Relational Model

by E-Computer Concepts October 16, 2019 at 10:11 am

The Relational Model was a huge step forward, as it allowed files to be related by means of a common field. In order to relate any two files, they simply need to have a common field, which makes the model extremely flexible.

Relational Database Terminology

TermMeaning
RelationA table
TupleA row or a record
in a relation
AttributeA field or a column
in a relation
Cardinality
of a relation
The number of
tuples in a relation
Degree of a
relation
The number of
attribute on a
relation.
Domain of an
attribute
The set of all
values that can be
taken by the
attribute.
Primary Key
of a relation
An attribute or a
combination of
attributes that
uniquely defines
each tuple in a
relation.
Foreign KeyAn attribute or a
combination of
attributes in one
relation R1 which
indicates the
relationship of
R1 with another
relation R2.

Properties of Relations

No Duplicate Tuples

A relation can’t contain two or more tuples which have the same values for all the attributes. i.e., in any relation, every row is unique.

Tuples are unordered

The order of row in a relation is immaterial.

Attributes are unordered

The order of columns in a relation is immaterial.

Attribute Value are Atomic

Each tuple contains exactly one value for each attribute.

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