A METHODOLOGY FOR DERIVING AN ENTITY-RELATIONSHIP MODEL-BASED ON A DATA-FLOW DIAGRAM

Abstract

This article descirbes an object-oriented methodology for deriving an entity-relationship (ER) model from requirements specified in a data flow diagram (DFD). The methodolgy is top down. It begins with an analysis of the objects described in the DFD to produce an object model. Modeling objects instead of individual data items reduces the number of data elements with which the analyst must be concerned initially. Next, information about data synonyms and interdependency is considered to refine the object model. Guidelines for removing redundant, overlapping descriptions of objects are also proposed and the object model is transformed into an ER model by applying a set of abstraction heuristics. The methodology integrates the DFD-based structured analysis methodology and the ER model so that process and data requirements can be analyzed simultaneously. It enables the system developer to understand the relationships between the processes (embedded in the DFD diagram) and data (described in the ER model) at the early stage of system analysis. Moreover, changes of requirements, either in process or in data, can be correlated easily to foster a quality design of the final system. This methodology can facilitate application development based on an existing data base or on an entirely new data base.