ER Model and Business Rules Questions and Answers

Answer: D

It is drawn as a Double Diamond.

In Chen's ER notation a weak entity set is drawn as a double rectangle, and the identifying relationship that links it to its owner (strong) entity set is drawn as a double diamond. This many-to-one identifying relationship is what gives the weak entity its identity.

A plain rectangle is an ordinary entity set and a plain diamond an ordinary relationship. The double rectangle is the weak entity set itself, the usual trap, not the relationship connecting it.

Answer: C

Correct answer: Entity

The rectangle is the entity symbol in an entity-relationship diagram, as the oval is the attribute symbol and the diamond the relationship symbol. Optional participation is shown by cardinality notation on the relationship line rather than by any shape of its own.

Answer: A

Correct answer: Attribute

The oval is the attribute symbol, attached by a line to the entity or relationship it describes. The three basic shapes are quickly learnt: rectangle for entity, oval for attribute, diamond for relationship - and the variants such as the double oval for a multivalued attribute build on them.

Answer: B

Correct answer: False

Clustering groups related entities into a single higher-level object, so the diagram shows fewer symbols. The point is to make a large model readable at a summary level, with the detail visible on decomposing a cluster rather than all at once.

Answer: A

Correct answer: True

Historically the rules were coded into each application that touched the data, which is why the same rule was often implemented several times and inconsistently. Moving them into the database as constraints and triggers, or into a rules engine, is what gives one authoritative statement of each rule.

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.