Computer ScienceCBSE Class 12 · Database Concepts

Relational Data Model: Relation, Attribute, Tuple, Domain, Degree and Cardinality (Class 12 Computer Science)

Updated 17 October 2026 · Fact-checked

In the relational model, data is stored in relations (tables). Each column is an attribute, each row is a tuple, and the set of allowed values of an attribute is its domain. The degree of a relation is the number of attributes, and the cardinality is the number of tuples.

Understand Relational Model: Relation, Attribute, Tuple, Domain, Degree, Cardinality

The relational data model stores data in relations. A relation looks like a table.

Relation: a table with rows and columns.
Attribute: a column of the relation; it names one property, such as Name.
Tuple: a row of the relation; it holds one record, such as one student.
Domain: the set of values that an attribute may take. For Class the domain may be the set of values 12A, 12B, 12C.
Degree: the number of attributes (columns).
Cardinality: the number of tuples (rows).

Example. The STUDENT relation of the chapter:

RollNo	Name	Class	Phone	HouseID
1	Asha	12A	98100 11111	H1
2	Ravi	12B	98100 22222	H2
3	Meena	12A	98100 33333	H1
4	Joy	12C	NULL	H3

Its degree is 5 (RollNo, Name, Class, Phone, HouseID) and its cardinality is 4. The tuple (4, Joy, 12C, NULL, H3) has a NULL, which means the phone value is unknown or absent.

Properties of a relation.

Each attribute has a unique name within the relation.
All values in a column come from the same domain.
Every cell holds a single (atomic) value, never a list.
No two tuples are identical (every tuple is different).
The order of tuples and attributes does not matter.

Changes. Adding a row raises the cardinality by 1; deleting a row lowers it. Adding a column (ALTER TABLE) raises the degree; dropping a column lowers it. Remember: degree is about columns, cardinality about rows.

Relational Model: Relation, Attribute, Tuple, Domain, Degree, Cardinality: key facts

Terms: Relation table
Attribute column
Tuple row
Domain set of allowed values of an attribute; Row = record, column = field.
Degree and cardinality: Degree: number of attributes (columns) | Cardinality: number of tuples (rows); Degree is about columns, cardinality about rows.
Properties of a relation: Unique attribute names
Single atomic value per cell
Values in a column from one domain
No identical tuples
Order of rows and columns not important; Used to check if a table is a valid relation.
Effect of changes: INSERT adds 1 to cardinality
DELETE reduces cardinality
ADD COLUMN adds 1 to degree
DROP COLUMN reduces degree; UPDATE changes neither.

Relation	table
Attribute	column
Tuple	row
Domain	set of allowed values of an attribute

How to answer Relational Model: Relation, Attribute, Tuple, Domain, Degree, Cardinality questions

Use this routine for degree and cardinality questions.

1Count the columns for the degree; do not count the heading row as a tuple.
2Count the rows (tuples) for the cardinality.
3Apply each change in order: rows for INSERT or DELETE, columns for ADD or DROP; UPDATE changes only values.
4Write both numbers with their names: degree = ..., cardinality = ....
5For a valid-relation question test each property: atomic values, no duplicate tuples, unique attribute names.

Relational Model: Relation, Attribute, Tuple, Domain, Degree, Cardinality in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

A class list as a relation

Suppose a teacher keeps a class list with columns RollNo, Name and Section for 30 students.

State the degree and the cardinality.

Try it first, then show the solutionSolution

Three columns give degree 3.
Thirty rows give cardinality 30.

Answer: Degree 3, cardinality 30

Memory hook: Degree counts the columns; cardinality counts the cards (rows).

A cell with two phone numbers

Suppose a table stores the Phone of a student as "98100 11111, 98100 22222" in one cell.

Why does this break a rule of the relational model?

Try it first, then show the solutionSolution

Every cell must hold a single, atomic value.
Two numbers in one cell violate that; use two rows or two columns.

Answer: It violates the atomic-value property.

Memory hook: One box, one item.

Tricks to remember Relational Model: Relation, Attribute, Tuple, Domain, Degree, Cardinality

Short memory aids. Say each one aloud once, then use it on a question the same day.

Cardinality = count of Cards (rows)
Think of cards in a card index: the number of cards is the cardinality.
Use it when: Telling degree and cardinality apart.
Degree = Down the Page
Degree is the number of columns that run down the page.
Use it when: Remembering which is which.
Row = tuple = record
Tuple, row and record mean the same thing.
Use it when: Terminology questions.
One cell, one value
Every cell holds a single value, never a list.
Use it when: Valid relation tests.

Relational Model: Relation, Attribute, Tuple, Domain, Degree, Cardinality: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Degree · 1 mark · MCQBoard level

The number of attributes in a relation is called its:
(a) cardinality (b) degree (c) domain (d) tuple

Try it first, then show the solutionSolution

Attributes are columns; the count of columns is the degree.

Answer: (b) degree

Example 2: Define terms · 2 marks · Short answerBoard level

Define attribute and tuple with reference to a relation.

Try it first, then show the solutionSolution

An attribute is a column of a relation; it names a property of the data. (1 mark)
A tuple is a row of a relation; it stores one record. (1 mark)

Answer: Attribute: column. Tuple: row.

Example 3: Compute degree and cardinality · 3 marks · Short answerHarder board level

STUDENT has 5 attributes and 4 tuples; HOUSE has 3 attributes and 3 tuples. A column Email is added to STUDENT, Joy's row is deleted and two new rows are inserted. Find the degree and cardinality of STUDENT now.

