Author : Emmanuel G. Theodossakis
Publisher :
ISBN 13 :
Total Pages : 164 pages
Book Rating : 4.:/5 (117 download)
Book Synopsis Specification of Conceptual Database Schema Languages by : Emmanuel G. Theodossakis
Download or read book Specification of Conceptual Database Schema Languages written by Emmanuel G. Theodossakis and published by . This book was released on 1988 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: In a database design process the database model used is essential for producing a good conceptual schema. In most database models, like IMS and CODASYL, a conceptual schema contains too many implementation details which complicate the designer's task. The conceptual schema of a relational database hides too much information from the user, because it lacks the necessary structure. The standard E-R model has more structure and is easy to use. But, it still lacks the ability to express certain types of abstract concepts needed in most design processes. In this work an extended E-R model is used, which includes abstraction hierarchies. A conceptual schema language (EXERM-CSL), extended in order to include abstraction hierarchies, is proposed to define the structural part of the model. The integrity part of the model has also been included. No model would be complete without the manipulative part. Many languages have been proposed for the E-R model. Some of them take advantage of a schema graph, as for instance GORDAS. Others are based on the concept of simplified completeness, like Executable Language for instance. In this work we propose a high-level query language (EXERM-DML), which not only makes use of the E-R diagram, but it is also based on the Reshaped Relational Algebra (RRA), which gives more expressive power to the language itself. EXERM-DML also makes provisions for abstraction hierarchies. Finally EXERM-DML is a complete database language as far as retrieval, insertion, and updating of data is concerned.