Declarative and procedural object-based knowledge modelling

Knowledge-based systems can not only rely on declarative knowledge to solve realistic problems, whatever the domain involved. They have to incorporate some form of procedural knowledge, such as procedures written in an imperative language. Early rule-based systems thus allowed calling of external procedures in the "action" part of the rules. Frame-based systems proposed the procedural attachment mechanism which allows computation of unknown slot values. These facilities were introduced in order to open the knowledge-based systems toward their environment and procedural knowledge was not really considered as a component of the knowledge base. When it clearly appeared that a large part of knowledge was indeed efficiently available as executable procedures, the problem became one of allowing real integration of declarative and procedural knowledge into operational knowledge-based systems. Object-based knowledge models offer excellent potential for such an integration. Extensions of the basic procedural attachment mechanism, together with the notion of task and task classification and decomposition, thus support the development of knowledge-based systems which are able to assist a user in selecting and chaining up methods to solve a global problem, for example of data analysis or equation system solving.<>