Definition are Network, Hierarchical and entity -relationship model

Definition are Network, Hierarchical and entity -relationship model

Network Model:-
The network Model data are represented by collection of records and relationships among data are represented by links.
Advantages of network Model:-
Simplicity:- The network Model is also conceptually simple and easy to design.
Ability to handle more relationship type:- The network Model can handle the one to many and many to many relationships.
Easy of data access:- Relationship is a set comprises of two type of records an owner record and a member record.
Data integrity:- In a network model no member can exist without an owner. A user must therefore first define the owner record and then the member record.
Data independence:- The network Model draws a clear line of demarcation between the programs and the complex physical storage details.
Database standard:- The standard devised by the DBTG (database Task Group of CODASYL Commtiee)form the basis of the network Model.
Disadvantage of network Model:-
 System complexity:-In network model data are accessed one record at a time.A user friendly database management system cannot be created using the network database model.
Lack of structural independence:-  Making structural modifications to the database is very difficult in the network database model as the access method is navigational.
Hierarchical Model:-
Hierarchical model is one of the oldest database model dating from late 1950s. The Hierarchical model is based on the assumption that a free structure is the most frequently occurring relationship.
Entity -relationship model:-
The main drawback of the Hierarchical model was that there were no standard for the hierarchical database model.The lack of a data manipulation language (DML) components made it difficult to use the database effectively.

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