Formal methods in knowledge engineering

This paper presents a general discussion of the role of formal methods in Knowledge Engineering. We give an historical account of the development of the eld of Knowledge Engineering towards the use of formal methods. Subsequently, we discuss the pro's and cons of formal methods. We do this by summarising the proclaimed advantages, and by arguing against some of the commonly heard objections against formal methods. We brieey summarise the current state of the art and discuss the most important directions that future research in this eld should take. This paper presents a general setting for the other contributions in this issue of the Journal, which each deal with a speciic issue in more detail. Although the history of KBS technology and Knowledge Engineering (KE) is well documented in a number of places in the literature (e.g. 42, ch.2]), in this section we will give an account of the development of KE 1 which will show the natural growth of this eld to the use of formal methods. In the development of KE methods and technology, we distinguish three main periods: the programming period, the modelling period, and the current move towards the introduction of formal methods. The rst era of KE technology stretched from the late '70s to the mid '80s. This period was characterised by the development of new programming techniques. New systems were described in terms of the representation techniques that they employed: rules, frames, Horn clauses, semantic networks, etc. KBS development environments gave support at the level of these representation techniques, and often aimed at integrating these diier-ent representations (e.g ART, KEE, Knowledge Craft, see 43] for a comparison). Such programming techniques were often developed and widely used before a proper formal 1 At least from a European perspective. It is well possible that from an American or Japanese perspective , a diierent picture would emerge.