ER Model and Business Rules Questions and Answers

Answer: A

Correct answer: True

An entity cluster is a set of entity types and their relationships treated as one object on a summary diagram. Because a cluster can itself contain clusters, a large model can be presented at several levels of detail, each readable on its own.

Answer: B

Correct answer: Attributes are assigned at the highest logical level.

An attribute shared by every subtype belongs at the supertype, where it is held once and inherited by all. Pushing it down to the subtypes duplicates it and invites inconsistency. The rule is a matter of placing each attribute as high as it is true, and no higher.

Answer: A

Correct answer: True

This is one of the two conditions justifying the construct. If an attribute applies to only some instances, holding it on the single entity type means most rows carry a null, and the null has no meaning - it is not unknown but inapplicable. A subtype gives it a proper home.

Answer: D

Correct answer: Enabler

The three classifications are condition, integrity constraint and authorisation - a rule that must be tested, a rule that must always hold, and a rule about who may do what. Enabler is not among them; it names no distinct kind of constraint on behaviour.

Answer: C

Correct answer: Overlap with partial specialization

The stem states both rules. May be a member of multiple subtypes makes the specialisation overlapping rather than disjoint, and does not have to be a member makes it partial rather than total. This is the exact complement of the disjoint-and-total case, and the two rules remain independent of each other.

Answer: B

Correct answer: False

The disjoint rule states exactly the opposite: an instance may belong to one subtype at most. Membership of more than one is the overlap rule, and the two are alternatives, so the statement has described one rule and named the other.

Answer: A

Correct answer: True

This is the definition. The discriminator is an attribute of the supertype whose value tells which subtype an instance belongs to, so it must be present on every instance and must be examined before the subtype is known.

Answer: A

Correct answer: Defining one or more subtypes of the supertype and forming supertype/subtype relationships.

Specialisation works downward from the general to the particular: an existing entity type is examined, distinct subgroupings are identified, and subtypes are created and linked to it. Generalisation is the reverse process, starting from several specific entity types and abstracting a common supertype from them.

Answer: A

Correct answer: An instance of a subtype participates in a relationship that is unique to that subtype.

A supertype and subtype structure is justified either by attributes that apply only to some instances or by relationships that only some instances participate in. If every instance behaves alike in both respects there is nothing to separate and the subtypes add complexity without meaning.

Answer: B

Correct answer: When a subtype entity inherits values of the supertype attribute

Inheritance runs downward. Attributes common to every subtype are held once at the supertype and are inherited by each subtype instance, so an instance of the subtype carries both the general attributes and its own particular ones. The relationships of the supertype are inherited on the same terms.