Class notes introduction to DBMS (BCA501) Introduction to Database Management Systems, ISBN: 9780070591196

UNIT-4
Relational Data Model
What is Relational Model?
Relational Model (RM) represents the database as a collection of
relations. A relation is nothing but a table of values. Every row in
the table represents a collection of related data values. These rows in
the table denote a real-world entity or relationship.
The table name and column names are helpful to interpret the
meaning of values in each row. The data are represented as a set of
relations. In the relational model, data are stored as tables. However,
the physical storage of the data is independent of the way the data
are logically organized.
Some popular Relational Database management systems are:
● DB2 and Informix Dynamic Server – IBM
● Oracle and RDB – Oracle
● SQL Server and Access – Microsoft

Relational Model Concepts in DBMS
1. Attribute: Each column in a Table. Attributes are the
properties which define a relation. e.g., Student_Rollno,
NAME,etc.
2. Tables – In the Relational model the, relations are saved in the
table format. It is stored along with its entities. A table has two
properties rows and columns. Rows represent records and
columns represent attributes.
3. Tuple – It is nothing but a single row of a table, which
contains a single record.

, 4. Relation Schema: A relation schema represents the name of
the relation with its attributes.
5. Degree: The total number of attributes which in the relation is
called the degree of the relation.
6. Cardinality: Total number of rows present in the Table.
7. Column: The column represents the set of values for a specific
attribute.
8. Relation instance – Relation instance is a finite set of tuples in
the RDBMS system. Relation instances never have duplicate
tuples.
9. Relation key – Every row has one, two or multiple attributes,
which is called relation key.
10. Attribute domain – Every attribute has some pre-defined
value and scope which is known as attribute domain




Relational Integrity Constraints
Relational Integrity constraints in DBMS are referred to conditions
which must be present for a valid relation. These Relational

, constraints in DBMS are derived from the rules in the mini-world
that the database represents.
There are many types of Integrity Constraints in DBMS. Constraints
on the Relational database management system is mostly divided
into three main categories are:
1. Domain Constraints
2. Key Constraints
3. Referential Integrity Constraints

Domain Constraints
Domain constraints can be violated if an attribute value is not
appearing in the corresponding domain or it is not of the appropriate
data type.
Domain constraints specify that within each tuple, and the value of
each attribute must be unique. This is specified as data types which
include standard data types integers, real numbers, characters,
Booleans, variable length strings, etc.
Example:
Create DOMAIN CustomerName
CHECK (value not NULL)



The example shown demonstrates creating a domain constraint such
that CustomerName is not NULL

Key Constraints
An attribute that can uniquely identify a tuple in a relation is called
the key of the table. The value of the attribute for different tuples in
the relation has to be unique.