The graphical representation of a query is .
Answer: C
Correct answer: Query Tree
A query tree represents a relational algebra expression: the leaves are the relations and each internal node an operation applied to the results below it. The optimiser transforms the tree to find a cheaper equivalent.
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Union operator is a :
Answer: C
Correct answer: Binary Operator
Union takes two relations and produces one, so it is binary. Selection and projection are unary; there are no ternary operators in relational algebra.
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Relations produced from an E-R model will always be
Answer: A
Correct answer: First normal form.
Mapping an E-R model produces tables whose entries are single atomic values, which is precisely first normal form. The higher normal forms depend on the functional dependencies among the attributes and are not guaranteed by the mapping.
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Manager salary details are hidden from the employee .This is
Answer: A
Correct answer: External level data hiding.
Hiding a column from one group of users is done by giving them a view that omits it - that is, by defining a restricted external schema. The conceptual schema still contains the salary; what differs is what each user is shown.
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Which of the following is true for network structure?
Answer: A
Correct answer: It is a physical representation of the data.
The network model links records with physical pointers, so the structure the programmer sees is the structure on disk. That is its chief weakness against the relational model, and it is also why it is not conceptually simple.
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Which two files are used during operation of the DBMS?
Answer: C
Correct answer: Data dictionary and transaction log
The data dictionary is consulted for the description of every object referred to, and the transaction log is written for every change so that recovery is possible. Both are in use continuously while the system runs.
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A list consists of last names, first names, addresses and pin codes. If all people in the list have the same last name and same pin code a useful key would be
Answer: C
Correct answer: the compound key first name and last name
If everyone shares the same last name and pin code, neither of those distinguishes anybody, so neither can be a key. Combining the first name with the last gives the only combination among the options that can vary from person to person.
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In a B-tree the number of keys in each node is ______ than the number of its children.
Answer: A
Correct answer: one less
In a B-tree the keys in a node separate the ranges covered by its children, so n keys divide the range into \( n+1 \) intervals and the node has \( n+1 \) children. The number of keys is therefore one less than the number of children.
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The drawback of shadow paging technique are
Answer: D
Correct answer: All of these
Shadow paging avoids undo and redo but pays for it in three ways: committing means switching page tables and flushing, related pages become scattered because updates are written elsewhere, and the superseded pages have to be reclaimed afterwards.
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Which normal form is considered adequate for normal relational database design?
Answer: D
Correct answer: 3NF
Third normal form removes both partial and transitive dependencies and can always be reached without losing any functional dependency, which is why it is the normal form ordinarily aimed at. BCNF is stronger but may not be dependency preserving, and 4NF and 5NF address problems that arise less often.
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