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It defines that the tuple in one relation that refers to another relation must refer to an existing tuple in that relation. This constraint is states on two relations (not essentially distinct). It uses a concept of foreign key and has been dealt with in more factors in the next unit.
Example
In the example given above, the value of C^ in every R tuple is matching with the value of C# in some S tuple. If a tuple has values (A6, B2, and C4) is added then it is invalid as referenced relation S doesn't contain C4. Therefore, it will be a violation of referential integrity constraint.
Differance between internal and external schema? Internal and external schema: Internal Schema • Describes the physical storage structure • Uses a physical data model External
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The result of the UNION operation between R1 and R2 is a relation that includes? The result of the operation between R1 and R2 includes all the tuples of R1 and R2 which have c
what is cascading? what is rollback cascading? please explain in detail
What is recovery management component? Ensuring durability is the responsibility of a software component of the base system known as the recovery management component.
What is called mirroring? The simplest approach to introducing redundancy is to duplicate each disk. This method is called mirroring or shadowing.
normal forms
A relation has: Relational Schema Relation instance Relational Schema: A relational schema shows the relation's name, its attributes and the domain of every a
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