Data models can be record-based (hierarchical, network, relational), object-based (entity-relationship, semantic, functional, object-oriented), or physical (unifying frame memory). The entity-relationship model is a method to visualize data logically and independently of hardware. It facilitates database design by allowing specification of entity types, relationships between entities, and attributes of entities. The main concepts are entities, relationships between entities, and attributes of entities.

2. DATA MODELS
Data models can be
Record-based
Object-based
Physical
Record-based data models
Hierarchical model
 Network model
 Relational model
Object-based data models
 Entity-relationship
Semantic
Functional
Object-oriented
Physical data models
Unifying model
Frame memory model

3. E-R Model
A method of communication amongst different
designers, programmers and end-users who tend to view
the data.
A non-technical, standard and logical way of visualizing
data.
An informal description of what users want from their
database.
A detailed and precise description which can be
implemented in a DBMS.
It is independent of any particular database management
system and hardware platform.
Facilitate database design by allowing specification of an
enterprise schema.

4. E-R Model concepts
The three main semantic concepts are :
 Entities
 Relationships
 Attributes
 Constraints ( on all of the above concepts)
Entities
An entity is an ‘object’ ( building , toy), an event (
sale, competition), a place ,a person or a concept (Course
, Account).
Entity type or set and entity instance :
Is a set of entities of the same type that share the same
properties.
Each entity type is identified by a name and a list of
attributes.
A database contains many different entity types .

5. E-R Model concepts
An entity corresponds to a table not to a row.
A table row is an entity instance.
An entity occurrence is an uniquely identifiable object of an
entity type.
Relationship
Is an association among two or more entities.
Similar relationships are grouped into relationship sets.
The relationship name describes its function.
Relationships are described in
 Degree
 Connectivity
 Existence
 n-ary relationship

6. E-R Model concepts
Attribute
Domain
Sub domain
Attribute domain
Attribute can be
 Simple attribute
 Composite attribute
 Single-valued attribute(PID)
 Multi-valued attribute (skill)
 Derived attribute
 Identifier attribute