The normalization was first proposed by .
Answer: B
Correct answer: Codd
E. F. Codd proposed normalisation along with the relational model. Note the spelling of the name and that Boyce-Codd normal form, named jointly, came later.
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Employees in a company are each assigned their own office, i.e. for each employee there exists a unique office and for each office there exists a unique employee; This statement is an example of ____ type of relation.
Answer: A
Correct answer: 1:1
One employee to one office and one office to one employee is a one-to-one relationship. The test is to read the mapping in both directions: if either direction allows several, the relationship is one-to-many or many-to-many.
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DBMS helps achieve
Answer: C
Correct answer: Both A and B
Both follow from holding the data in one managed store: control of the data is centralised in the DBMS rather than scattered among programs, and because programs address the data through the DBMS they no longer depend on how it is stored.
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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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In an E-R, Y is the dominant entity and X is a subordinate entity. Then which of the following is incorrect :
Answer: C
Correct answer: Operationally, if X is deleted, so is Y.
X is the subordinate, so it depends on Y and not the other way round: deleting the dominant entity Y removes the subordinate X, but deleting X leaves Y untouched. The keyed statement reverses that dependence.
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The concept of mapping of ______ entity types is the concept in which the for each strong entity type E in the ER schema, create a relation R that includes all the simple attributes of E
Answer: A
Correct answer: Regular
A regular, or strong, entity type has its own key and maps directly to a relation containing its simple attributes. A weak entity has no key of its own and must borrow the key of its owner, so its mapping is a different rule.
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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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Cascading rollback is avoided in all protocol except
Answer: D
Correct answer: two-phase locking protocol
Cascading rollback happens when one transaction reads data written by another that later aborts. Strict two-phase locking prevents it by holding exclusive locks until commit, and validation-based protocols prevent it by writing only at commit. Plain two-phase locking releases locks as soon as its shrinking phase begins, so uncommitted data can be read and cascading rollback becomes possible.
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In an E-R diagram double lines indicate
Answer: A
Correct answer: Total participation
Double lines from an entity to a relationship mean total participation: every entity in the set must take part in the relationship. A single line means participation is partial.
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The _______ is a set of programs to use and / or modify this data.
Answer: A
Correct answer: DBMS
The DBMS is the set of programs through which data is defined, stored, retrieved and modified. The database is the data; the DBMS is the software that manages it.
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