Conceptual Data Modeling Chapter 9. The Entity-Relationship Model/Diagram. Agenda. Conceptual Data Modeling—what and why? Terminology How to Lots of examples. Learning Objectives. After this chapter, you should be able to:
The Entity-Relationship Model/Diagram
1. What do we mean by “conceptual data modeling”?
2. Why is it important?
3. How is it different than other “views” of the business system such as process models (DFDs)?
(a) System user (Treasurer) and output (Expense Report) shown as entities
Entity with a multivalued attribute (Skill) and derived attribute (Years_Employed)
Here: Simple key attribute
(a) Relationship type (Completes)
…as an associative entity
(a) Basic relationship
(a) Mandatory cardinalities
A software training program is divided into training modules, and each module is described by module name and the approximate practice time. Each module sometimes has prerequisite modules. Model this situation of training program with an E-R diagram.
Each semester, each student must be assigned an advisor who counsels students about degree requirements and helps students register for classes. Students must register for classes with the help of an advisor, but if their assigned advisor is not available, they may register with any advisor. We must keep track of students, their assigned advisor, and with whom the student registered for the current term. Represent this situation of students and advisors with an E-R diagram.
What if some students are also advisors? Hint: use supertypes/subtypes.