@techreport{R-94-39, TITLE = {Conceptual Modelling of Physical Systems - a Frame od Reference}, AUTHOR = {Ulf S{\"o}derman}, YEAR = {1994}, NUMBER = {R-94-39}, INSTITUTION = ida, ADDRESS = idaaddr, ABSTRACTURL = {/publications/cgi-bin/tr-fetch.pl?r-94-39+abstr}, ABSTRACT = {The construction of models of physical systems that are adequate for effective model based reasoning is generally recognized as a difficult task. The use of computer aided modelling systems, which provide high-level support and enhance the modelling task, is therefore most attractive. In the Artificiell Intelligence subfield of Qualitative Physics, a number of approaches to representation, automatic selection and composition of models have been proposed over the years. However, these approaches stem from research governed by different goals and motivations and they tend, therefore, to provide their own sets of ontological primitives, their own representation schemes, creation and selection processes, and different illustrating examples. As a consequence it can often be hard to grasp what the proposed approaches have in common and what the differences are.In this paper we present a frame of reference for physical systems modelling. It is intended to facilitate and support future discussions and comparisons of other approaches. In addition, it provides good insight into modelling and may therefore also serve as a useful reference in the development of computer aided modelling systems. The frame takes the form of an approach to modelling in its own right and is referred to as the reference approach.In the reference approach, modelling starts with a real world system, or a design of it, and finishes with a model for prediction of the system's behaviour. In the reference approach we emphasize the conceptual side of modelling and deemphasize the numerical side. The principal contents of the reference approach are: An ontology incorporating a small and well defined set of generic ontological primitives; a network model having a clear syntax and semantics; guidelines for the mathematical characterization; a clear notion of causality; and a causality assignment procedure.}, IDANR = {LiTH-IDA-R-94-39}