Concepts for Knowledge-based System Design Environments I. System Design and Iiodelling Enterprise 1 Synergies

The paper sets up a conceptua I framework for constructing knowledge-based, computer-aided environments for system design. The framework is based on the formal structures underlying the expert system design methodology being developed by Zeigler [18], name 1 y that of the system entity structure and experimental frame. The system entity formalism is emp I oyed to structure the family of design configurations. The rules for design model synthesis are generated by pruning the design entity structure with respect to generic experimental frames [I33 that represent the design objectives. This leads to a methodology for design of system design envirohments which recognizes three primary relationships of the application domain that must be modelled: the decomposition hierarchy (of the system being des i gned) , the taxonomi c structure (determining the design alternatives), and the coup l i ng constraints (restricting the combinations in which components can be synthesized into the target system). I. SYSTEM DESIGN AND IIODELLING ENTERPRISE 1 SYNERGIES --The process of design is a transformation of a designer’s ideas and expertise into a concrete implementation. This process is driven by the design requirements provided by the client and the available technology. The growing complexity of sys terns being designed has strongly influenced research efforts in constructing computerized support environments for assistance in the design process [4,5,11,12,15]. Our primary goal in this paper is to embed system design within the multifacetted modelling framework [1,8,16,171 and thus provide a systematic design methodology supper ted by adequate forma I structures. We shall argue that such an approach is amenable to computerization and direct application of expert systems and Al techniques. As i I lustrated in Figure 1, system design is brought into the multifacetted framework, with the design process being supported by the modelling and simulation techniques, in the following contexts: a.) Model 1 ing is a creative act of individuals using basic problem-solving techniques, building conceptual mode I s based on knowledge and perception of reality, requirements and objectives of the modelling project. Thus, considering models as design “blueprints” we establish a direct relationship with the modelling enterprise. b.) By providing mechanisms for model decomposition, hierarchical specification and aggregation of partial models. the multifacetted modelling fully responds to the needs of the design of large scale Systems. c.) By providing a spectrum of performance evaluation d.) Bernard P. Zeigler Dept. of Electrical and Computer Engineering University of Arizona Tucson, Arizona 85721 methods including the trade-off measurements and evaluation of multi-level, multi-component, hierarchically specified models, our framework al lows the designer to describe the attributes of designs in comparative measures. This I eads eventually to the choice of the best design with respect to performance measures under consideration. The representation schemes offered by the multifacetted methodology are well structured and have formalized operations that can exploit such structures. This significantly reduces the effort of designing expert environments for a given problem domain. With the above i SSUeS in mind, we shal I present concepts for constructing knowledge-based design environments. The two key forma I objects in our approach are the system entity structure and the aeneric experimental frame. The entity structure is based on a tree-like graph encompassing the system boundaries and decompositions that have been conceived for the system. As we shall describe it in detail in Section 3 the entity structure formal ism is a knowledge representation scheme that facilitates expressing the decomposition hierarchy, the taxonomy of the objects it represents, and the coup1 i ng constraints on the ways in which system components identified in the decompos i t i on hierarchy can be coupled together. The generic experimental frame is a structure that represents a set of design objectives in the form of standard variable types. Such standard variable types express measures of input/output performance, utilization of resources, reliability assessments etc. In outline, these two structures play the following role in our design framework: ,t the system entity structure is a basic means of organizing a family of possible configurations of the system being designed. -5 the objectives and requirements of the design project i nduce appropriate generic experimental frames. zr the design entity structure is pruned with respect to the generic frames. This results in a family of design configurations that conform to the design objectives. a* the pruned substructures sewe as skeletons for generating rules for synthesis of design models. * resulting models are evaluated in respective experimental frames and the best design models are chosen on the basis of such evaluations. We shall provide a detailed exposition of this approach in the ensuing sections. However, let us