47450428
An Algorithm to Compact a VLSI Symbolic Layout with Mixed Constraints
A popular algorithm to compact VLSI symbolic layout is to use a graph algorithm similar to finding the "longest path" in a network. The algorithm assumes that the spacing constraints on the mask elements are of the lower bound type. However, to enable the user to have close control over the compaction result, a desired symbolic layout system should allow the user to add either the equality or the upper bound constraints on selected pairs of mask elements as well. This paper proposes an algorithm which uses a graph-theoretic approach to solve efficiently the compaction problem with mixed constraints.
8508688
New algorithms for the rectilinear Steiner tree problem
An approach to constructing the rectilinear Steiner tree (RST) of a given set of points in the plane, starting from a minimum spanning tree (MST), is discussed. The main idea in this approach is to find layouts for the edges of the MST that maximize the overlaps between the layouts, thus minimizing the cost (i.e. wire length) of the resulting rectilinear Steiner tree. Two algorithms for constructing rectilinear Steiner trees from MSTs, which are optimal under the conditions that the layout of each edge of the MST is an L shape or any staircase, respectively, are described. The first algorithm has linear time complexity and the second algorithm has a higher polynomial time complexity. Steiner trees produced by the second algorithm have a property called stability, which allows the rerouting of any segment of the tree, while maintaining the cost of the tree, and without causing overlaps with the rest of the tree. Stability is a desirable property in VLSI global routing applications. >
15727543
Securing Mobile Agents for Electronic Commerce: An Experiment
Mobile software agents are becoming a major trend of distributed systems in the next decade. Electronic commerce and information retrieval are two prospective applications of mobile agents. Nevertheless, security is a crucial concern for such systems. Attacks to agents by malicious hosts are the most challenging part of the problem unsolved. In this paper, a Shopping Information Agent System (SIAS) is built based on mobile agent technology. Possible security attacks by malicious hosts to agents in the system are discussed, and solutions to prevent these attacks are presented. Security of the solutions is analysed, and the performance overhead introduced is evaluated.
16381803
Upper and lower bounds for graph-diameter problems with application to record allocation
This paper studies three graph problems with parameters n, the number of nodes, e, the number of edges, and k, the diameter of the graph. Given any two of these three parameters, the problem is to construct a directed graph which minimizes or maximizes the third. The first problem has its origin in a recent study of record allocation in a paged computer system. It is shown how to construct graphs that are optimal for all three problems in some cases and are asymptotically optimal for other cases. The solution of the second problem answers a question raised by Berge in “The Theory of Graphs and its Application,” 1962.
7180182
Minimizing mean flow time with error constraint
In a new model of task systems studied by J.W.S. Liu et al. (1987) each task is logically decomposed into two subtasks, mandatory and optional. The authors discuss preemptively scheduling this kind of task system on p>or=1 identical processors so as to minimize the mean flow time. Given a task system and an error threshold K, the goal is to find a preemptive schedule such that each task is executed in the interval of its release time and deadline, the average error is no more than K, and the mean flow time of the schedule is minimized. Such a schedule is called an optimal schedule. It is shown that the problem of finding an optimal schedule is NP-hard for each p>or=1, even if all tasks have the same ready time and deadline. For a single processor, a pseudo-polynomial time algorithm and polynomial time algorithms for various special cases of the problem are given.<<ETX>>
1310783
Design, Implementation, and Experimentation on Mobile Agent Security for Electronic Commerce Applications
In this paper, a Shopping Information Agent System (SIAS) is built based on mobile agent technology. It sends out agents to di erent hosts in an electronic marketplace. The agents collect and report information such as prices and availabilities about products speci ed by users. Snapshots of the system in use are shown. Security is a major problem of mobile agent systems, especially when money transactions are concerned. Possible security attacks by malicious hosts to agents in SIAS are discussed, and a solution to prevent these attacks is presented. Finally, security of the solution is analyzed, and the performance overhead introduced is
34486647
Minimum Fill-In on Circle and Circular-Arc Graphs
We present two algorithms solving the minimum fill-in problem on circle graphs and on circular-arc graphs in time O(n3).