What is Data Model ? Discuss the classifications of Data Model?

https://www.computersprofessor.com/2016/06/what-is-data-model-discuss.html
Data Model:
Model is an
abstraction of Reality. The reality may be a business system, an engineering
system or a Public system. Data modelling is an Abstraction of Data about
entities of any System. The structure of database system is, the concept of a
data model.
Classifications of Data
Models:
Data Models are classified
on the level at which it is being used and as well as the type of the data
model. Data models are classified into 4 types, such as:
1.
External View Data Model
2.
Conceptual Data Model
3.
Internal Data Model
4.
Physical Data Model
External Data Model:
The arrangement of all
files for the Proposal system in the entire organization is called Schema. It
is actually a schematic representation. A portion of the schema of a database
is known as Sub-Schema.
In external view data
model, we discuss the system in brief. Thus, in this data model, we plan the
hardware configurations and software requirements. We construct a data model by
describing the over all view of all schematic representation and it has no
effect on the Software and Hardware specifications at this level.
Conceptual Data Model:
The conceptual data model
is a consolidated or overall view of all the user views. It gives a
comprehensive view of the entire database. In this data model, the hardware as
well as software gets effected when you change the H/w or S/w requirements. The
most widely used conceptual data model in the database is with Entity
relationship diagrams, known as ER-Diagrams.
Internal Data Model:
After planning the
conceptual data model thoroughly, the next step is, the data model is mapped /
implemented into any one of the following three data models, viz.
1. HDM
2. NDM
3. RDM
Such data model is known
as Internal Data model. The internal data model requires to design and match
the Conceptual data model characteristics.
Hierarchical Data Model
(HDM):
This type of data model is based
on the Hierarchical relations in the form of a Tree structure, in which the
root setment is kept at the top and further branches at downwards.
Network Data Model
(NDM):
A data model consists the set of
files and pairwise associations between the files. Each conceptual data model
is almost just like a Network data model and this data model is further classcified
into 3 types, viz.
a) Simple Network Data Model
b) Complex Network Data Model
and
c) Limited Network Data
Model.
Relational Data Model:
This data model uses the
concept of relations to represent each and every file in the system. The
relations are having 2-dimensional tables, representing the data in the form of
Attributes(fields) and Tuples
(Rows/Records) in the system. It is the most popular data model because, it is
Simple to implement.
It has the terminology
which is similar to that of a Conceptual DM.
It uses a Primary Key and
Secondary keys concept to relate/ establish a relationship in between any two
or more files.
Physical Data Model:
The physical data model
operates at the lowest level of data abstraction., that is, describing the way
the data is stored, saved and retrieved on the storage medium such as Hard
disk, magnetic disks, magnetic tapes etc. It is thus the process of accessing
and manipulating data from the disks.