Showing papers by "Richard Cole published in 1998"

On Balls and Bins with Deletions

Abstract: We consider the problem of extending the analysis of balls and bins processes where a ball is placed in the least loaded of d randomly chosen bins to cover deletions. In particular, we are interested in the case where the system maintains a fixed load, and deletions are determined by an adversary before the process begins. We show that with high probability the load in any bin is O(log log n). In fact, this result follows from recent work by Cole et al. concerning a more difficult problem of routing in a butterfly network. The main contribution of this paper is to give a different proof of this bound, which follows the lines of the analysis of Azar, Broder, Karlin, and Upfal for the corresponding static load balancing problem. We also give a specialized (and hence simpler) version of the argument from the paper by Cole et al. for the balls and bins scenario. Finally, we provide an alternative analysis also based on the approach of Azar, Broder, Karlin, and Upfal for the special case where items are deleted according to their age. Although this analysis does not yield better bounds than our argument for the general case, it is interesting because it utilizes a two-dimensional family of random variables in order to account for the age of the items. This technique may be of more general use.

Randomized protocols for low-congestion circuit routing in multistage interconnection networks

Abstract: In this paper we study randomized algorithms for circuit switching on multistage networks related to the butterfly. We devise algorithms that route messages by constructing circuits (or paths) for the messages with small congestion, dilation, and setup time. Our algorithms are based on the idea of having each message choose a route from two possibilities, a technique that has previously proven successful in simpler load balancing settings. As an application of our techniques, we propose a novel design for a data server.

Approximate string matching: a simpler faster algorithm

Abstract: We give two algorithms for finding all approximate matches of a pattern in a text, where the edit distance between the pattern and the matching text substring is at most k The first algorithm, which is quite simple, runs in time O( nk 3 m + n + m) on all patterns except k-break periodic strings (defined later) The second algorithm runs in time O( nk 4 m + n + m )o nk-break periodic patterns The two classes of patterns are easily distinguished in O(m) time

Constructing conceptual scales in formal concept analysis

Abstract: Formal concept analysis (FCA) is a technique for knowledge visualisation. Several software tools have been developed to aid knowledge exploration using FCA, the most prevelant of these being TOSCANA. This paper describes a tool to allow the creation of conceptual scales by a domain expert. The tool employs techniques of direct manipulation to provide the user with an intuitive understanding of FCA. Examples from a case study employing Medical Subject Headings (MeSH) and a set of medical texts.