Define Autonomy, Distribution and Heterogeneity Discuss views in centralized DBMS.

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)

 

Define Autonomy, Distribution and Heterogeneity Discuss views in centralized DBMS.

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