05-07-2013, 04:22 PM
DATABASE MANAGEMENT SYSTEM 2 MARKS QUESTION ANSWERS
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1. Define DBMS?
A database management system is a collection of interrelated data and a set of programs to access those data’s.The collection of data is usally referred to as database.DBMs is hence a general-purpose software system that facilitates the processes of defining,constructing and manipulating databases for various applications.
2. Give the uses of DBMS?
The database systems are widely used in the following areas such as banking,airline reservation,universities,credit card transaction,telecommunication,finance,sales,manufacturing and human resources.
3. Discuss the three levels of abstraction?
Physical level
It is the lowest level of abstraction which describes how the data are actually stored in the database.
Logical level
It is the next higher level of abstraction which describes the actual data stored in the database and the interrelationship which exits among those data.
View level
It is the highest level of abstraction which describes only part of the entire database.
4. What is instance?
The collection of information stored in the database at a particular moment is called an instance of the database.
5.Define schema?
The overall design of the database is called the database schema.the schema may not change frequently.
6.What are the components of query processor ?
1. DDL interpreter
2. DML compiler
3. Query evaluation engine.
7.What are the functions of DBA?
1. Schema definition –writing DDL statements
2. Storage structure(i.e queue,stack etc)and access method (i.e sequential,random)definition.
3. Schema and physical organization,modification.
4. Granting of authorization for data access.
5. Routine maintenance.
8.Define data model?
Data model is defined as the collection of conceptual tools for describing data,data relationships,data semantics and consistency constraints.
9.Give the advantages of DBMS?
1. Improved use of data
2. Reduced data redundancy and inconsistency.
3. Enhanced data integrity.
4. Application data independence
5. Improved security
6. Reduced application development and maintenance cost
7. Increased access and availability of data and information.
10.Define relational models?
The relational model is based on simple concept of tables.the tables are called relations. Each row of data is equivalent to a record and is called a tuple. Each column of data is equivalent to a field and is called an attributes.
11.Define entity sets and relationship sets?
An entity is a ‘thing’ or ‘object’ in the real world that is distinguishable from all other objects. An entity set is a set of entities of the same type that share the same properties(attributes).
A relationship is an association among several entities. A relationship set is a set of relationship of same type.
12.Define domain of an attributes ?
The set of permitted values for each attribute in a relation is called as the domainof that attributes. That is only the data of same data type can be permitted to be the value of that attribute.
13.Define primary key?
An attribute which is used to identify a tuple with its unique values is called as primary key.
14.Define foreign key?
A relation schema say r1 may include among its attributes the primary key of another relation schema say r2. this attribute is called a foreign key of r1,referencing r2. the relation r1 is also called the referencing relation of the foreign key and r2 is called the referenced relation of the foreign key.
15.Differentiate super key and candidate key?
A super key is a set of one or more attributes that is used to identify a tuple. All the set of attributes in a relation can also be a super key.
Minimal number of super keys by which a tuple can be identified is called a candidate key.
16.Differentiate between the procedural and non procedural language?
In a procedural language the user give a set of instruction to perform a sequence of operations on the database to compute the desired result.
In a non procedural language the user describes the desired information without giving a specific procedure for obtaining that information.
17.Explain the cartesian product operation in relation algebra with an example?
Cartesian product is also known as cross product or cross join. the relations on which it is applied need not be union compactible. This operation is used to combine tuples from two relation in a combinational fashion.
18.Discuss relational calculus and mention its type?
Relational calculus is a non procedural query language in which there is no description of how to evaluate a query; thus a calculus specifies what is to be retrieved rather than how to retrieve it using only one expression