A data model, called the entity-relationship model, is proposed. This model incorporates some of the important semantic information about the real world. A special diagrammatic technique is introduced as a tool for database design. An example of database design and description using the model and the diagrammatic technique is given. Some implications for data integrity, infor-mation retrieval, and data manipulation are discussed. The entity-relationship model can be used as a basis for unification of different views of data: t,he network model, the relational model, and the entity set model. Semantic ambiguities in these models are analyzed. Possible ways to derive their views of data from the entity-relationship model are presented. Key Words and Phrases: database design, logical view of data, semantics of data, data models, entity-relationship model, relational model, Data Base Task Group, network model, entity set

Record structures are generally efficient, familiar, and easy to use for most current data processing applications. But they are not complete in their ability to represent information, nor are they fully self-describing.

Conceptual modelling refers to the part of system development that involves investigating the problems and requirements of the users community and from that, developing a specification of the desired system. Conceptual modelling addresses two major aspects: the conceptual product (the so-called conceptual schema) and the conceptual process (the modelling process to deliver the conceptual product). Contributions to the field of conceptual modelling have emphasized the product aspect. A large variety of conceptual models have proposed high level concepts and abstraction mechanisms by which systems may be described at a conceptual level. Conceptual models have proved to be extremely useful throughout the information system life cycle and, hence, to be one of the most fundamental tools in the area of information systems engineering. However the growing demand for large and complex information systems calls for the introduction of new and more precise, formal techniques to model reality....

Concep..Represented by_System Moles The design of Level 4 includes four modules, each of which repre- sents an abstract concept visible to the system end-user. The RELATION module, for example, defines the operations by which users are able to create, modify, and view the primary data objects (relations) of this level. Likewise, the TUPLE module enables users to create and manipulate n-tuples as seperate entities. The AUTHORIZATION module relates to the concept of security in the data base system. Through the operations of this module it is possible to create authorizations which are assertions defining the allowable user accesses to the abstract data objects of Level 4. Certain operations also make it possible to scan all defined authorizations to determine if a user has access to a specified data object. The INTEGRITY module provides operations for defining and maintaining the semantic integrity of relations. For example, it is possible to create assertions which define allowable of these.