DBMS and SQL (OLD) - Test Papers 01

 CBSE TEST PAPER-01

Class-12 Computer Science(Database Concepts)

General Instruction: -

  • All question are compulsory.
  • Question No. 1 to 10 carries Two marks.
  1. What is a database? What are its advantages?
  2. What do you mean by data abstraction? What are the different levels of abstraction?
  3. What do you mean by data independence?
  4. Write a short note on Relational Model.
  5. Differentiate between degree and cardinality.
  6. Define Primary Key and Foreign Key.
  7. What do you mean by data redundancy?
  8. What is a view?
  9. Differentiate between Candidate Key and Alternate Key    .
  10. Observe the table ‘Club’ given below:

    Member_id

    Member_Name

    Address

    Age

    Fee

    M001

    Sumit

    Dewas

    20

    2000

    M002

    Nisha

    Indore

    22

    3500

    M003

    Sachin

    Bhopal

    21

    2100

    i) What is the cardinality and degree of the above-given table?
    ii) If a new column contact_no has been added and two more members have joined the club then how these changes will affect the degree and cardinality of the above-given table.

CBSE TEST PAPER-01
Class-12 Computer Science(Database Concepts)
[Answers]

  1. An organized collection of relational data is called a database.
    Advantages:
    Controlled data redundancy
    Reduced data inconsistency
    Improved data integrity
    Privacy and security
    Improved backup and recovery system
    Sharing of data
  2. A major purpose of a database system is to provide the users only that much information that is required for them. Data abstraction means the system does not disclose all the details of data, rather it hides certain details of how the data is stored and maintained.
    Different levels of abstraction are
    i. Internal Level (Physical Level): This level describes how the data are actually stored in the storage medium. At this level, complex low-level data structures are described in details. Eg. RollNo is in Byte(4), offset = 34.
    ii. Conceptual Level: It describes what data are actually stored in the database. It also describes the relationships existing among data. Eg. ItemCode is in Numeric(5).
    iii. External Level (View Level – Logical Level): This is the level closest to the users. It is concerned with the way in which the data are viewed by individual users. Most of the users of the database are not concerned with all the information contained in the database. Eg. View 1 contains RollNo, Name, DOB.
  3. The ability to modify a scheme definition in one level without affecting a scheme definition in the next higher level is called Data Independence.
  4. The relational model was propounded by E.F. Codd of the IBM and has since been acknowledged as a very important concept in DBMS. In this mode, the data is organized in the form of tables called relations. Each relation has tuples(rows in the table) and attributes(columns in the table).
  5. Degree : The number of attributes in a relation determine the degree of a relation.
    Cardinality : The number of tuples in relation is called the Cardinality of the relation.
  6. Primary Key : It is a set of one or more attributes that can uniquely identify tuples within the relation.
    Alternate Key : A candidate key that is not the primary key is called an alternate key.
  7. Data redundancy means duplication of data. Duplicate data is stored at different locations that violates the integrity of database and causes wastage of storage space.
  8. A view is a virtual table that is used to display only specific data instead of the entire data stored in a table. The data is derived from one or more base tables.
  9. Candidate Key : All attributes combinations inside a relation that can serve as primary key are Candiadate keys as they are candidates for the Primary Key position.
    Foreign Key : A foreign key is a non key attribute whose value is derived from the primary key of another table.
  10. i) Cadinality: 3Degree: 5
    ii) Cadinality: 5 Degree: 6