1. Database Models
The initial development of data storage started with the file system and these files have actually no relation or information of the application using these files. These files are accessed through the application containing the information or name of the files so these files cannot be considered as database but used to store information about the database. The application software is not aware of the structure of the file but as compared to it database management system consists of metadata and it is the responsibility of metadata to translate the files in physical layer as well as creation of logical layer. Conceptually metadata is that data which is stored in the catalog of database that how data is stored in database and how relationship would be developed among data. The example of flat file system is just like an application dealing with customer records through cutomer_data.txt.
1.1 Hierarchical Database Management System
In hierarchical modeling technique the database is bit revolutionized and organized and the scheme is just like the record file indicating the address of certain data or pointing towards the place of actual record. The following example shows that two pointers are clearly pointing towards the web page and street address but for the pointer address or URL could be taken from the record which one step above the actual information or data.
Figure 7. Hierarchical Model
The relationship in this case is parent child with one parent and many children.
1.2 Network Database Management System
Network database model is somewhat similar to the hierarchical data model but this model is first time developed by CODASYL network although initial network database was Honeywell IDS but it was not standardize at that time as network model. The network model developed by CODASY used same method of parent child relationship like hierarchical model. In this model a member record could have only one owner record for each type of set but record type can be member of more than one set.
Figure 8. Network Model
1.3 Relational Database Management System
Relational data model is not a new data modeling technology in the current century as its roots are linked with previous century as it was developed in 1969 by E.F Codd. Relational database model is widely used data modeling technique for the small and medium data storage systems all around the world.
The models are based on the logic and mathematics and management of data could be done with help of table sets not any type of individual data levels. A table consists of particular structure which is known as schema. In every table of there is one primary key for the identification of tuple. Values should be present in all of the columns of primary key and it is not allowed that columns having Null values. In relation database it important to understand the concept of referential integrity which is exact matching of foreign key in any other table with primary key. The data...