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Unrepeatable reads: Assume T7 reads X twice during its implementation. If it did not update X itself it could be very disturbing to see a dissimilar value of X in its next read. But this could occur if, among the two read operations, another transaction modifies X.
T7
T8
Assumed value of
X=2000
READ X
2000
UPDATE X
3000
Therefore, the inconsistent values are read and results of the transaction may be in fault.
Describe domain constraints. Domain constraints contain entity integrity and referential integrity. The domain is a set of values that might be assigned to an attribute. The en
What is conceptual model ? A conceptual model is a independent of both hardware and software.
What are the advantages of object oriented databases in comparison with others? Why it is still not widely used? Object oriented designs are coherent, efficient and less prone
In E-R diagram how generalization is represented? in E-R diagram generalization is represented by Triangle shape.
Shared lock or Read Lock It is requested by a transaction that needs to just read the value of data item. A shared lock on a data item does not permit an exclusive lock
Define null values. In some cases a certain entity may not have an applicable value for an attribute or if we do not know the value of an attribute for a certain entity. In the
In a relation, tuples are not inserted in any definite order. Ordering of tuples is not defined as a part of a relation definition. Though, records may be structured later accordin
What are the various states through which a transaction passes through in its lifetime? Briefly discuss all the events that causes transition from one state to another. Ans:
An entity type usually has an attribute whose values are distinct for every individual entity in the collection. Such an attribute is known as a key attribute and its values can be
Why is database design important?
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