Relational Data Model
Final Subject Marking Structure
Method Marks Pass Mark Final Weightage
Course Works ( Assignments ) 100 50 50%
Final Exam 100 40 50%
What is Relational Model ?
• The relational model for database
management is a mathematical model for
describing the structure of data.
What is a Database Model ?
• A database model is a type of data model that
determines the logical structure of a database
and fundamentally determines in which
manner data can be stored, organized, and
manipulated.
History
• This was first introduced by Ted
Codd of IBM research in 1970.
Ted Codd
• After that subsequently
maintained and developed by
Chris Date and Hugh Darwen
among others.
Chris Date
Other Logical Data Models
• Hierarchical database model.
• Network Model.
• Object Model.
• Document Model.
• Star Schema.
Relational Model vs. Relational DBMS
• The relational model is concerned with what
is required, which separates it from concerns
of how the model will be implemented.
• Relational Model focuses on representing data
through relationship held between those data
items.
• Data is represented in the form of Tuples.
• The data in the Relational Model is queried /
manipulated using Relational Algebra.
Relational Model vs. Relational DBMS
• How is the concern of relational DBMS.
• Data from the Relational Data Model is
represented in the form of tables and rows.
• The data is queried using particular query
languages, commonly this is a language
known as SQL ( Sequential Query Language ).
Three Parts of Relational Model ?
1) Structural :
-Defines the core of the data and the
relationships involved.
2) Manipulative :
-Queries (Operations that retrieve
information) .
-Modifications (Operations that change the
database).
3) Constraints :
-Limitations ( Ex : valid ranges, values of data
to be included, etc… ).
Structural
• This is described using four terms.
1. Relation – A relation comprises a set of tuples.
2. Tuple – A tuple is a sequence of attributes ( Ex :
a row in the relation table ).
3. Attribute – An attribute is a named column in
the relation table.
4. Domain – The domain construct is important as
it identifies the type of an attribute.
Structural
Properties of Relations
• There are three important properties.
1. Name – This will help to identify the relation.
( Ex : Smith is a Student, etc… ).
2. Cardinality – Number of tuples ( data rows ) in
the relation.
3. Degree – The number of attributes in each tuple.
Domains
• The Domain of an attribute defines the set of
values which can apply to that attribute.
Ex: Years – 1950 … 2020
Person Names - String
Notations to Describe the Relational Schema
• There are two main ways. Those are,
1. Detailing the domains of the attribute.
2.
Notations to Describe the Relational Schema
• Primary Key – The attribute that uniquely
identifies one tuple in a relation from another.
• Candidate Key – Attribute that can act as
primary key. There can be many candidate
keys on one table. One is chosen as primary
key.
• Foreign Key – An attribute that represents a
relationship with another relation. It is a
primary key of one relation which is included
as an attribute in another relation.
Null Values
• Special value Null can occur in any attribute.
• Has ambiguous meaning.
Ex: for cousellorNo may mean, student
doesn’t have a counsellor or that the
counsellor isn’t known.
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