ER Model Limitations
Prior to beginning this discussion, read Chapter 3: The Relational Database Model and Chapter 4: Entity Relationship (ER) Modeling from the course text. In addition, you may also want to complete problems 24, 25, 26, 27, 28 in Chapter 3. These problems will teach you how to use the entity relationship diagram to graphically create a logical view of the database, and it will assist you in completing this discussion.
Entity relationship models are limited in what they can express. It helps to be aware of the limitations up front, since they can affect the choices you make as to how you represent the enterprise you are modeling. Describe some of the ER design limitations, and discuss how understanding these limitations will influence how you choose to model a particular situation, so that you are able to represent the things that are most important.
Enhanced ER Model
Prior to beginning this assignment, review Chapter 3: The Relational Database Model and Chapter 4: Entity Relationship (ER) Modeling from the course text and read Enhanced Entity-Relationship Model. A superclass is an entity type that has one or more distinct subgroups with unique attributes. The subgroups with unique attributes are defined as subclasses. There are several reasons for introducing superclass and subclasses into an ER model. First, incorporating a superclass and subclasses maintains the cleanliness of the structure and improves the conceptual flow. Second, it adds familiar semantic information to an ER diagram. For this interactive assignment,
- Explain when we consider using subtypes.
- Create an ER diagram that depicts a superclass (entity: Person) and subclass (entities: Faculty, Staff, Student). Make sure to include at least three attributes for each entity. For instance, the STUDENT subclass has attributes such as MajorDept, Class, and GPA.
Attach your ER diagram with your response in your initial post.