Pergamon Expert Systems With Applications, Vol. 10, No. 2, pp. 223-231, 1996 Copyright © 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0957-4174/96 $15.00+0.00 0957-4174(95)00048-8 Object-Oriented Approach to a Knowledge-Based Structural Design System KYUNG-Ho LEE *l, DONGKON LEE l AND SOON-HUNG HAN 2 zKoreaResearchInstituteof Ships and Ocean Engineering, YusungP.O.Box 101,DaedukScience Town,Taejon,Koreaand 2Korea Advanced Institute of Science and Technology, Taejon,Korea Abstract--In this article, an Expert System for MIDship section design (ESMID) is developed based on a general-purpose expert system shell. The system focuses on the integration of knowledge-based system and design resources such as an engineering database, graphical user interface, and engineering application programs for the calculation of section modulus and longitudinal strength of ship structure. The validation of the ESMID system was examined and verified by applying the system to the 64K bulk carrier ship. The developed expert system can help a novice engineer in designing the midship section o f ship. 1. ~TRODUCTION EXPERT SYSTEMS have been developed as stand-alone systems, but the current trend of expert system develop- ments puts emphasis on integration with existing system environments (Liebowitz, 1995). That is, expert systems are integrated with database, graphical user interface (GUI), and engineering application programs which are implemented in C, Fortran, or some other language. Especially, there have been efforts to apply artificial intelligent methodologies to engineering design prob- lems (Doe et al., 1991; Gefo, 1991; Maccallum, 1991; Yano, Ohsuga, & Hori, 1992; Kim, 1993; Balachandran, 1993; Lee et al., 1992). Intelligent CAD systems can be developed to guide and support ship designers. In this paper an expert system based on a general purpose expert system shell, Nexpert Object, is presented. The system will be useful for novices in ship design when designing the midship section. Also studied are knowledge representation based on object-oriented concepts, integration of knowledge-bases and databases, and system integration through applica- tion programming interface (API) technique. In order to represent complex and experimental knowledge of design experts, object-oriented knowledge representation is adopted. Extracted knowledge is repre- sented by objects, classes, methods and rules through grouping and making a hierarchy of them. In particular, dynamic objects and methods were used to reduce complexity of rules. * To whom all correspondenceand requests for reprints should be addressed. The interface of knowledge-bases and databases is very important for the construction of engineering expert systems. This paper describes techniques for the inter- face of knowledge-base and the ORACLE relational database. An API program for the structural design of ships is developed using a callable interface available in expert system shell. A GUI based on Motif and X-window system are adopted to construct a user friendly expert system for the structural design system of ships. Visualization of the reasoning process by GUI can greatly help designers design ships. 2. PROCESS OF THE SHIP STRUCTURAL DESIGN The ship structure must have strength strong enough to protect human lives, cargos and ship from sea state. On the other hand, the structural weight is constrained by other factors such as the profitability of the builder. Therefore the designer must perform ship structural design to solve the above conflicting notions. The process of the ship structural design using rules for classification is shown at Figure 1 (Lee et al., 1987). The indication part (square box in the middle) which is the focal point of this paper is composed of three jobs (Bannerman & Jan, 1980; Hughes, 1983). The first job is to determine the minimum requirement values of the structural members according to rules for classification. The second is to perform the iterative design in order to satisfy the required structural strength. 223