Database Management System

 Database Concepts

 Basic Concepts and Definitions the key to organizational success is effective decision making which requires timely, relevant and accurate information. Hence, information plays a critical role in today's competitive environment. Database Management Software (DBMS) simplifies the task of managing the data and extracting useful information out of it. In this chapter, we shall learn about the basic concepts of databases and learn how to use DBMS for some applications.

Basic Concepts and Definitions

The key to organizational success is effective decision making which requires timely, relevant and accurate information. Hence, information plays a critical role in today's competitive environment. Database Management Software (DBMS) simplifies the task of managing the data and extracting useful information out of it. In this chapter, we shall learn about the basic concepts of databases and learn how to use DBMS for some applications. Data is a collection of raw facts, which have not been processed to reveal useful information. Information is produced by processing data.

Data -> Processing -> Information

Databases are being used extensively in our day-to-day life. Be it business, engineering, medicine, education, library, to name a few. For example, consider the name, class; roll number, marks in every subject of every student in a school. To record this information about every student in a school, the school might have maintained a register, or stored it on a hard drive using a computer system and software such as a spreadsheet or DBMS package. Such collection of related data that has been recorded, organized and made available for searching is called a Database.

A database has the following properties:

1) A database is a representation of some aspect of the real world also called mini world. Whenever there are changes in this mini world, they are also reflected in the database.

2) It is designed, built and populated with data for specific purpose.

 3) It can be of any size and complexity.

 4) It can be maintained manually or it may be computerized.

Need for a Database  

In traditional file processing, data is stored in the form of files. A number of application programs are written by programmers to insert, delete, modify and retrieve data from these files. New application programs will be added to the system as the need arises. For example, consider the Sales and Payroll departments of a company. One user will maintain information about all the salespersons in the Sales department in some file say File1 and another user will maintain details about the payroll of the salesperson in a separate file say File2 in the Payroll Department.

1. Data Redundancy: Same information is stored in more than one file. This would result in wastage of space.

 2. Data Inconsistency: If a file is updated then all the files containing similar information must be updated else, it would result in inconsistency of data.

3. Lack of Data Integration: As data files are independent, accessing information out of multiple files becomes very difficult.

Database approach overcomes these problems and also adds a lot of advantages as discussed later. In database approach, a single repository of data is maintained which different users as per their needs access.

Database Management System (DBMS)

A database management system is a collection of programs that enables users to create, maintain and use a database. It enables creation of a repository of data that is defined once and then accessed by different users as per their requirements. Thus, there is a single repository of data, which is accessed by all the application programs as shown. 

The various operations that need to be performed on a database are as follows:

 1. Defining the Database: It involves specifying the data type of data that will be stored in the database and also any constraints on that data.

2. Populating the Database: It involves storing the data on some storage medium that is controlled by DBMS.

3. Manipulating the Database: It involves modifying the database, retrieving data or querying the database, generating reports from the database etc.

4. Sharing the Database: Allow multiple users to access the database at the same time.

5. Protecting the Database: It enables protection of the database from software/ hardware failures and unauthorized access.

6. Maintaining the Database: It is easy to adapt to the changing requirements. Some examples of DBMS are – MySQL, Oracle, DB2, IMS, and IDS etc.

Characteristics of Database Management Systems

The main characteristics of a DBMS are as follows:

 1. Self-describing Nature of a Database System: DBMS contains not only the database but also the description of the data that it stores. This description of data is called Meta[1]data. Meta-data is stored in a database catalogue or data dictionary. It contains the structure of the data and the constraints that are imposed on the data.

2. Insulation Between Programs and Data: Since the definition of data is stored separately in a DBMS, any change in the structure of data would be done in the catalogue and hence programs, which access this data, need not be modified. This property is called Program-Data Independence.

3. Sharing of Data: A multiuser environment allows multiple users to access the database simultaneously. Thus, a DBMS must include concurrency control software to allow simultaneous access of data in the database without any inconsistency problems.

Types of Users of DBMS

 1. End Users: Users who use the database for querying, modifying and generating reports as per their needs. They are not concerned about the working and designing of the database. They simply use the DBMS to get their task done.

 2. Database Administrator (DBA): As the name implies, the DBA administers the database and the DBMS. The DBA is responsible for authoring access, monitoring its use, providing technical support, acquiring software and hardware resources.

 3. Application Programmers: Application programmes write application programs to interact with the database. These programs are written in high-level languages and SQL to interact with the database.

4. System Analyst: System analyst determines the requirements of the end users and then develops specifications to meet these requirements. A system analyst plays a major role in the database design and all the technical, economic and feasibility aspects.

Advantages of using DBMS Approach

The need of DBMS itself explains the advantages of using a DBMS. Following are the advantages of using a DBMS:

1. Reduction in Redundancy: Data in a DBMS is more concise because of the central repository of data. All the data is stored at one place. There is no repetition of the same data. This also reduces the cost of storing data on hard disks or other memory devices.

2. Improved Consistency: The chances of data inconsistencies in a database are also reduced as there is a single copy of data that is accessed or updated by all the users.

3. Improved Availability: Same information is made available to different users. This helps sharing of information by various users of the database.

4. Improved Security: Though there is improvement in the availability of information to users, it may also be required to restrict the access to confidential information. By making use of passwords and controlling users' database access rights, the DBA can provide security to the database.

5. User Friendly: Using a DBMS, it becomes very easy to access, modify and delete data. It reduces the dependency of users on computer specialists to perform various data related operations in a DBMS because of its user-friendly interface.

Limitations of using DBMS Approach

The two main disadvantages of using a DBMS:

 1. High Cost: The cost of implementing a DBMS system is very high. It is also a very time[1]consuming process, which involves analyzing user requirements, designing the database specifications, writing application programs and then providing training.

 2. Security and Recovery Overheads: Unauthorized access to a database can lead to four Database Management Applications threat to the individual or organization depending on the data stored. In addition, the data must be regularly backed up to prevent its loss due to fire, earthquakes, etc. Hence the DBMS approach is usually not preferred when the database is small, well defined, less frequently changed and used by few users.