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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.
Define Deadlock detection If a system does not employ a few protocols that make sure deadlock freedom, after that a detection and recovery scheme should be used. An algorithm
1.Why we need data mining? Give an example to illustrate your answer. 2. Why data mining is considered as "misleading name"? 3. Distinguish the difference between database an
(1) Insert into PERSON Violated constraint: - Key constraint Reason: - Primary key 1 already exists in PERSON. Dealing: - DBMS could ask the user to provide valid PER
Having clause This clause is used for producing conditions on grouped information. Example: Find maximum salary and department number of those departments where maxim
Spanned and unspanned organisation? Spanned and unspanned organization: If records are not permited to cross block boundaries then the organisation is called unspanned record
What is Information System?
read-set(T) : Each data items that are read by a transaction T Timestamps : for all transaction T, the start-time and the end time are reserved for all the three phases.
Define lock? Lock is the most common used to execute the requirement is to permit a transaction to access a data item only if it is currently holding a lock on that item.
What is bucket overflow and how bucket overflow is handled through Over Flow Chaining or Closed Hashing? Ans: Bucket: unit of storage holding records. Bucket is a disk block
What are the advantages and disadvantages of merging an association into a class? Advantages: i) Less number of tables ii) Faster performance due to the fewer tables
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