Specialization denoted in ER Diagram - Database

Q.  How is specialization denoted in an ER Diagram?
- Published on 19 Oct 15

a. Triangle labeled IS A
b. Rectangle labeled IS A
c. Rectangle Labeled HAS A
d. Triangle labeled HAS A

ANSWER: Triangle labeled IS A

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    Discussion

  • Nirja Shah   -Posted on 30 Oct 15
    Generalization/Specialization
    - It is depicted by a triangle component labelled ISA (E.g. customer “is a” person).

    Constraints of Generalization or Specialization
    - It is whether or not entities may belong to more than one lower-level entity set within a single generalization.

    - Disjoint - It is an entity that can belong to only one lower-level entity set

    - Noted in E-R diagram by writing disjoint next to the ISA triangle

    - Overlapping - It is an entity that can belong to more than one lower-level entity set

    - Completeness constraint specifies whether or not an entity in the higher-level entity set must belong to at least one of the lower-level entity sets within a generalization.

    - Total - It is an entity that must belong to one of the lower-level entity sets

    - Noted in E-R diagram by a double line over the ISA triangle

    - Partial - It is an entity that need not belong to one of the lower-level entity sets

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