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Note for Database Management System - DBMS By Binod PEC

  • Database Management System - DBMS
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Chapter 1 Introduction to Database Management System 1.1 Data : In simple words data can be facts related to any object in consideration. For example our name, age, height, weight, etc are some data related to us. A picture , image , file , pdf etc can also be considered data. Data is rarely useful in its raw form. For example, in a banking application, data is the whole collection of bank account numbers; bank customers’ names, addresses, and ages; bank transactions and so on. However, when data is arranged relationally, it then becomes information, which is much more useful to users. Data are logically organized into: 1. Bits A bit is the smallest unit of data representation (value of a bit may be a 0 or 1) 2. Fields A data field represents an attribute (a characteristic or quality) of some entity (object, person, place, or event) 3. Records A record consists of fields, with each field describing an attribute of the entity. 4. Files A group of related records 5. Databases Collection of logically related records or files. 1.2 Database : A database is a collection of data that is saved and organized to allow easy retrieval when needed. It is the collection of schemas, tables, queries, reports, views, and other objects. In order to maintain and access the database we need a DBMS (database management system). Databases consists of tables that include groups of related data fields that are known as records. Databases are not limited to only computers; in fact, a phone book is an example of a database. Some of the examples of database applications are telephone directory system, Computerized Library, Inventory System etc. Early databases were relatively "flat" which means they were limited to simple rows and columns, like a spreadsheet. 1.2.1 Types of Database: 1. Relational database :A tabular database in which data is defined so that it can be reorganized and accessed in a number of different ways. It stores data in tables with relationships to other tables. 2. Distributed database :A distributed database is one that can be dispersed or replicated among different point in a network.

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3. Object oriented programming database :In this database, the data is defined in object classes and sub classes. 1.3 Database Management System: A database-management system (DBMS) is a computer-software application that interacts with end-users, other applications, and the database itself to capture and analyze data. A database management system (DBMS) is system software for creating and managing databases. The DBMS provides users and programmers with a systematic way to create, retrieve, update and manage data. Examples of DBMS are MS-Sql Server, MySQL, MS-Access, dBase, Oracle etc. 1.3.1 Application of DBMS ✔ Banking: For customer and their account information. ✔ Airlines: For reservation and schedules information. ✔ Telecommunications: Maintaining the bills, calls and other useful information. ✔ Government: For Taxes, Budgets, and Census. ✔ Sales: For inventory, Customers information, purchase and sales information. ✔ Universities: For maintaining student records, course registration and grades.

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1.3.2 Advantages of DBMS 1. Minimal Data Redundancy: Data Redundancy means that the same data field appears in different files and format i.e. Duplication of data. So the waste of storage is reduced. 2. Sharing of Data: The data sharing feature of DBMS allows the data to be shared among the existing applications and newly developed application without having to create any additional stored data. 3. Increased Security: The DBMS creates a security system that enforces user security and data privacy within the database. 4. Better Service to Users: The DBMS allow users who don’t know any programming language to interact with the data more easily. 5. Features of Backup and Recovery: Backup is a task of creating a copy of original data so that the data can be recovered in case of data loss. 1.3.3 Disadvantages of DBMS 1. Cost of Hardware and Software: A processor with high speed of data processing and memory of large size is required to run the DBMS software . DBMS software is also very costly. 2. Database Failures: In most of the organizations, all data is Centralized. If database is corrupted due to power failure or it is corrupted on the storage media, then our valuable data may be lost or whole system stops. 3. Complexity of Backup and Recovery: Since data is centralized, adequate backup of the data is necessary so that in case of failure data can be recovered. So backup problem is also the drawback. 4. Appointing Technical Staff: The trained technical persons such as database administrator and application programmers etc are required to handle the DBMS. We have to pay high salaries to these persons. Therefore, the system cost increases. 5. Larger File Size: The DBMS itself is large program so additional memory is required. 1.3.4 Components of DBMS A DBMS is an intermediate link between the physical database, computer and operating system and on the other hand users. There are 5 components in database system environment and they are 1. Hardware:

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2. 3. 4. 5. The hardware is the actual computer system for keeping and accessing the database. The DBMS hardware consists of secondary storage device like hard disk on which the database physically resides, input output devices etc. Software: The software is the actual DBMS. A DBMS is software that provides interface between the user and physical database for accessing the data. All requests from users for access to the database are handled by DMBS. Data: Data stored in database includes numerical data, non numerical data such as characters, logical values and complex data such as images. In addition to these operational data, the database contains meta-data, the data of data. Users: There are a number of users who can access or retrieve data on demand using the application and interfaces provided by DBMS. Procedures: Procedure refers to the rules that govern the design and use of the database. There must be a documented rule for the database users on how to use or run the system. Some of them may be a. Logon to DBMS b. Use Particular DBMS facility or application program c. Make backup copies of Database d. Handle hardware and software failure 1.4 File Environment The traditional filing system is a method of storing and arranging computer files and the information in the file. For this method, a file name is assigned to a file in order to secure storage location in the computer memory or data storage devices such as hard disks or CD-ROMs are used to maintain the physical location of the files. By this file name a file can be further accessed. Whether the file system has an underlying storage device or not, file systems typically have directories which associate file names with files, usually by connecting the file name to an index in a file allocation table. A new concept for file management is the concept of a database-based file system 1.4.1 Advantages of traditional file based system ✗ No need of external storage ✗ No need of a highly technical person to handle the database.

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