ISYS114 Lecture Notes - Lecture 3: Subtyping, Widepoint Corporation, Abstract And Concrete

• School: Macquarie University
• Department: Information Systems
• Course: ISYS114
• Professor: Charanya

Document Summary

Enhanced er model: extends original er model with new modelling constructs. Subtype: a subgrouping of the entities in an entity type that has attributes distinct from those in other subgroupings. Supertype: a generic entity type that has a relationship with one or more subtypes. Attribute inheritance: subtype entities inherit values of all attributes of the supertype and an instance of a subtype is also an instance of the supertype. The figure (right) illustrates basic notation for supertype/subtype notation. The figure (left) details basic notation for supertype/subtype notation. Different modelling tools may have different notation for the same modelling constructs. The figure to the right demonstrates an employee supertype with three subtypes. Relationships at the supertype level indicate that all subtypes will participate in the relationship. The instance of a subtype may participate in a relationship unique to that subtype. In this situation, the relationship is shown at the subtype level.