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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.
Lossless-Join Decomposition Let us show an intuitive decomposition of a relation. We require a better basis for deciding decompositions since intuition may not always be r
Every simple attribute of an entity type have a possible set of values that can be attached to it. This is known as the domain of an attribute. An attribute cannot have a value out
During the deletion of a tuple two cases can happen: Deletion of tuple in relation having the foreign key: In this type of case simply delete the desired tuple. For example, in
Saving Derived Attributes to Avoid Re-computation As discussed, "redundancy means duplication of exact data". But, if multiple copies of same data are present in the system,
1.Suppose you are given a dataset that consists of a random sample of tasters, on which the following variables were obtained: (y) Zpref = taste preference for green beans store
Describe analysis of access paths To describe analysis of access paths, consider an example of the design of a company's employee skills database. A part of the object model fr
object oriented database
In an E-R diagram how attributes are represented ? In an E-R diagram attributes are represented in a ellipse.
what do you understand by enhanced entity-relationship
Multilevel Indexing Scheme Consider the indexing scheme where the address of the block is consider in the index for each record, for a little file, this index would be little a
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