Which of the following is an unordered collection of elements that may contain duplicates?
Answer: B
Correct answer: Bag
A bag is unordered and permits duplicates, which is what distinguishes it from a set. The four collection types divide on exactly these two properties: a set is unordered without duplicates, a bag unordered with them, a list ordered, and a dictionary a collection of key-value pairs.
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A collection of literals or object types is called a bag.
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.
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An attribute's value is always literal.
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.
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An atomic literal is which of the following?
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.
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The ODMG Object Model supports only unary and binary relationships.
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.
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Database objects are almost always transient.
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.
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Specifying a key ensures that no two objects belonging to a class have the same value for the key attribute(s)
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.
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Identify the class name for the following code: ABC123 course();
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.
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Literals do not have identifiers, and, therefore, cannot be individually referenced like objects.
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.
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The keyword "inverse" is used in which of the following?
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.
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