DBMS And RDBMS
What Is DBMS?
Data is one of the most important assets of a company. It is very important to make sure data is stored and maintained accurately and quickly. DBMS (Database Management System) is a system that is used to store and manage data. A DBMS is a set of programs that is used to store and manipulation data. Manipulation of data include the following:
1. Adding new data, for example adding details of new student.
2. Deleting unwanted data, for example deleting the details of students who have completed course.
3. Changing existing data, for example modifying the fee paid by the student.
A DBMS provides various functions like data security, data integrity, data sharing, data concurrence, data independence, data recovery etc. However, all database management systems that are now available in the market like Sybase, Oracle, and MS-Access do not provide the same set of functions, though all are meant for data management.
Database managements systems like Oracle, DB2 are more powerful and meant for bigger companies. Whereas, database management systems like MS-Access are meant for small companies. So one has to choose the DBMS depending upon the requirement.
Data model is a way of storing and retrieving the data. There are three different data models.
Data models differ in the way they allow users to view and manipulate relationships between entities. Each has its own way of storing the data. The following are the three different data models:
In this model, data is stored in the form of a tree. The data is represented by parent-child relationship. Each tree contains a single root record and one or more subordinate records. For example, each batch is root and students of the batch will be subordinates. This model supports only one-to-many relationship between entities. This was used in IBM’s Information management system, IMS.
Data is stored along with pointers, which specify the relationship between entities. This was used in Honeywell's Integrated Data Store, IDS. This model is complex. It is difficult to understand both the way data is stored and the way data is manipulated. It is capable of supporting many-to-many relationship between entities, which hierarchical model doesn’t.
This stores data in the form of a table. Table is a collection of rows and columns.
Relational Database Management System (RDBMS)
A DBMS that is based on relational model is called as RDBMS. Relation model is most successful mode of all three models. Designed by E.F. Codd, relational model is based on the theory of sets and relations of mathematics. Relational model represents data in the form a table. A table is a two dimensional array containing rows and columns. Each row contains data related to an entity such as a student. Each column contains the data related to a single attribute of the entity such as student name. One of the reasons behind the success of relational model is its simplicity. It is easy to understand the data and easy to manipulate. Another important advantage with relational model, compared with remaining two models is, it doesn’t bind data with relationship between data item. Instead it allows you to have dynamic relationship between entities using the values of the columns. Almost all Database systems that are sold in the market, now- a-days, have either complete or partial implementation of relational model.
Figure 1 shows how data is represented in relational model and what are the terms used to refer to various components of a table. The following are the terms used in relational model.