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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.
(a) Explain the three types of potential mistake which could occur if concurrency control is not properly enforced in the database system. Support your answer with appropriate ex
Use a Set operator to create a list of academics who have written or co-written less than 5 papers and also have greater than 3 interests. List their academic number in the output.
Create an index for the table Client, field CLIENT_NO of Q ? Command: CREATE INDEX client_client_no ON client(client_no);
Define a property that is not a property of transactions? Ans: Concurrency is not a property of transactions
Explain the term High level DML? High level DML A high-level or non-procedural DML permit the user to specify what data is needed without specifying how it is to be acquired.
Exclusive lock It is asked for by a transaction on a data item that it wants to update. No other transaction can put either a shared lock or an exclusive lock on a dat
Define the following constraints for the table client. (i) BAL_DUE must be at least 1000. (ii) NAME is a unique key. (i)ALTER TABLE CLIENT ADD CONSTRAINT CLIENT_BAL_DUE_C1
what is natural join?
Explain how the associations are implemented as classes. A general approach in this case is to transform an association class into a simple class linked to two original classes
how can apply joins on table
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