DBMS-Data Model

Data model is a mechanism that provides data abstraction for database application. data modelling is used for representing entities of interest and their relationship in the database. data model of collection of conceptual tools for describing data, data relationship and attachment 1 and data constraints.

 

They are different data models of database:

 

Object based logical model

1. Entity relationship model

2 object oriented model

3 semantic data models

 

Record based logical model

1. relational model

2 network model

3 hierarchical model

 

Hierarchical data model

HDM uses the tree concept to represent data and relationship among data. the Lords of the tree are connected by pointer all links. the relationship between the entities represented by the structure of the resulting ordered tree. is one parent and 30 one or more child. the parent record type can have any number of children record type. every child node a single parent node. to record types in hierarchy tree at most one relationship between them and his relationship is that of one two one or one to many

hierarchical data model

 

Limitation of Hierarchical Data Model

1 Each hierarchical tree can have only one root record type and this record type doesn’t have a parent record type.

2. the root can have any number of child record types, each of which of can itself be a root of hierarchical tree.

3. which skeleton record type can have only one panel record type does a many-to-many relationship cannot be directly expressed between two record types.

4. deleting the record occurrence require Hollywood children record of currencies.

5.Each Child Record Type can have only one parent record type ,thus many to many relationships can not be directly expressed between two records

 

Network data model

To overcome the problems posed by hierarchical model the network data model is developed. which allows multiple parent child relationship. these relationships are known as sets In Network data model .IN network data model data are represented by collection of records and relationships among data are represent by Link. this model support one to many and many to many relationships.
Network Model
Relational data model

relational data model is the most widely used data model, the vast majority of current database system are based on relational model. relational model uses a collection of tables to represent both data and the relationship among those data. relational model is an example of record based model. which record type defines a fixed number of fields at the columns of the table corresponding to the attribute of the record type.

Relational key SVG

Object relational data model

the database management system similar to a relational database but with an object oriented database model, objects classes and inheritance supported in database schemas and in the query language. ladies and it supports extension of data model with custom data types and methods

 

Object-Oriented Model

 

The Entity relationship model

The Entity relationship data model is widely widely used data model and it provides a convenient graphical representation you data relationships and constraints. it consist of basic objects called entities and a relationships among these entities entity is nothing but an object.

 

each entities are described in a database by set of attributes. and a relationship is an association among several entities.

simple ER Diagram

ER diagram are used to represent logical structure of database graphically. it contain following components

Rectangles– It represents entity sets

Ellipses– it represents attributes

Diamonds– it represents relationship among entity sets

Lines -which link attributes to entity sets and entity sets to a relationships.