Data Abstraction and the Extended ER Model (EER)
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1
What is the external model in data abstraction?
It represents the end users’ view of the data environment and supports security and application development.
2
What does the conceptual model represent?
The global view of the entire database, identifying main data objects and remaining independent of hardware and software.
3
What is the internal model in data abstraction?
It represents the database as seen by the DBMS and maps the conceptual model to the internal schema.
4
What does the physical model describe?
How data are stored on physical media, depending on specific hardware and software.
5
What is the Extended Entity Relationship (EER) model?
A model that adds more semantic constructs to the ER model, represented in EER diagrams.
6
What is an entity supertype?
A generic entity type that contains common characteristics shared by one or more subtypes.
7
What is an entity subtype?
An entity type with unique characteristics not found in the supertype.
8
What is a specialization hierarchy?
A structure showing relationships between higher-level supertypes and lower-level subtypes in “IS-A” form.
9
What is inheritance in EER?
The ability of subtypes to inherit attributes and relationships from their supertype, including the primary key.
10
What is a subtype discriminator?
An attribute in the supertype that identifies the correct subtype of each occurrence.
11
What is specialization?
A top-down process of identifying more specific subtypes from a supertype based on unique characteristics.
12
What is generalization?
A bottom-up process of forming a supertype from subtypes based on common characteristics.
13
What are disjoint subtypes?
Subtypes where each occurrence belongs to only one subtype.
14
What are overlapping subtypes?
Subtypes where occurrences may belong to multiple subtypes simultaneously.
15
What is the completeness constraint?
A rule specifying whether each supertype occurrence must belong to at least one subtype (partial or total).
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