ENTITY-RELATIONSHIP BASED DATABASE MANAGEMENT SYSTEM

Abstract

A three level schema architecture Entity-Relationship based Database Management System was proposed in [21]. The conceptual schema is represented by a Normal Form Equity-Relationship diagram [19]. The internal schema is represented by a set of Normal Form not necessarily normalized relations. The external schema is represented by ER diagrams (not necessarily in normal form). The power of the ER based DBMS can be enhanced by allowing the external schemas to be modeled by the Network, Hierarchical or Relational model. This dissertation will present rules for constructing the Network, Hierarchical or Relational model external schema from the conceptual schema in Normal Form ER diagram. The updatability of each of the external views will also be examined. At the time that the Entity-Relationship Model (ERM) was defined, no query languages was specifically introduced for the Entity-Relationship Model. Since then various query languages have been suggested the for ERM [3,14,23,25,27,28]. In the second part of this dissertation some query languages will be surveyed. The languages will be divided into two groups – graphical query languages. The criteria which will be used for comparison include case of use, language features and expressive power. For graphical query languages, user friendliness is of prime importance white expressive power is an import design criteria for non-graphical query languages.