Try it first, then show the solutionSolution

Adding Email raises the degree from 5 to 6. (1 mark)
Deleting a row: cardinality 4 - 1 = 3; inserting two rows: 3 + 2 = 5. (1.5 marks)
HOUSE is unchanged. STUDENT: degree 6, cardinality 5. (0.5 mark)

Answer: Degree 6, cardinality 5

Example 4: Is it a relation? · 3 marks · Short answerHarder board level

A table has these rows for (RollNo, Name, Phones): (1, Asha, "111, 222"), (2, Ravi, "333"), (2, Ravi, "333"). State two properties of a relation that it violates.

Try it first, then show the solutionSolution

The Phones cell of the first row holds two values, so the atomic-value property is violated. (1.5 marks)
The second and third rows are identical, so the no-duplicate-tuples property is violated. (1.5 marks)

Answer: Atomic values and no duplicate tuples are violated.

Example 5: Case: library table · 4 marks · Case-basedHOTS / competency

Suppose a library keeps the relation BOOK(ISBN, Title, Author, Price, Copies) with 6 tuples.
(i) Write its degree and cardinality. (1 mark)
(ii) The library adds a column Shelf and 2 new books. Write the new degree and cardinality. (1 mark)
(iii) The price of one book is changed by an UPDATE. How do the degree and cardinality change? (1 mark)
(iv) Name the domain that is suitable for Copies. (1 mark)

Try it first, then show the solutionSolution

(i) Degree 5, cardinality 6.
(ii) Degree 5 + 1 = 6; cardinality 6 + 2 = 8.
(iii) Neither changes; UPDATE alters only a value.
(iv) Whole numbers, zero or more (non-negative integers).

Answer: (i) 5, 6 (ii) 6, 8 (iii) No change (iv) Non-negative integers

Where students lose marks in Relational Model: Relation, Attribute, Tuple, Domain, Degree, Cardinality

The slips examiners see most often, and what to write instead.

Mistake: Counting the heading row as a tuple
The first row shows attribute names; it is not a tuple.
Wrong working
Cardinality of STUDENT = 5
Right working
Cardinality of STUDENT = 4
Do this: Count only data rows.
Usually costs: 1 mark
Mistake: Interchanging degree and cardinality
Degree is columns; cardinality is rows.
Wrong working
STUDENT: degree 4, cardinality 5
Right working
STUDENT: degree 5, cardinality 4
Do this: Write the meaning before the number.
Usually costs: 1 mark
Mistake: Saying UPDATE changes the cardinality
UPDATE alters values in existing rows; no row is added or removed.
Wrong working
After UPDATE the cardinality increases by 1
Right working
Cardinality is unchanged
Do this: Only INSERT and DELETE change the row count.
Usually costs: 1 mark

Exam tips

Count the data rows only for cardinality, and all the columns for degree.
Show the arithmetic of sequences of changes in two lines.
Use the word tuple in definitions; row is accepted as the explanation.
In valid-relation questions name the exact property violated.
NULL is not a value like zero; it marks absent or unknown data.

Practice questions on Relational Model: Relation, Attribute, Tuple, Domain, Degree, Cardinality

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The number of tuples in a relation is called its:
(a) degree (b) cardinality (c) domain (d) attribute
Hint
Tuples are rows.
Answer
(b) cardinality
Q2 · 1 mark · Very short answerBoard level
What is a domain?
Hint
The allowed values of an attribute.
Answer
The set of values that an attribute may take.
Q3 · 2 marks · Short answerHarder board level
A relation ORDERS has degree 5 and cardinality 9. Three rows are inserted, two rows are deleted and one column is added. Find the new degree and cardinality.
Hint
Rows change cardinality; columns change degree.
Answer
Cardinality: 9 + 3 - 2 = 10. Degree: 5 + 1 = 6.
Q4 · 1 mark · Assertion-reasonHarder board level
Assertion (A): The order of tuples in a relation does not matter.
Reason (R): Tuples are identified by their values, not by their position.
(a) Both A and R are true and R is the correct explanation of A. (b) Both A and R are true but R is not the correct explanation of A. (c) A is true but R is false. (d) A is false but R is true.
Hint
Is there a "first row" in a relation?
Answer
(a) Both are true and R explains A.
Q5 · 3 marks · Short answerHOTS / competency
Suppose a relation EMP has degree 6 and cardinality 5. A student says that adding a new employee changes the degree to 7. Is she right? Find the correct values after adding two employees and one attribute.
Hint
Which count changes when a row is added?
Answer
No. A new employee is a new row, so the cardinality rises, not the degree. After two employees and one attribute: cardinality 5 + 2 = 7, degree 6 + 1 = 7.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is a tuple?Show answer
A row of a relation.
2.What is an attribute?Show answer
A column of a relation.
3.What is degree?Show answer
The number of attributes.
4.What is cardinality?Show answer
The number of tuples.
5.What is a domain?Show answer
The set of values allowed for an attribute.
6.Can a cell hold two values in a relation?Show answer
No; every cell is atomic.

Relational Model: Relation, Attribute, Tuple, Domain, Degree, Cardinality: frequently asked questions

What is the difference between degree and cardinality?

Degree is the number of attributes (columns) of a relation; cardinality is the number of tuples (rows).

What is a tuple in a database?

A tuple is a row of a relation. It stores one record, with one value for each attribute.

Does the order of rows matter in a relation?

No. The order of tuples and the order of attributes are not important; each tuple is identified by its values.

What is NULL in a relation?

NULL means a value is missing or unknown. It is not zero and not an empty string.