DataBase models are widely classified into 2 categories . They are
1. Object - Based Logical Models
The Object - based logical model can be defined as a collection of ideal tools for describing data , data relationships , and data constraints.
2. Record - Based Logical Models
The Record - based model describes the data structures and Access techniques of a DBMS .
They are 4 types of Record - Based Logical Models
1. File Management Systems [ FMS ]
The File Management Systems was the first method used to store data in a computerized database.The data item is stored sequentially in one large file.A particular relationship can not be drawn between the items other than thesequence in which it is stored.
Disadvantages (or ) Reason for Failure
Locating and retrieving a record is very difficult Process,because of its sequentialaccess method.Altering the file structure Such as updating a record is also heavy work .To do this job the entire file has to be read and rewritten
2. Hierarchical Database Systems [ HDS ]
In the Hierarchical database systems Data storage is in the format of a Parent - Child relationship . The orgin of a data tree is the root Data located at different levels along a particular branch from the root is called the NODE . The last node in the series is called LEAF . This method supports One - to - many relationship .
Disadvantages (or ) Reason for Failure
It is not possible to enter a new level in to the system . This model does not support Many - to- Many relationship .
3. Network Database Systems [ NDS ]
The main idea behind the NDS model is to bring about Many - to - Many relationship . The relationship between the different data items is called sets .This system also uses a pointer to locate a particular record.
Disadvantages (or ) Reason for Failure
The use of pointers leads to difficulty in the structure . As a results of the increased complicate mapping [ seraching ]of related data becomes very difficult
4. Relational Database Systems
Dr.E.F.Codd first introduced the Relational Database Model in 1970.
The Relational model allows data to be represented in a simple row - column .Each Datafield is considered as a column.Each Record is considered as a row of a column
Disadvantages (or ) Reason for Failure
The major disadvantage of the Relational model is that a clear cut interface cannot be determined . But Resuability of a structure is not possible.
5. ObjectRelational Database Systems
Object Relational Model support both object oriented and relational concepts.It eleminates certain difficulty in relational model .In this model it is possible to provide well defined interfaces[area] for the application.Structure once created can be re-used this is the fundamental property of the OOPs concepts .
