Data Models | DBMS

Concept of Data Models

Data model can be define as logical set of relationship describing behaviour and nature.

 

One data model can be distinguish from other on the basis of the way the relation ship among data is define and the way the database is conceptually(logically) define.

There are various data model that are choose as per the need of application.These all fall in three categories such as.

 

 

Physical Data Model

 

Physical data model are used to describe the behaviour of data at disk level.i.e the way the data and relation ship are maintain while starting on disk.These decide the way the DBMS is going to use secondary storage device for storing and accessing database.The commonly used physical data model are -

1. Unifying Model
2. Frame Memory

 

Logical Data Model

 

Logical models are used in describing data and its relationship at logical and view level.

 

Object Based Logical Model

 

Object based logical model emphasis the thought that every thing is an object having a set of attributes. Two different object posses the relationship among them and the relationship have direct impact over the attribute of object.

 

In this category there are two type 

1. Object Oriented Data Model:

Object oriented data model takes every thing as an object.This model introduce the concept of class that contains object having same type of values i.e same set of attributes name and same method.At any particular moment of time , object can be said to be the instance of class.Two or more object communicate each other by passing messages. 

 

 

2. ER Model (Entity Relationship Model):

 

ER-model is based on the thought that every thing that have physical properties or attribute is entity and every two entity can be distinguish from other through their own set of properties. Two or more entities possess relationship among each other.It is easy to specify integrity and security constraint in ER Diagram.

 

To represent ER diagram following symbols are used

1. Rectangle: To represent Entity.

2. Ellipse: To represent attributes.

3. Diamond: To represent relationship among entity set.

4. Lines: To show link between entity and relationship.

 

Example: 

 

 

Record Based Logical Model

This category of model also describe data at the logical and view levels.But in contrast to the object based object model they revolved around record of database with the help of values of record.

Record based data model does not represent the logical structure through instruction of programs. They have different set of languages that are involved in this model to establish relationship among defined schemata.

This category also have a wide range of data models some of the popular data models that falls in this category are:

1. Relational Model
2. Network Model
3. Hierarchical Model

Relational Model

It is the most popular among the various record based data models. In this data model proposed by codd, all data would be represented in tables made up of row and columns.Tables are given the name relation, the rows represent the record and the column represent the attribute or properties. In this model the data is handled on a conceptual rather than physical basis.

Hierarchical and Network Model

In Hierarchical model every child can have only one parents. While in network model every child can have more than one parent. Both use the concept of pointer for maintaining the relationship. In the case of relational data model relationship is maintained at the conceptual level.

Example:

Note:

How many number of record and what type of record are used ?

    ** If number of record is more and record is rare than we use Network Model.

    ** If number of record is less and relation are rare than we use Hierarchical Model.