Modeling Data in the Organization Questions and Answers

Answer: A

Correct answer: Declarative

A good business rule states what must be true rather than how to achieve it, so it can be implemented in whatever way suits the technology and can be validated by the people who own it. The other three are faults: imprecision leaves it unenforceable, redundancy invites contradiction, and a compound rule should be split into its parts.

Answer: B

Correct answer: False

A derived attribute is calculated from other attribute values - an age from a date of birth, a total from unit price and quantity. Deriving it from a relationship is not the definition. The reason for marking it as derived is that its value must never be stored and updated independently of the values it comes from.

Answer: B

Correct answer: A relationship between two entities

The degree of a relationship counts the entity types taking part: unary for one, binary for two, ternary for three. Binary relationships are by far the commonest, and a relationship of higher degree can often be replaced by an associative entity joined to each participant by a binary relationship.

Answer: D

Correct answer: Weak entity

An entity that cannot exist without another - a dependant without an employee, a line item without an order - is a weak entity, and the relationship joining it to the entity it depends on is an identifying relationship. Its identifier includes the identifier of the owner, since it has no independent existence to be identified by.

Answer: A

Correct answer: Mandatory one

The two figures answer two different questions. The minimum says whether participation is required: one means it is, so the relationship is mandatory. The maximum says how many are permitted: one means at most a single instance. Together they give mandatory one.

Answer: B

Correct answer: Follow a standard format

Attribute names should follow a consistent convention across the model, typically including the entity name or an abbreviation of it, so that the same concept is named the same way everywhere. They are nouns rather than verbs, and aliases are recorded in the repository rather than used as names.

Answer: B

Correct answer: False

A person, place, object or event in the user environment is an entity. An attribute is a property or characteristic of an entity - the employee’s name, the order’s date. The statement has given the definition of one under the name of the other.

Answer: A

Correct answer: True

Two attributes of the same entity type with the same name could not be told apart, so uniqueness within the entity is a requirement rather than a convention. Across entity types the same name may recur - both a customer and a supplier have a name - which is why the naming standard usually qualifies attributes with their entity.

Answer: B

Correct answer: False

A relationship associates entities, not attributes. Attributes describe the entities and relationships they belong to; they do not associate with one another. Substituting one term for the other reverses the structure of the model entirely.

Answer: B

Correct answer: Entity

The rectangle is the entity symbol. The three shapes to know are rectangle for entity, oval for attribute and diamond for relationship; cardinality and optionality are shown by marks on the relationship lines rather than by shapes of their own.