You may specify an object identifier with only one unique tag name.
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.
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The Object Model supports different literal types, but does not support atomic literals, collection literals, and structured literals.
Answer: B
Correct answer: False
The model supports all three kinds. Atomic literals are the indivisible values such as long and boolean; collection literals are sets, bags, lists and dictionaries; and structured literals are records built from other literals. The statement denies exactly the three categories the model defines.
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Using OQL, you may do which of the following?
Answer: D
Correct answer: All of the above.
OQL provides select for a filtered subset, select distinct for a collection without duplicates, and a plain selection that returns everything including duplicates. The parallel with SQL is deliberate, so that a query language familiar from the relational world carries over to objects.
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An attribute's value is either a literal or an object identifier.
Answer: A
Correct answer: True
An attribute may hold a literal value or an object identifier referring to another object. The model does not forbid the second, though where a genuine association between two classes is meant, a relationship is the better construct because the system then maintains it in both directions.
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In ODL, you specify an operation using parentheses after its name.
Answer: A
Correct answer: True
The parentheses are what distinguish an operation from an attribute in a class declaration, and they hold the parameter list when there is one. ODL declares only the signature; the implementation is written in the host programming language.
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The object definition language (ODL) is which of the following?
Answer: D
Correct answer: All of the above.
ODL does all three. It is the data definition language of the ODMG model, it is used to write the logical schema, and since it is directly executable by an object database it is also the means by which that schema is implemented - which is what removes the translation step the relational world needs.
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An ordered collection of elements of the same type are called sets.
Answer: B
Correct answer: False
An ordered collection of elements of the same type is a list. A set is unordered and holds no duplicates. The four collection types are separated by exactly these two properties, order and the admission of duplicates, and confusing two of them is the standard trap in this material.
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ODL supports which of the following types of association relationships?
Answer: B
Correct answer: Unary and Binary
The ODMG object model provides for relationships between two classes and for a class related to itself, and no further. A ternary relationship must be modelled by introducing a class of its own to stand for the association, exactly as an associative entity is used in the relational model.
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If you know all the possible values that an attribute can have, you can enumerate those values in ODL.
Answer: A
Correct answer: True
An enumerated type does exactly this: the permitted values are listed in the schema, and the attribute can hold none but those. It documents the intent and enforces the constraint at the same time, without any code in the application.
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ODL supports the abstract keyword for classes and operations.
Answer: B
Correct answer: False
ODL has no abstract keyword. Abstract classes are represented in the model by other means, but the language does not provide a modifier for them - nor for operations, which are declared with their signature and implemented elsewhere in any case.
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