Representation of knowledge in a program for solving physics problems

Rather than using a single uniform representation, the program uses a number of different representations, each of which is specialized for a particular task, e.g., language syntax, language semantics, representing objects and their attributes and relationships, representing objects as canonical objects used in physics, modelling geometry, and solving equations. Many of these representations are based on the notion of frames [Minsky 75]. The use of specialized representations simplifies many of the processes which must be performed by the program; however, it requires that the program be able to translate between the various representations when necessary. Procedural knowledge is required to convert one representation into another, since it frequently happens that information which is essential in the target representation is unspecified or is specified only implicitly in the source representation; inferences are required to fill in such information. Specialized representations allow procedures to be attached to particular types of representations, both to convert them to other types and to solve problems which are associated with the specialized area. In this paper, we discuss the ways in which these techniques are used to coordinate the many kinds of knowledge which are necessary for solving physics problems.