3. Enhanced ERD Flashcards
What is an enhanced ER model?
An enhanced ER model extends the original ER model with additional modeling constructs, such as supertypes and subtypes, to capture more detailed data relationships.
What is a subtype in database modeling?
A subtype is a subgrouping of entities within an entity type that possesses distinct attributes not shared by other subgroupings, while inheriting all attributes from its supertype.
What is a supertype in database modeling?
A supertype is a generic entity type that contains common attributes shared by its subtypes.
What is attribute inheritance in the context of supertypes and subtypes?
Subtype entities inherit all the attributes of their supertype, meaning any instance of a subtype is also an instance of the supertype.
How are relationships handled between supertypes and subtypes?
Relationships defined at the supertype level apply to all subtypes, while relationships unique to specific subtypes are modeled at the subtype level.
What is generalization in ER modeling?
Generalization is a bottom-up process of defining a more general entity type from several specialized entity types.
What is specialization in ER modeling?
Specialization is a top-down process of creating one or more subtypes from a supertype to capture attributes unique to each subgroup.
What are completeness constraints in supertypes/subtypes relationships?
Completeness constraints determine whether every instance of a supertype must also be a member of at least one subtype (total specialization) or if membership is optional (partial specialization).
What are disjointness constraints in supertypes/subtypes relationships?
Disjointness constraints specify whether an instance of a supertype can belong to only one subtype (disjoint rule) or to multiple subtypes (overlap rule).
What is a subtype discriminator?
A subtype discriminator is an attribute of the supertype whose value determines the specific subtype an instance belongs to, and it can be defined as simple or composite.
Why are subtypes used in relational database modeling?
Subtypes are used to represent common data with additional specific attributes, enforce referential integrity, improve query performance, and reduce the occurrence of null values.
How do supertypes and subtypes improve data modeling?
They allow for a clear separation of common and unique attributes, leading to a more organized, efficient, and maintainable database schema.
