Week 11: Extended Entity Relationship Model

These flashcards cover the key concepts from the Extended Entity Relationship Model lecture notes.

What are the three levels of data abstraction?

External model, Conceptual model, Internal model.

What is an entity supertype?

A generic entity type that is related to one or more entity subtypes and contains common characteristics.

What is an entity subtype?

An entity subtype contains unique characteristics specific to that subtype.

What defines disjoint subtypes?

Disjoint subtypes are also known as non-overlapping subtypes, which contain a unique subset of the supertype entity set.

What are overlapping subtypes?

Subtypes that contain nonunique subsets of the supertype entity set.

What is the purpose of the external model?

It represents the end-user's view of the data environment and helps identify specific data required for business operations.

What characterizes the conceptual model?

It represents a global view of the entire database and is independent of both software and hardware.

What is the physical model concerned with?

It describes how data are saved on storage media like disks or tapes, and it is software and hardware dependent.

What is specialization in data modeling?

A top-down process identifying lower-level, specific entity subtypes from higher-level entities based on unique characteristics.

What is generalization in data modeling?

A bottom-up process identifying higher-level, generic entity supertypes from lower-level entity subtypes by grouping common characteristics.

What does the subtype discriminator do?

It determines to which entity subtype each supertype occurrence is related and uses equality comparison for its default condition.

What is the completeness constraint?

Specifies whether each entity supertype occurrence must also be a member of at least one subtype, which can be partial or total.

What are the advantages of the external model?

It simplifies application program development, ensures security constraints, and aids designers by providing feedback.

What defines a specialization hierarchy?

It depicts the arrangement of higher-level entity supertypes and lower-level subtypes based on unique relationships.

What is inheritance in the context of data modeling?

It allows entity subtypes to inherit attributes and relationships of their supertype.