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How Does Your Case-Base Grow ?

1 Introduction Case-based reasoning (CBR) systems solve problems by reusing the solutions to similar problems stored as cases in a case base [1]. Recent research has looked at the competence of case-bases and, in particular, ways of measuring and predicting this competence. To date, a number of effective competence models have been proposed [3,6,8]. This paper investigates the evolution of competence in a case-base and its main contribution is the documentation of a characteristic competence behaviour for CBR systems. Section 2 briefly outlines our current competence model. The main thrust of our work is contained in Section 3 where we demonstrate that a case-base evolves in a predictable and characteristic way with respect to competence. In fact, we show that there is a characteristic competence curve for CBR systems, just as many machine learning systems have a characteristic efficiency curve associated with the utility problem [2,4,5]. We demonstrate how a case-base moves predictably through four distinct developmental phases as it evolves and we argue that this is an important step forward when it comes to understanding the true nature of competence in CBR systems. Competence is all about the number and type of target problems that a given system can solve. The competence model described in this section is based upon on a similar model first introduced by Smyth & McKenna [8]. When we talk about the competence of a case we are referring to its ability to solve certain target problems. Consider a set of cases, C (such that each case is composed of a description and a solution part), and a space of target problems, T (each target consisting of a problem description only). A case, c∈C, can be used to solve a target, t∈T, if and only if the case is retrieved for the target, and it is possible to adapt its solution so that it solves the target problem [6, 7] (see Defs 1-3). Def. 1: RetrievalSpace(t∈T)={c∈C: c is retrieved given t} Def. 2: AdaptationSpace(t∈T)={c∈C: c can be adapted to solve t}