP-comp.ete class, so their solutions are usually sought using heuristic techniques. A discussion of ideas related to the object-oriented graphical representation of resource constrained schedules highlights the apparent link between resource constrained scheduling and 2-dimensional bin-packing theory. Two graph theoretical problems are formulated and shown to be useful when constructing a graphical representation for a schedule. The 2 graph theoretical problems are interval chromatic number and graph acyclic orientability with weighted diameter K.
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