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Briefly describe concurrency execution?
Lock - based protocols
Locks
There are several modes in which a data item may be locked in this section we restrict our attention to two modes
Ø Shared
Ø Exclusive
T1 : lock - x(B );
read(B);
B:=B-50;
write(B);
unlock(B);
Lock-x(A);
read(A);
A:=A+50;
write(A);
unlock(A).
What is assertion? Mention the forms available. An assertion is a predicate expressing a condition that we wish the database always to satisfy. Domain integrity constraints.
Q. Define a weak entity set and its identifying relationship. List the necessary conditions for a meaningful identifying relationship set of a weak entity set. Entity is a t
State the definition of association An association is a structural relationship which specifies that objects of one thing are connected with objects of another. In UML, asso
Explain retrieval in QBE? Retrieval in QBE : A "GUI" for expressing queries. Based on the Domain Relational Calculus (DRC) Actually invented before GUIs. Very co
Explain the term- Query. Queries are used to repossess and show specific records in a table. They can also be used to show specific fields of specific records, which meet the co
Aggregate functions Some of these functions are min, count, max, and avg. These functions help in getting consolidated information from a set of tuples. Example:
A relation instance indicates as r is a collection of tuples for a given relational schema at a exact point of time. A relation state r of the relation schema R (A 1 ,A 2 ,.....
what is attribute is attribute inheritance in dbms?
Benefits of heap files 1. This is a easy file Organisation method. 2. Insertion is somehow capable. 3. Good for bulk-loading data into a table. 4. Best if file
What is an ER diagram? Why is it used in Database management system (DBMS)?
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