NCERT solutions for Computer Science [English] Class 12 chapter 8 - Database Concepts [Latest edition]

Give the term for the following:

Collection of logically related records.

Give the term for the following:

DBMS creates a file that contains a description of the data stored in the database.

Give the term for the following:

Attribute that can uniquely identify the tuples in a relation.

Give the term for the following:

Special value that is stored when an actual data value is unknown for an attribute.

Give the term for the following:

An attribute that can uniquely identify tuples of the table but is not defined as the primary key of the table.

Give the term for the following:

Software that is used to create, manipulate and maintain a relational database.

Why foreign keys are allowed to have NULL values? Explain with an example.

Differentiate between Database state and database schema.

Differentiate between Primary key and foreign key.

Differentiate between the Degree and cardinality of a relation.

Compared to a file system, how does a database management system avoid redundancy in data through a database?

What are the limitations of the file systems that can be overcome by a relational DBMS?

A school has a rule that each student must participate in a sports activity. So each one should give only one preference for sports activity. Suppose there are five students in a class, each having a unique roll number. The class representative has prepared a list of sports preferences as shown below. Answer the following:

1. Roll no 24 may not be interested in sports. Can a NULL value be assigned to that student’s preference field?
2. Roll no 17 has given two preference sports. Which property of relational DBMC is violated here? Can we use any constraint or key in the relational DBMS to check against such violations, if any?
3. Kabaddi was not chosen by any student. Is it possible to have this tuple in the Sports Preferences relation?

In another class having 2 sections, the two respective class representatives have prepared 2 separate Sports Preferences tables, as shown below:

Sports preference of section 1 (arranged on roll number column)

Sports preference of section 2 (arranged on Sports name column, and column order is also different)

Are the states of both relations equivalent? Justify.

The school canteen wants to maintain records of items available in the school canteen and generate bills when students purchase any item from the canteen. The school wants to create a canteen database to keep track of items in the canteen and the items purchased by students. Design a database by answering the following questions:

1. To store each item name along with its price, what relation should be used? Decide appropriate attribute names along with their data type. Each item and its price should be stored only once. What restriction should be used while defining the relation?
2. In order to generate a bill, we should know the quantity of an item purchased. Should this information be in a new relation or a part of the previous relation? If a new relationship is required, decide the appropriate name and data type for attributes. Also, identify the appropriate primary key and foreign key so that the following two restrictions are satisfied:
   i) The same bill cannot be generated for different orders.
   ii) Bill can be generated only for available items in the canteen.
3. The school wants to find out how many calories students intake when they order an item. In which relation should the attribute ‘calories’ be stored?

An organisation wants to create a database EMPDEPENDENT to maintain the following details about its employees and their dependent.

EMPLOYEE(AadharNumber, Name, Address, Department, EmployeeID)
DEPENDENT(EmployeeID, DependentName, Relationship)

1. Name the attributes of EMPLOYEE, which can be used as candidate keys.
2. The company wants to retrieve details of the dependent of a particular employee. Name the tables and the key which are required to retrieve this detail.
3. What is the degree of EMPLOYEE and DEPENDENT relation?

School uniform is available at M/s Sheetal Private Limited. They have maintained SCHOOL_UNIFORM Database with two relations viz. UNIFORM and COST. The following figure shows the database schema and its state.

1. Can they insert the following tuples to the UNIFORM Relation? Give reasons in support of your answer.
   i) 7, Handkerchief, NULL
   ii) 4, Ribbon, Red
   iii) 8, NULL, White
2. Can they insert the following tuples to the COST Relation? Give reasons in support of your answer.
   i) 7, S, 0
   ii) 9, XL, 100

In a multiplex, movies are screened in different auditoriums. One movie can be shown in more than one auditorium. In order to maintain the record of movies, the multiplex maintains a relational database consisting of two relations viz. MOVIE and AUDI respectively as shown below:

Movie(Movie_ID, MovieName, ReleaseDate) Audi(AudiNo, Movie_ID, Seats, ScreenType, TicketPrice)

1. Is it correct to assign Movie_ID as the primary key in the MOVIE relation? If no, then suggest an appropriate primary key.
2. Is it correct to assign AudiNo as the primary key in the AUDI relation? If no, then suggest an appropriate primary key.
3. Is there any foreign key in any of these relations?

1. Name the primary key of each table.
2. Find foreign key(s) in table PROJECT-ASSIGNED.
3. Is there any alternate key in table STUDENT? Give justification for your answer.
4. Can a user assign duplicate value to the field RollNo of STUDENT table? Justify.