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Explain data independence ?
Data independence is the capacity to modify the schema at one stage of a database system without having to change the schema at the further level. The three-schema architecture permits the feature of data independence. Data independence occurs since while the schema is changed at a few level, the schema at the further level remains unchanged; only the mapping among the two levels is changed.
Having Clause with sub queries: First we have to recollect the GROUP BYclause. The following query searches the minimum salary in every department. SELECT DEPTNO, MIN (SAL)
What is a value? A data value is used for identity. This form of identity is used in relational systems.eg: The primary key value of a tuple recognize the tuple.
Making Common Behaviour Abstract Let us define abstraction "Abstraction means to focus on the necessary, inherent aspects of an entity and ignoring its accidental features". O
Relational Algebra is a set of basic operations used to influence the data in relational model. These operations allow the user to specify basic retrieval request. The result of re
What is meant by object-oriented data model? The object-oriented paradigm is based on encapsulation of data and code related to an object in to a one unit, whose contents are n
Update or Modify operation alters the existing values. If these operations alter the value that is the foreign key also, the only check need is the similar as that of the Insert op
Define weak and strong entity sets? Weak entity set: entity set that do not have key attribute of their own are known as weak entity sets. Strong entity set
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How does the system cope up with a record crash when recovery is going on after the first crash? Ans: In a system the undo and redo operations are needed to be idempotent to c
A set of possible data values is called? A set of possible data values is called as domain.
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