Tohru Kikuno

A linear algorithm for the domination number of a series-parallel graph

Abstract A vertex u in an undirected graph G = (V, E) is said to dominate all its adjacent vertices and itself. A subset D of V is a dominating set in G if every vertex in G is dominated by a vertex in D, and is a minimum dominating set in G if no other dominating set in G has fewer vertices than D. The domination number of G is the cardinality of a minimum dominating set in G. The problem of determining, for a given positive integer k and an undirected graph G, whether G has a dominating set D in G satisfying ¦D¦ ≤ k, is a well-known NP-complete problem. Cockayne have presented a linear time algorithm for finding a minimum dominating set in a tree. In this paper, we will present a linear time algorithm for finding a minimum dominating set in a series-parallel graph.

A semantic approach to usability in relational database systems

This paper attempts to design a user-friendly interface which enhances usability of relational database systems. Our approach to usability is to design a semantic data model suitable for a user interface and provide an easy-to-use query language DOMCALC (domain calculus language) which is based on the semantic data model. A query in DOMCALC can be described in terms of intuitive notions, namely domains, instead of relations and attributes. That is, DOMCALC requires for users no knowledge of a conceptual database such as relation names and attribute names. Therefore, the usability based on the semantic data model removes the requirement of knowledge of a conceptual database from users and protects user views from changes in the conceptual database. We also describe an outline of a database system PRIM (Prototype of Laboratory information Management System) which has been developed with the above considerations. This is a step toward the enhancement of usability in relational database systems.

A Visual Language for Forms Definition and Manipulation

An office information system plays a key role in office automation. The most important factor in the office information system is a user-friendly interface, since office workers may be novices for computers. Forms provide a uniform and comfortable interface with the office workers, since much information within an office is found in forms such as reports, letters, and memorandums. Therefore, office information systems should be based on electronic forms which are the computer analog of paper forms.

Design of hardware algorithms by recurrence relations

With the progress in VLSI technology, a remarkable attempt, called the hardware algorithm, to realize various kinds of algorithms directly as hardware on VLSI chip has become practical. No significant result, however, has been observed on the systematic formulation of the hardware algorithm or its design method. This paper proposes a new design method for the hardware algorithm using recurrence relations. As the first step, a class C of problems is introduced which is defined by the recurrence relations with two variables. Several practically important problems such as string matching, are contained in this class. It is shown that letting the size of the problem be m, one can always construct a hardware algorithm of 0(m) steps to solve any problem in the class C. Then by imposing a certain restriction on the recurrence relation, a subclass C1 of the class C is defined. It is shown that the hardware algorithm of 0 (log m + m/log m) steps can be constructed for the subclass C1. Finally, the extension of the class C is discussed, and it is shown that its algorithm can be applied, with some modifications, to a class of recurrence relations which is wider than the class C.

Response time minimization for processing simple queries in star networks

It has already been shown that the problem of obtaining an optimal strategy for a general query on a distributed database system is NP-hard. On the other hand, simple queries have been known as one class of queries for which an optimal strategy can be obtained efficiently. So far, it has been shown that if the topology of a computer network is a complete graph, then a strategy with the minimum response time for simple queries can be obtained in O(n2), where n is the number of sites of the network. This paper discusses the problem of obtaining a strategy with the minimum response time for simple queries when the topology of a computer network is a star (in brief, problem RT). We assume that each communication channel of a star network has equal communication capacity, and that each site has an equal capability for data processing. Here, we also assume that the center of a star network is capable of performing so-called broadcasting. In this paper, we present an algorithm called RT of O(n2) time for solving problem RT. Algorithm RT constructs a schedule graph that represents an optimal strategy by using the dynamic programming method.

NP-completeness of some type of p-center problem

Abstract In this paper we will define some special p -center problem in view of practical applications and prove its NP-completeness.

Optimization of Multiple Queries in Relational Database Systems

Recently, relational database systems which allow concurrent executions have been developed on mainframes and minicomputers. In such a system, optimization of multiple queries can be performed as an extension of optimization of a single query. By unifying the common operations in the multiple queries, the computation time or the number of disk page fetches can be reduced. In this paper, the optimization of the join operations is considered, since the join operation is the most time-consuming one in the relational database. A problem (problem JM) is formulated to minimize the number of disk page fetches by unifying the common join operations in multiple queries. The number of page fetches depends on the realization method of a single join operation. In this paper, it is assumed that the join operation follows the nested loops method [4]. This paper proposes a heuristic algorithm for problem JM, and the effectiveness of the method is evaluated by a simulation experiment.

Feasibility problem for meeting timetable rearrangement

Scheduling of meetings is one of the basic functions demanded in office automation. With respect to the automation of this function, the Meeting Timetable Rearrangement problem (MTR) to update a current meeting timetable for an additional meeting has been formulated. However, it has already been shown that MTR is NP-hard. Consequently, we should develop an approximation algorithm or a heuristic algorithm for MTR. Such an algorithm is required to find a feasible solution which satisfies all constraints, but not necessarily an optimal solution. This paper discusses a problem to determine whether or not there exists a feasible solution for a given instance of MTR. First, we show that this problem is NP-complete. That is, there is no polynomial-time approximation algorithm for MTR unless P = NP. This implies that we should develop a heuristic algorithm for MTR. Second, we present a polynomial-time algorithm which finds a feasible solution for a subproblem of MTR. By combining this algorithm and a hill-climbing approach, an efficient heuristic algorithm can be developed.

Design of an Easy-to-Use Query Language for Office Automation

The increasing extent to which applications of computer systems have been applied has made the design of a user-friendly interface a more critical problem in the development of computer systems. In particular, a database system for office automation must provide a query language that allows users without any skill to access data.