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Illustrate the statement 'Projection operation distributes over the union operation'. Give an example.
Ans: ΠL(E1 ∪ E2) = (ΠL(E1)) ∪ (ΠL(E2))
This says that result acquired by projecting on an attribute set A, after taking union of two relations is similar as union of two relations each of which is a projection of original relations on A.
What is a cascading update? Referential integrity constraints needs that foreign key values in one table correspond to primary key values in another. If the value of the primar
Discuss The difference between drop table R and delete from R. DROP TABLE command deletes all the records with the table definition. This command will automatically committed
List the requirements needed to design a trigger. The requirements are:- Specifying when a trigger is to be implemented. State the actions to be taken when the trigger im
draw er diagram using entities crop,employee,department,plot,cultivation plan,machinery,seed,fertilizer
PRINCIPLES OF DATABASE 1. State the following terms: a) Database b) Database Management System c) Entity d) Attribute e) Relationship 2. Discuss the Three Level Architecture
Implementation of association as an object Implement as a separate association object, independent of either class, as in Figure. An association object is a group of pairs
Question: One of the tasks a database management system must perform is to ensure that the data is still intact in the face of software and hardware failure. This task is known
What is persistency? Persistency ensures which data is stored and that after the object is no longer available (program stops running) the data will be available to other users
The First Normal Form (1NF) Let us first describe 1NF: Definition: A relation (table) is in 1NF if 1. There are no duplicate tuples or rows in the relation. 2.
Objectives After reading this unit you should be able to: Explain storage of databases on hard disks; Discuss the execution of various file Organisation techniques;
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