This book gives a theoretical base and a perspective for the analysis, design, and operation of information systems, particularly their information storage and retrieval (ISAR) component, whether mechanized or manual. Information systems deal with many types of entities: events, persons, documents, business transactions, museum objects, research projects, and technical parts, to name a few. Among the purposes the serve are to inform the public, to support managers, researchers, and engineers, and to provide a knowledge base for an artificial intelligence program. The principles discussed in this book apply to all these contexts. The book achieves this generality by drawing on ideas from two conceptually overlapping areas - data base management and the organization and use of knowledge in libraries - and by integrating these ideas into a coherent framework. The principles discussed apply to the design of new systems and, more importantly, to the analysis of existing systems in order to exploit their capabilities better, to circumvent their shortcomings, and to introduce modifications where feasible.