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

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.