Lecture Database management systems - Chapter 2: Entity relationship model. This chapter includes contents: Introduction, overview of database design, ER model basics, symbols used in ER diagram, attribute classification, ER diagram, relationship degree, relationship classification,. | Chapter 2 Entity Relationship Model Introduction Modeling databases using a graphical technique is proposed so that humans can relate to easily. ER Model is based on a perception of a real world that consists of collection of basic objects called entities and relationships among these objects. Overview of Database Design Conceptual design: (ER Model is used at this stage.) A database “schema” in the ER Model can be represented pictorially (ER diagrams). The next step in DB design is the actual implementation of the database, using a commercial DBMS By using the DBMS, conceptual design from high-level data model will be transformed into the implementation data model. COMPANY example The COMPANY database keeps track of company’s employee, departments, and projects Suppose that after the requirement collection and analysis phase, the database designers provide the following description: COMPANY example The company is organized into DEPARTMENTs. Each department has a name, number and an employee who manages the department. The start date of the department manager will be kept track. A department may have several locations. Each department controls a number of PROJECTs. Each project has a unique name, unique number and is located at a single .
