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What is a disjoint less constraint?

  • A.It requires that an entity belongs to no more than one level entity set.
  • B.The same entity may belong to more than one level.
  • C.The database must contain an unmatched foreign key value.
  • D.An entity can be joined with another entity in the same level entity set.

Answer: A

Correct answer: It requires that an entity belongs to no more than one lower level entity set

A disjointness constraint on a specialisation says the lower-level sets do not overlap, so an entity may be a member of at most one of them. If it may belong to several, the specialisation is overlapping instead.

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