Abstract Mining association rules in relational databases is a significant computational task with lots of applications. A fundamental ingredient of this task is the discovery of sets of attributes (itemsets) whose frequency in the data exceeds some threshold value. In this paper we describe two algorithms for completing the calculation of frequent sets using a tree structure for storing partial supports, called interim‐support (IS) tree. The first of our algorithms (T‐Tree‐First (TTF)) uses a novel tree pruning technique, based on the notion of (fixed‐prefix) potential inclusion, which is specially designed for trees that are implemented using only two pointers per node. This allows to implement the IS tree in a space‐efficient manner. The second algorithm (P‐Tree‐First (PTF)) explores the idea of storing the frequent itemsets in a second tree structure, called the total support tree (T‐tree); the main innovation lies in the use of multiple pointers per node, which provides rapid access to the nodes of the T‐tree and makes it possible to design a new, usually faster, method for updating them. Experimental comparison shows that these techniques result in considerable speedup for both algorithms compared with earlier approaches that also use IS trees (Principles of Data Mining and Knowledge Discovery, Proceedings of the 5th European Conference, PKDD, 2001, Freiburg, September 2001 (Lecture Notes in Artificial Intelligence, vol. 2168). Springer: Berlin, Heidelberg, 54–66; Journal of Knowledge‐Based Syst. 2000; 13:141–149). Further comparison between the two new algorithms, shows that the PTF is generally faster on instances with a large number of frequent itemsets, provided that they are relatively short, whereas TTF is more appropriate whenever there exist few or quite long frequent itemsets; in addition, TTF behaves well on instances in which the densities of the items of the database have a high variance. Copyright © 2008 John Wiley & Sons, Ltd.

In this paper we examine the effect that the choice of support and confidence thresholds has on the accuracy of classifiers obtained by classification association rule mining. We show that accuracy can almost always be improved by a suitable choice of threshold values, and we describe a method for finding the best values. We present results that demonstrate this approach can obtain higher accuracy without the need for coverage analysis of the training data.

In this paper a number of classification rule evaluation measures are considered. In particular the authors review the use of a variety of selection techniques used to order classification rules contained in a classifier, and a number of mechanisms used to classify unseen data. The authors demonstrate that rule ordering founded on the size of antecedent works well given certain conditions.

Two new structures for association rule mining (ARM), the T-tree, and the P-tree, together with associated algorithms, are described. The authors demonstrate that the structures and algorithms offer significant advantages in terms of storage and execution time.

We consider a technique (DATA-VP) for distributed (and parallel) association rule mining that makes use of a vertical partitioning technique to distribute the input data, amongst processors. The proposed vertical partitioning is facilitated by a novel compressed set enumeration tree data structure (the T-tree), and an associated mining algorithm (Apriori-T), that allows for computationally effective distributed/parallel ARM when compared with existing approaches.

Current developments in browser technology have largely ignored academic research on interface design in hypermedia systems. This is unlikely to change in the future. Thus, the needs of an information society must be met by providing appropriate training in the use of the technology in the community. To be effective, such training has to identify the difficulties computer-naive members of the public experience with existing systems and to consider both software and training based solutions to these problems. This paper seeks to encourage debate about strategies for facilitating access to Internet technology in the community by reviewing both the success and the difficulties encountered in a public access to the Internet outreach programme, the Internet Express, currently operating at libraries in Merseyside, UK.

Archives of software packages made available on the Internet have become an increasingly common and important way of distributing these resources. To improve local access speeds, it is common for these archives to be mirrored, i.e. replicated at regional sites throughout the world. When these sites are also active participants in the augmentation and maintenance of the archive, it becomes necessary to impose a regime which will ensure that errors and inconsistencies do not arise as a result of conflicting activities at different centres. We describe here procedures which have been developed for the organisation and management of a multi-site software archive in which items of software may be introduced or updated at any of the participating sites. A simple algorithm is outlined to propagate changes made to all sites, protecting against conflicting changes and ensuring consistency of the archive is maintained. Similar methods are applicable to the management of other kinds of distributed system, especially internet-based information services, including World Wide Web sites which allow regional updates. © 1998 John Wiley & Sons, Ltd.

We introduce and examine some properties of a new complexity measure for Boolean functions. Unlike classical approaches, which are largely concerned with resource requirements, the measure examined here aims at quantifying the potential for lazy evaluation in a function. This measure is motivated by issues arising in the implementation of demand-driven logic simulators. The range of values that can be taken by the measure is precisely identified and a lower bound on the complexity of 'almost all' Boolean functions derived. In addition asymptotically exact values are derived for the class of all Boolean symmetric functions.>

This paper describes an efficient algorithm for generating large combinational circuits (ca. 10 5 -10 6 gates). The method has been applied to construct networks for testing the performance of new VLSI chip fabrication processes and as a means of producing testbeds for assessing the average performance of digital simulation systems

Abstract Vertical migration is a widely acknowledged technique for improving the performance of critical sections of code. Migration may be to the assembly‐language level or, for machines with writable control store, into microcode. The former is easier to implement and allows a degree of portability, albeit limited, of the target routines, although performance gains may not be as great as those resulting from migration into microcode. The latter however, requires considerable programming effort and the size of available control store may well place restrictions upon the amount of code which can be migrated to this level. Given the task of improving the performance of a large software base, full migration is rarely practical, so time must be spent determining the best migration strategy for a ‘target set’ of critical routines. In this paper, we report on work to improve, by vertical migration, the performance of the bask linear algebra subroutines of the FORTRAN NAG library. We identify a number of different migration strategies based upon the availability of two migration levels and report on the performance gains achieved by applying each of these strategies; various conditions under which each strategy may be most appropriate have thus been identified. In particular, this work shows how, by careful selection of just a small number of target routines, resulting performance gains can not only be significant for each individual routine, but also for the whole software system.

Abstract The ability to monitor the progress of a program in execution is useful in program testing and debugging, and for performance analysis and profiling. Systems to support this activity should ideally be high‐level‐language based, but progress in implementing them has been limited by the lack of suitable hardware support. In this paper we derive software structures to support a generalized system of execution monitoring, and define a set of architectural primitives sufficient to support these structures. Simple and efficient means of implementing these primitives within the machine architecture are described.

Abstract Text editors designed for interactive use on visual display units offer significant advantages, particularly in simplicity of use, but non‐visual editors can provide facilities which are difficult to incorporate into a VDU editor without undermining these advantages. This paper describes a text editing system which offers both a visual and non‐visual mode of use, via two user interfaces to a common set of editing primitives, and allows the user to switch freely between modes during the course of an edit. The visual editing interface consists of a set of single‐key control functions which require no unusual VDU characteristics, while non‐visual editing is provided by a set of context editing commands which both duplicate these control functions and offer extra facilities, particularly for repetitive editing.