Basics of Entity Relationship Modeling



 Entity Relational Diagrams Entity-relationship diagrams aims at modeling given business rule for a certain business scenario. They are mostly used during design stage to identify system elements and their relationships. To draw an entity-relationship diagrams, we must identify business entities, attributes, and relationships. Entities are something about which data is recorded. It is represented in ER diagrams by rectangles and named using singular nouns. Attributes are property trait or characteristic of an entity. Top level ER diagrams do not include attribute for easiness. Relationship describes how business entities interact. From the given business scenario, Department has a one to many relationship with employees and royers. This is because department can employ many employees and each employee is assigned to one department. However, relationship between department and royers is optional since some are not assign any specific department. On the other hand, employee has a one to one relationship with department because one department can be managed my one employee. Division has a one to many relationship with department because one division can operate many departments and one division can operate each department. Since division can be managed by one employee, their association is a one to one relationship. Employees has a one to many relationship with projects. This is because many projects can be assigned to one employee to work on it. Also, one project must be assign to one employee. Client has a one to many relationship with project since one client can sponsor many project. The following is an entity relationship diagram for the given business scenario.