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DBMS Concepts And Logical Interview Questions

Below are few interview questions concerned with DBMS. These questions will test your understanding of concepts revolving around DBMS.

Question 1

In context of DBMS and its utilizing programs how you can explain the difference between Data and Information ?

Answer 1

Data can be considered as raw facts while information can be said as processed data conveying some meaning.

DBMS store data subject to certain constraints that maintain the integrity while utilizing programs derive information out of this data through queries issued by them.

Question 2

What is called metadata in context of DBMS ? Give a simple example.

Answer 2

Any data that gives information describing the database objects can be said as metadata. For example consider a database D with tables T1 and T2. Now if a third table TM stores the names and data types of columns in T1 and T2, then TM is said to contain metadata i.e data about data. Note : Generally all databases will have metadata storage about underlying databases, the structures within them etc. Metadata can also be user defined as in our example.

Question 3

What would happen if there is no rollback mechanism (undo mechanism) in databases. Tell with an example ?

Answer 3

Consider a bank transaction. Consider a table TBALANCE storing current balances in accounts and other table TINTEREST storing the calculated interest rate for any account balance at given point in time. If a person visits ATM and withdraws some amount from his account this data need to be reflected in both these tables. If the current balance is deducted from TBALANCE but if there is some technical problem that prevents the interest rate correction in TINTEREST then the entire transaction is invalid.

In this case the ATM should not deliver the cash. Also the data update in TBALANCE has to be rolled back to the previous value so that he can try again from start. If there is no rollback mechanism, the data integrity will be lost which will result in a conflict between balance and interest rate.

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