The language that requires a user to specify the data to be retrieved without specifying exactly how to get it is
Answer: B
Correct answer: Non-Procedural DML.
A non-procedural, or declarative, language states what is wanted and leaves the system to work out how to obtain it - SQL is the example. A procedural DML would require the program to navigate to the records itself.
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Precedence graphs help to find a
Answer: A
Correct answer: Serializable schedule.
A precedence, or serialization, graph has a node per transaction and an edge for each conflicting pair. If the graph has no cycle the schedule is serializable; a cycle means it is not. Deadlock is detected with a different graph, the wait-for graph.
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The rule that a value of a foreign key must appear as a value of some specific table is called a
Answer: A
Correct answer: Referential constraint.
A referential integrity constraint requires every value of a foreign key to appear as a key value in the referenced table, so no reference points at a row that does not exist. Integrity constraint is the general category, of which this is one kind.
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The clause in SQL that specifies that the query result should be sorted in ascending or descending order based on the values of one or more columns is
Answer: B
Correct answer: Order by
ORDER BY sorts the result, taking ASC or DESC and one or more columns. GROUP BY collects rows into groups and HAVING filters those groups; neither of them sorts.
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What is a disjoint less constraint?
Answer: A
Correct answer: It requires that an entity belongs to no more than one lower level entity set
A disjointness constraint on a specialisation says the lower-level sets do not overlap, so an entity may be a member of at most one of them. If it may belong to several, the specialisation is overlapping instead.
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According to the levels of abstraction, the schema at the intermediate level is called
Answer: D
Correct answer: Logical schema.
The three levels of abstraction are physical at the bottom, logical in the middle and external, or view, at the top. The logical schema describes the whole database as tables and relationships without saying how it is stored.
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It is an abstraction through which relationships are treated as higher level entities
Answer: C
Correct answer: Aggregation.
Aggregation lets a relationship be treated as an entity, so that another relationship can be defined on it. Generalisation and specialisation relate entity sets to each other rather than promoting a relationship.
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A relation is in ______ if an attribute of a composite key is dependent on an attribute of another composite key.
Answer: B
Correct answer: 3NF
This is the transitive dependency that third normal form forbids: a non-key attribute determining another non-key attribute. Second normal form removes only partial dependencies on part of a composite key, so the relation can satisfy 2NF and still fail here.
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What is data integrity?
Answer: B
Correct answer: It is the data contained in database that is accurate and consistent
Integrity means the data is correct and internally consistent, which is what constraints, transactions and referential rules exist to protect. Security is a separate property, concerning who may see the data rather than whether it is right.
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What are the desirable properties of a decomposition
Answer: B
Correct answer: Dependency preservation.
A decomposition should be lossless - the original relation must be recoverable by joining the pieces - and dependency preserving, so that every functional dependency can still be enforced on a single one of the resulting relations. Redundancy is what decomposition removes, not a property it should have.
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