1. ER- MODEL & RELATIONAL
MODEL
Dr. Robin Mathur,
LPU

2. DATA MODEL
Slide 1-2
A collection of tools for describing
Data
Data relationships
Data semantics
Data constraints

3. ER MODEL
• The ER model defines the conceptual view of a
database. It works around real-world entities
and the associations among them. At view
level, the ER model is considered a good
option for designing databases.
Slide 1-3

4. E-R model stands for Entity Relationship model. ER Model is
used to model the logical view of the system from data
perspective which consists of these components: Entity, Entity
Type, Entity Set.
An Entity may be an object with a physical existence – a
particular person, car, house, or employee – or it may be an
object with a conceptual existence – a company, a job, or a
university course.
An Entity is an object of Entity Type and set of all entities is
called as entity set. e.g.; E1 is an entity having Entity Type
Student and set of all students is called Entity Set.
ER MODEL

5. Relational data model
• The relational model used the basic concept of a relation or
table.
• The columns or fields in the table identify the attributes such
as name, age ,etc A tuple or row contains all the data of a
single instance of the table
• In the relational model, every tuple must have a unique
identification or key based on the data.
• Relational model also includes concepts such as foreign keys,
which are primary keys in one relation that re kept in another
relation to allow for the joining of data.
Slide 1-5

6. Relational data model
• Relational Model was proposed by E.F. Codd
to model data in the form of relations or
tables. After designing the conceptual model
of Database using ER diagram, we need to
convert the conceptual model in the relational
model which can be implemented using any
RDMBS languages like Oracle SQL, MySQL etc.

7. Relational data model
Slide 1-7

9. Database Designing
E-R Model Constructs
• Entity instance - person, place, object, event, concept
(often corresponds to a row in a table)
• Attribute - property or characteristic of an entity type
(often corresponds to a field in a table)
• Relationship instance – link between entities
(corresponds to primary key-foreign key equivalencies
in related tables)
– Relationship type – category of relationship…link between
entity types

10. Sample
E-R
Diagram

11. Basic E-R Notation
Entity
symbols
Relationship
symbols
Attribute
symbols
A special
entity that is
also a
relationship

12. Basic E-R Notation

13. E-R Model Constructs: Entity Type
• Entity - person, place, object, event, concept

14. Example of a weak entity

15. E-R Model Constructs: Attributes
• Attribute: a property or characteristic of an entity type
that is of interest to the organization
• Simple versus Composite Attribute
– a simple attribute cannot be broken down into smaller
components, while a composite attribute can be
broken down into component parts
– Single-Valued versus Multivalued Attribute
• Stored versus Derived Attributes
– A stored attribute is one whose values are stored in the
database
– A derived attribute is one whose whose values can be
calculated from related stored attributes

16. A composite attribute
An attribute
broken into
component parts

17. Entity with a multivalued attribute (Skill)
and derived attribute (Years_Employed)
Multivalued:
an employee can have
more than one skill
Derived
from date employed and current date

18. Attribute that is both multivalued and composite
This is an
example of
time-stamping

19. E-R Model Constructs: Identifier or Key
• Identifier or Key
– an attribute (or combination of attributes) that
uniquely identifies individual instances of an entity
type
• Simple Key versus Composite Key
• Candidate Key - an attribute that could be a key
• Criteria for Selecting Identifiers
– Will not change in value
– Will not be null
– No intelligent identifiers (containing e.g. locations or
people that might change)
– Substitute new, simple keys for long, composite keys

20. Simple key attribute
The key is underlined

21. Composite key attribute
The key is composed
of two subparts

22. Relationships
• Relationship type (is a meaningful association between entity
types; is modeled as the diamond and lines between entity
types; can have attributes) vs. Instance
• Multiple Relationships
– more than one type of relationship between entities
• Degree of a relationship - number of entity types that
participate in it
– Unary (or Recursive) Relationship
– Binary Relationship
– Ternary Relationship
• Cardinality of Relationships
• Many-to-Many and Associative Entities (combination of
relationship and entity)
– All relationships involved are “many”
– Result has independent meaning
– One or more non-key attributes

23. Relationship type (Completes)

24. Degree of relationships
One entity
related to
another of
the same
entity type
Entities of
two different
types related
to each other
Entities of three
different types
related to each
other

25. Cardinality of Relationships
• One – to – One
– Each entity in the relationship will have exactly one related
entity
• One – to – Many
– An entity on one side of the relationship can have many
related entities, but an entity on the other side will have a
maximum of one related entity
• Many – to – Many
– Entities on both sides of the relationship can have many
related entities on the other side

26. Cardinality

27. Unary relationships

28. Binary relationships

29. Ternary relationships
Note: a relationship can have attributes of its own

30. Strong and weak entities
Strong entity Weak entity
Identifying relationship

31. Slide 1-31

32. SOME MCQS …