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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.
Data independence seems that "the application is independent of the access strategy and storage structure of data". In other words, the ability to change the schema definition in o
Chapter 10a review questions
Heap files (unordered file) Mostly these files are unordered files. It is the easiest and most basic type. These files having of randomly ordered records. The records will have
Explain the Cascadeless Schedule A cascadeless schedule is one in which for every pair of transactions Ti and Tj like that Tj reads a data item before written by Ti, the commit
#questiononsider the following relation: CAR_SALE =(CAR_ID,oPTION_TYPE, Option_listpreice, Sale_date, Option_discountedprice)..
Durability : This property necessitates that once a transaction has committed, the changes made by it be never lost because of subsequent failure. Thus, a transaction is also a bas
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Define Database layer? The database layer defines the data formats used in the database.
Why 'AS' clause is used in SQL ? 'As' clause is used for Rename operation. ‘AS' clause is used in SQL for rename operation. (e.g., SELECT ENO AS EMPLOYEE_NO FROM EMP)
Differance between Unordered and ordered file ? Unordered file do no has any sequence although ordered file has arranged in a few sequence and data are assigned in ordered form
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