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Note for Database Management System - DBMS By Krishna Mohan

  • Database Management System - DBMS
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File Based System 1. A file based system is a collection of application programs that perform services for the users wishing to access information. 2. Each program within a file based system defines and manages its own data. Because of this, there are limits as to how that data can be used or transported. 3. File based systems were developed as better alternatives to paper based filing systems. By having files stored on computers, the data could be accessed more efficiently. It was common practice for larger companies to have each of its departments looking after its own data. 4. A file-based system is a collection of data stored in an orderly manner in a file. It is a file packed with data, with no metadata and thus no organizing structure. 5. File bases systems store all data from the application as physical text files on the hard drive. This can be simpler in the short term, but presents problem as the site scales. 6. Any structure change to the file would need changes to the file as well as to the application programs accessing those files to process data. That means more change is needed making it rigid. Draw Backs of File Based System Although a computer file-based processing system has many advantages over manual record keeping system, but it has some limitations. The basic disadvantages (or limitations) of computer file-based processing system are described below. • Data Redundancy Redundancy means having multiple copies of the same data. In computer file-based processing system, each application program has its own data files. The same data may be duplicated in more than one file. The duplication of data may create many problems such as: 1. To update a specific data/record, the same data must be updated in all files, otherwise different file may have different information about a specific item. 2. A valuable storage space is wasted. • Data Inconsistency Data inconsistency means that different files may contain different information of a particular object or person. Actually redundancy leads to inconsistency. When the same data is stored in multiple locations, the inconsistency may occur. • Data Isolation In computer file-based system, data is isolated in separate files. It is difficult to update and to access particular information from data files.

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• Data Atomicity Data atomicity means data or record is either entered as a whole or it is not entered at all. • Data Dependence In computer file-based processing systems, the data stored in file depends upon the application program through which the file was created. It means that the structure of data files is coupled with application program. The physical structure of data files and records are defined in the application program code. It is difficult to change the structure of data files or records. If you want to change the structure of data file (or format of file), then you have to modify the application program. • Program Maintenance In computer file-based processing system, the structure of data file is coupled with the individual application programs. Therefore, any modification to a data file such as size of a data field, its type etc. requires the modification of the application program also. This process of modifying the program is referred to as program maintenance. • Data Sharing In computer file-based processing systems, each application program uses its own private data files. The computer file-based processing systems do not provide the facility to share data of a data file among multiple users on the network. • Data Security The computer file-based processing system does not provide the proper security system against illegal access of data. Anyone can easily change or delete valuable data stored in the data file. It is the most complicated problem of file-processing system. • Incompatible File Format In computer file-based processing systems, the structure of data file is coupled with the application program and the structure of data file is dependent on the programming languages in which the application program was developed Data and Information Data is the raw material that can be processed by any computing machine. Data can be represented in the form of: ▪ Numbers and words which can be stored in computer's language ▪ Images, sounds, multimedia and animated data as shown

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Information is data that has been processed in such a way as to be meaningful to the users who receives it. It is anything that is communicated. Information is needed to: • To gain knowledge about the surroundings, and whatever is happening in the society and universe. • To keep the system up to date. • To know about the rules and regulations and bye laws of society, local government, provincial and central government, associations, clients etc. as ignorance is no bliss. • Based on above three, to arrive at a particular decision for planning current and prospective actions in process of forming, running and protecting a process or system DATABASE 1. Database is a systematic collection of related data, typically describing the activities of one or more related organizations. 2. Databases support large amount of storage and provide ways to keep data up to date. Databases make data management easy 3. In addition to being a collection of related data, a database must have the following properties: • • • It represents some aspect of the real (or an imagined) world, called the miniworld or universe of discourse. Changes to the miniworld are reflected in the database. Imagine, for example, a UNIVERSITY miniworld concerned with students, courses, course sections, grades, and course prerequisites. It is a logically coherent collection of data, to which some meaning can be attached. (Logical coherency requires, in part, that the database not be self-contradictory.) It has a purpose: there is an intended group of users and some preconceived applications that the users are interested in employing. DATABASE MANAGEMENT SYSTEM A database management system (DBMS) is a collection of programs enabling users to create and maintain a database. DBMS is a general purpose software system facilitating each of the following: • • • • • • Defining: specifying data types (and other constraints to which the data must conform) and data organization Construction: the process of storing the data on some medium (e.g., magnetic disk) that is controlled by the DBMS Manipulation: querying, updating, report generation Sharing: allowing multiple users and programs to access the database "simultaneously" System Protection: preventing database from becoming corrupted when hardware or software failures occur Security: preventing unauthorized or malicious access to database.

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Difference between File system & DBMS File System 1. File system is a collection of data. Any management with the file system, user has to write the procedures 2. File system gives the details of the data representation and Storage of data. 3. In File system storing and retrieving of data cannot be done efficiently. 4. Concurrent access to the data in the file system has many problems like a. Reading the file while other deleting some information, updating some information 5. File system doesn’t provide crash recovery mechanism. Eg. While we are entering some data into the file if System crashes then content of the file is lost. 6. Protecting a file under file system is very difficult. DBMS 1. DBMS is a collection of data and user is not required to write the procedures for managing the database. 2. DBMS provides an abstract view of data that hides the details. 3. DBMS is efficient to use since there are wide varieties of sophisticated techniques to store and retrieve the data. 4. DBMS takes care of Concurrent access using some form of locking. 5. DBMS has crash recovery mechanism, DBMS protects user from the effects of system failures. 6. DBMS has a good protection mechanism.

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