Define Autonomy, Distribution and Heterogeneity Discuss views in centralized DBMS.
Autonomy: It indicates the distribution of control of the database system and the degree to which each constituent DBMS can operate independently.
Distribution : It states the physical distribution of data across the different sites.
Heterogeneity: It refers to the uniformity or dissimilarity of the data models, system components and databases.
Discuss views in centralized DBMS:
View is a relation that is derived from a base relation via a query. It can involve selection, projection, aggregate functions, etc.
Example : The view of project manager derived from relation PROJECT (PNO, PTYPE, PCORDINATOR ), can be defined by the following SQL query:
PDATA
PNO PTYPE
P1 DATABASE APPLICATION
P12 BANK PROJECT
P17 MEDICAL PROJECT
P21 MECHANICAL
Solution:
CREATE VIEW PDATA (PNO, PCORDINATOR)
AS SELECT PNO, PCORDINATOR
FROM PROJECT
WHERE PCORDINATOR = "RUPALI"
The result of the query defining the view is not produced.
Example : "Find the names of all the system analysts with their project number and Responsibility ?"
Solution: This ESP, involves the view SYSAN and the relation ASG(ENO, PNO. REC DUR)
View Updates
Updatable view:
CREATE VIEW SYSAN(ENO,ENAME)
AS SELECT ENO,ENAME
FROM EMP
WHERE TITLE="Syst. Anal."
Non-updatable view:
CREATE VIEW EG(ENAME,RESP)
AS SELECT ENAME,RESP
FROM EMP, ASG
WHERE EMP.ENO=ASG.ENO
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