Introduction
There are different types of Database Management System models used for organizing the data systematically in logical order. The following are the known data models:
- Flat File System
- Hierarchical Model
- Network Model
- Relation Model
- Object-oriented Model
Flat File System
Flat file is the most basic way to store data. The structure in flat file is very simple as data is stored in a single large table in plain text form. Each row holds only one record separated by delimiters like comma (,), semicolon (;), tab, etc. There is no relationship between the records. Word documents are considered to hold data in file system.
If we take an example of student records, file stores all the data of the student in a single row. If the student enrolls in a course, the details are stored in same row. Later, if the student enrolls in another course, then the same row will be added again with different course details. So there are chances of duplicate data. In case the student address is changed, there is a possibility that the address is updated in only one row while the other rows still hold the old address, which may cause redundant data.
Hierarchical Model
In hierarchical model, data is stored in tree form. There is a parent-child relationship between the records, i.e., one-to-many relationship. Hierarchy means that the data is arranged in different levels. The records are connected to each other through links. Each record can have one parent node called Root and multiple child nodes. The Information Management System (IMS) database, developed at IBM for Apollo Space in 1960s, is a hierarchical database.
Network Model
Charles Bachman invented network model. In Network model, a record can have multiple parent nodes and many child nodes i.e. it maintains many-to-many relationship. Entities and their relationships are presented more flexibly as compared to Hierarchical model. In network model, a data node can have multiple parents as compared to hierarchical model where the data node can have only one parent. So network model allows navigation of records through several paths. Few popular network databases are IDS (Integrated Data Store), RDM Server, IDMS (Integrated Database Management System), Univac DMS-1100.
Relational Model
Among all the models, the relational model is the most popular and widely used model designed by E.F. Codd. In this model, data is organized in 2 dimensional table in the form of rows and columns. The table is called a relation. A row is called an entity while a column is an attribute of the entity. RDBMS allows multiple tables linked together with relationships.
Object-oriented Model
Object Relational Database Management System (ORDBMS) resembles RDBMS with introduction of objects, classes and inheritance. ORDBMS is capable of handling very large and highly complex data. ORDBMS allows defining custom data types which are implemented as objects. Data encapsulation, abstraction and independence are the main objectives of this model.
