1. What is DML (Data Manipulation Language)?

This language that enable user to access or manipulate data as organised by appropriate data model.

•  Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.
•  Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.

2. How does Tuple-oriented relational calculus differ from domain-oriented relational calculus

The tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values are tuples of that relation. E.g. QUEL

The domain-oriented calculus has domain variables i.e., variables that range over the underlying domains instead of over relation. E.g. ILL, DEDUCE.

3. Disadvantage in File Processing System

•  Data redundancy & inconsistency.
•  Difficult in accessing data.
•  Data isolation.
•  Data integrity.
•  Concurrent access is not possible.
•  Security Problems.

4. What is Object Oriented model?

This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.

5. What do you mean by Correlated subquery?

Subqueries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery.

A correlated subquery can be easily identified if it contains any references to the parent subquery columns in its WHERE clause. Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery.

Example :     Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)

6. What is meant by query optimization?

The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.

7. What is Lossless join property?

It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.

8. What is Set-at-a-time or Set-oriented?

The High level or Non-procedural DML can specify and retrieve many records in a single DML statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.

9. What is 1 NF (Normal Form)?

The domain of attribute must include only atomic (simple, indivisible) values.

10. Describe the three levels of data abstraction?

The are three levels of abstraction:

Physical level : The lowest level of abstraction describes how data are stored.

Logical level : The next higher level of abstraction, describes what data are stored in database and what relationship among those data.

View level : The highest level of abstraction describes only part of entire database.