Object-Oriented Database Questions and Answers

Answer: A

Correct answer: False

The general term for a collection of literals or object types is a collection, and a bag is only one of its kinds - the unordered one that permits duplicates. Sets, lists and dictionaries are equally collections of literals or object types, so naming the general category after one of its members is wrong.

Answer: A

Correct answer: False

An attribute’s value may be a literal or an object identifier, so always literal is too strong. Where the value is an object reference, however, a relationship is generally the better construct, since it is declared in both directions and its integrity is maintained by the system.

Answer: D

Correct answer: All of the above.

Atomic literals are the indivisible values: the numeric types including long, the character and string types, boolean, and the enumerated types. They are contrasted with collection literals such as set and bag, and with structured literals built from other literals.

Answer: A

Correct answer: True

Only unary and binary relationships are provided for. Anything of higher degree must be represented by promoting the relationship itself to a class, which is then joined by binary relationships to each participant - the same device the relational model uses for a ternary association.

Answer: B

Correct answer: False

Database objects are almost always persistent - they outlive the program that created them, which is the whole purpose of a database. Transient objects exist only for the duration of a program run, and an object database distinguishes the two explicitly.

Answer: A

Correct answer: True

That is what a key does, in this model as in the relational one. Declaring a key constrains the extent so that no two of its objects share the same value for the key attribute or combination of attributes - which is why the extent must be declared first.

Answer: A

Correct answer: ABC123

The declaration follows the usual type-then-name order, so ABC123 is the class and course is the name being declared. The parentheses mark it as an operation rather than an attribute, and ABC123 is then the type it returns.

Answer: A

Correct answer: True

This is the essential distinction between a literal and an object. An object has an identifier which persists independently of its values, so two objects with identical attribute values remain distinct and either can be referenced. A literal is simply a value: it has no identity, so it can only be embedded within an object rather than pointed at.

Answer: C

Correct answer: Relationship

Because the model requires a relationship to be declared from both ends, each declaration names the corresponding declaration in the other class with the inverse keyword. The database can then keep the two consistent automatically, so adding a link at one end creates it at the other.

Answer: B

Correct answer: False

ODL permits several tag names for one object identifier, which is useful when the same object is known by different names in different contexts. The identifier itself remains single and unique; it is only the names by which it may be reached that can be multiple.