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One-to-one relationship:
For every 1:1 relationship type R in the ER diagram including two entities E1 and E2 we take one of entities (say E1) preferably with total participation and add primary key attribute of one more entity E2 as a foreign key attribute in the table of entity (E1). We will also have all the simple attributes of relationship type R in E1 if any.
For instance, the DEPARTMENT relationship has been extended to contain head-Id and attribute of the relationship. Please note we will maintain information in this table of only present head and Date from which s/he is the head.
There is one Head_of 1:1 relationship among FACULTY and DEPARTMENT. We select DEPARTMENT entity having total participation and add primary key attribute ID of FACULTY entity as a foreign key in DEPARTMENT entity named as Head_ID. Now the DEPARTMENT table will be as follows:
DEPARTMENT
D_NO
D_NAME
Head_ID
Date-from
Foreign Keys and NULL Let us take the relation: DEPT DEPT ID DNAME BUDGET D1 M
Create 1 experiment to demonstrate an aspect of query optimisation by using access-path structures (indexes), decomposition, or denormalisation. Once satisfied with your experiment
Write short notes on extension and intension? In any data model, it is significant to distinguish among the description of the database and the database itself the description
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Explain what is Aggregation ? Aggregation: This is used whenever we intend to show a relationship between an entity and the relationship. There is no provision for this in th
Synonyms It allows short names or alternative names for objects. Example : CREATE SYNONYM D30 FOR EMPD30; Now if we give command:
Design a database for an airline.The database must keep track of customers and their reservations,flights and their status, seat assignment on individual flights and, the schedule
Which are the two ways in which entities can participate in a relationship? Total and partial are the two ways in which entities can participate in a relationship
Example :; transfers transfer_amount from x's account to y's account ; Supposes x&y both accounts exist TRANSACTION (x, y, transfer_amount) Start transaction IF X AND Y
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