A little more than a decade ago my colleagues and I faced the necessity for providing a database management system which might commonly serve a number of different types of computer aided design applications at different manufacturing enterprises. We evaluated some wellknown cases of conceptual models and commercially available DBMSs, and found none fuHy meeting the requirements. Yet the analysis of them led us to the development of what we named the Logical Structure Management System (LMS). Syntactically the LMS language is somewhat similar to ALPHA by E. F. Codd. The underly ing conceptual model is entirely different from that of the relational model, however. LMS has been since put into practical use, meanwhile a further ef fort in search of asound theoretical base and a concrete linguistic framework for true product modeling together with comparative studies of various ap proaches has been made. Here, the term product modeling is used to signify the construction of informational models of design objects and design pro cesses in which it must be possible to include not a fixed set of attributes and relations, such as geometry, physical properties, part-of hierarchy, etc., but whatever aspects of design designers may desire to be included. The purpose of this book is to present the major results of the said effort, which are primarily of a theoretical or conceptual nature. Following the intro duction (Chap."