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Monday, July 23, 2012

Comparison between hierarchical model, network model and relational model

Data models, Data structures, Data manipulation, Data integrity comparison


 

When we move with the data models such as hierarchical model, network model, relational model we can identify number of difference in terms of data structures, Data manipulation and Data integrity.


 

Characteristic

Hierarchical model

Network model

Relational model


 

Data structure

When we go through the structure of

the hierarchical model we can identify that it used a method for storing data in a database that looks like a family tree with one root and a number of branches or subdivisions. That's why we can say that record types are organized in the form of a rooted tree. But in network model we can identify multiple branches emanating from one or more nodes. So some times it is like a like several trees which share branches. In relational model is that of a relation. Relation is a two-dimensional table. So the table can be used to represent some entity information or some relationship between them

Data structure

One to many or one to one relationships

Allowed the network model to support many to many relationships

One to One,
One to many, Many to many relationships

In hierarchical model only one-to-many or one-to-one relationships can be exist. But in network data model makes it possible to map many to many relationships In relational each record can have multiple parents and multiple child records. In effect, it supports many to many relationships

Data structure

Based on parent child relationship

A record can have many parents as well as many children.

Based on relational data structures


 

In hierarchical model relationship based in terms of parent child. So a child may only have one parent but a parent can have multiple children. But in network data model a record can have many parents as well as many children. Relational data model is based on relational data structures

Data manipulation

Does not provide an independent stand alone query interface

CODASYL (Conference on Data Systems Languages)

Relational databases are what brings many sources into a common query (such as SQL)

In relational database it use powerful operations such as SQL languages or query by example are used to manipulate data stored in the database But in hierarchical data model it does not
provide an independent stand alone query interface while network model uses CODASYL

Data manipulation

retrieve algorithms are complex and asymmetric

Retrieve algorithms are complex and symmetric

Retrieve algorithms are simple and symmetric

In hierarchical data model and network model retrieve algorithms are complex and symmetric But in relational data model retrieve algorithms are simple and symmetric

Data integrity

Cannot insert the information of a child who does not have any parent.

Does not suffer form any insertion anomaly.

Does not suffer from any insert anomaly.

In hierarchical data model we cannot insert the information of a child who does not have any parent. But in network model does not suffer form any insertion anomaly. relational model does not suffer from any insert anomaly

Data integrity

Multiple occurrences of child records which lead to problems of inconsistency during the update operation

Free from update anomalies.

Free form update anomalies

In network model it is free from update anomalies because there is only a single occurrence for each record set.In relational model it also free form update anomalies because it removes the redundancy of data by proper designing through normalization process. But in hierarchical model there are multiple occurrences of child records. which lead to problems of inconsistency during the update operation

Data intergirty

Deletion of parent results in deletion of child records

Free from delete anomalies

Free from delete anomalies

In hierarchical model it is based on parent child relationship and deletion of parent results in deletion of child records .But in network model and in relational model it is free from deletion anomalies. Because information is stored in different tables.

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