1. Subject Name Code Credit Hours
Database System COMP 219 3
Chapter IV

2. Subject Name Code Credit Hours
Database System COMP 219 3
Data Models
• A collection of tools for describing
– Data
– Data relationships
– Data semantics
– Data constraints
• Relational model
• Entity-Relationship data model (mainly for database design)
• Object-based data models (Object-oriented and Object-relational)
• Semistructured data model (XML)
• Other older models:
– Network model
– Hierarchical model

3. Subject Name Code Credit Hours
Database System COMP 219 3
Data Models
• A collection of Conceptual tools for describing
– Data
– Data relationships
– Data semantics
– Data constraints
• Different data Models
• - Relational model
- Entity-Relationship data model (Conceptual Model-mainly for database design)
- Object-based data models (Object-oriented and Object-relational)
- Semi structured data model (XML)
• Other older models:
– Network model
– Hierarchical model
A Data model is a set of concepts that can be used to
describe the structure of the db.

4. Subject Name Code Credit Hours
Database System COMP 219 3
Entity-Relationship data model
• It is a high level conceptual data model that describes the structure of db
in terms of entities, relationship among entities & constraints on them..
• Basic Concepts of E-R Model:
- Entity
- Entity Set
- Attributes
- Relationship
- Relationship set
- Identifying Relationship
I

5. Subject Name Code Credit Hours
Database System COMP 219 3
Entity-Relationship data model
• Entity:
-It is a an object that exists in the real world.
• Example:
- Person, Employee, Car, Home etc..
Object with conceptual Existence
- Account, loan, job etc…

6. Subject Name Code Credit Hours
Database System COMP 219 3
Entity-Relationship data model
• Entity Set:
- A set of entities of the same type.
• Attributes:
- A set of properties that describe an
entity.

7. Subject Name Code Credit Hours
Database System COMP 219 3
• Types of Attributes:
• Simple (or) atomic vs. Composite:
• - An attribute which cant be sub divided. (Eg.Age)
• - An attribute which can be divided into sub parts is called
• as composite attribute.
e.g.. Address- Apartment no.
- Street
- Place
- City
- District
Single Valued vs. Multivalued:
• -An attribute having only one value (e.g.. Age,eid,sno)
• - An attribute having multiple values (e.g.. Deptlocat- A dept can be located in
several places)
Entity-Relationship data model

8. Subject Name Code Credit Hours
Database System COMP 219 3
Entity-Relationship data model
• Stored Vs Derived
• - Stored attribute is one that has some value where as
derived attribute is a one where its value is derived from sa.
• -E.g.. SA-DOB
• DA- Age derived from DOB.
• Key Attribute:
• - An attribute which is used to uniquely identify records.
• E.g.. eid, sno, dno

9. Subject Name Code Credit Hours
Database System COMP 219 3
Entity-Relationship data model
• Relationship:
• - It is an association among several
entities. It specifies what type of relationship
exists between entities.

10. Subject Name Code Credit Hours
Database System COMP 219 3
• Relationship set:
• - It is a set of relationships of the same type.
Entity-Relationship data model
1 AA 1000
2 BB 2000
100 FFF 10000
1 AA AC
2 BB AD
100 FFF SD
Entity
E
N
TI
T
Y
S
E
T
DEPT. ENTITY TYPERelationship SetEmp.. ENTITY TYPE

11. Subject Name Code Credit Hours
Database System COMP 219 3
• Weak Entity Set:
• - No key attributes.
• Identifying Relationship:
• - The relationship associated with the weak
entity type
Entity-Relationship data model

12. Subject Name Code Credit Hours
Database System COMP 219 3
Constraints
• Two of the most important constraints are
• a. Mapping Constraints
• b. Participation constraints
»Participation constraints
Total Participation Partial Participation

13. Subject Name Code Credit Hours
Database System COMP 219 3
a. Mapping Cardinalities:
Mapping Cardinalities OR CARDINALITY RATIOS, EXPRESSS THE NUMBER OF
ENTITIES TO WHICH ANOTHER ENTITY CAN BE ASSOCIATED VIA A
RELATIONSHIPSET.
• Several types of Mapping Cardinalities. They are,
• a.i. One-to-One
• An entity in set A is associated with at most one entity in set B and
vice versa.
e1
e2
e3
d1
d2
d3
Employee Dept.Works for

14. Subject Name Code Credit Hours
Database System COMP 219 3
• a.i. One-to-many
• An entity in set A is associated with zero or more
no. of entities in set B and an entity in B is associated with
at most one entity in A.
a. Mapping Cardinalities:
e1
e2
e3
d1
d2
d3
Employee Dept.Works for

15. Subject Name Code Credit Hours
Database System COMP 219 3
a. Mapping Cardinalities:
 a.i. Many-to-One
 One or more no. of entities in set A is associated with at
most one entity in B. An entity in B can be associated with any no.
of entities in A.
e1
e2
e3
e4
d1
d2
d3
Employee Dept.Works for

16. Subject Name Code Credit Hours
Database System COMP 219 3
• a.i. Many-to-Many
• One or more no. of entities in set A
is associated with one or more no. of
entities in set B.
a. Mapping Cardinalities:
e1
e2
e3
e4
d1
d2
d3
Employee Dept.Works for

17. Subject Name Code Credit Hours
Database System COMP 219 3
• The participation of an entity set E in a relationship set R is
said to be total if every entity in E participates in atleast one
relationship in R.
b. Participation Constraints:
Total Participation
Partial Participation:
The participation of an entity set E in a relationship set R is said to be
partial if only a few of the entities in E participated in relationship in R.

18. Subject Name Code Credit Hours
Database System COMP 219 3
b. Participation Constraints:
• E.G..
Partial participation Total participation
Employee
Dept.
Manages