Software Engineering with Objects

Work Breakdown Stages

Analysis & Design: Part Two

Entity Modeling

Entity (or Data) Modeling provides an understanding of the data used by an organisation, independent of the uses to which it is put to use. It enables an easier construction of a shared data resource by providing an overall blueprint. It facilitates communication between analysts and users, in a form that allows user verification of accuracy. It facilitates construction of robust, enduring physical databases.

Entity Modeling provides an understanding of the entities about which you wish to record data. Entity Modeling moves from the highest-level, least-detailed model to the most detailed. The layers are:

• Corporate data model that describes the overall relationship of all data held or used by the organisation. It is viewed as a collection of inter-related subject databases.
• Subject databases describe, at a high-level, the data of interest to a particular area of the business e.g. Retail, Manufacturing, Personnel, etc. They are normally collections of inter-related entities.
• Logical data models describe at a detailed, but technology and implementation-independent level, the data groups and relationships within a particluar subject database, or system interest area.
• Physical data models describe at a fully detailed level, the exact structure and location of the data as it is physically stored.

The diagram below (still to come) represents the Layers of Data Modeling.

The Entity Relationship Diagram below describes, at a detailed level, but technology and implementation-independent level, the data groups and relationships within the system interest area..

Entity Relationship Diagram

This ERD shows the relationship of an individual with a banking institution and its local branch. The individual has a current and a savings account and can make withdrawals and deposits and transfer funds between accounts. The bank is market driven and appoints client service managers to look after an allocated set of clients. For security and accuracy reasons, all transactions must record the teller through which they were effected. This can be a human or an automated teller machine (ATM).