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Note for Database Management System - DBMS By Amity Kumar

  • Database Management System - DBMS
  • Note
  • Amity University - AMITY
  • Computer Science Engineering
  • 18 Topics
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1.1 • Characteristics of DBMS To incorporate the requirements of the organization, system should be designed for easy maintenance. • Information systems should allow interactive access to data to obtain new information without writing fresh programs. • System should be designed to co-relate different data to meet new requirements. • An independent central repository, which gives information and meaning of available data is required. • Integrated database will help in understanding the inter-relationships between data stored in different applications. • The stored data should be made available for access by different users simultaneously. • Automatic recovery feature has to be provided to overcome the problems with processing system failure. DBMS Utilities • A data loading utility: Which allows easy loading of data from the external format without writing programs. • A backup utility: Which allows to make copies of the database periodically to help in cases of crashes and disasters. • Recovery utility: Which allows to reconstruct the correct state of database from the backup and history of transactions. • Monitoring tools: Which monitors the performance so that internal schema can be changed and database access can be optimized. Page 4

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• File organization: Which allows restructuring the data from one type to another? 1.2 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. DBMS = Database Management System RDBMS = Relational Database Management System Page 5

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A database management system is, well, a system used to manage databases. A relational database management system is a database management system used to manage relational databases. A relational database is one where tables of data can have relationships based on primary and foreign keys. 1.3 Advantages of DBMS. Due to its centralized nature, the database system can overcome the disadvantages of the file system-based system 1. Data independency: Application program should not be exposed to details of data representation and storage DBMS provides the abstract view that hides these details. 2. Efficient data access.: DBMS utilizes a variety of sophisticated techniques to store and retrieve data efficiently. 3. Data integrity and security: Data is accessed through DBMS, it can enforce integrity constraints. E.g.: Inserting salary information for an employee. 4. Data Administration: When users share data, centralizing the data is an important task, Experience professionals can minimize data redundancy and perform fine tuning which reduces retrieval time. 5. Concurrent access and Crash recovery: DBMS schedules concurrent access to the data. DBMS protects user from the effects of system failure. 6. Reduced application development time. DBMS supports important functions that are common to many applications. Page 6

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1.4 Functions of DBMS • Data Definition: The DBMS provides functions to define the structure of the data in the application. These include defining and modifying the record structure, the type and size of fields and the various constraints to be satisfied by the data in each field. • Data Manipulation: Once the data structure is defined, data needs to be inserted, modified or deleted. These functions which perform these operations are part of DBMS. These functions can handle plashud and unplashud data manipulation needs. Plashud queries are those which form part of the application. Unplashud queries are ad-hoc queries which performed on a need basis. • Data Security & Integrity: The DBMS contains modules which handle the security and integrity of data in the application. • Data Recovery and Concurrency: Recovery of the data after system failure and concurrent access of records by multiple users is also handled by DBMS. • Data Dictionary Maintenance: Maintaining the data dictionary which contains the data definition of the application is also one of the functions of DBMS. • Performance: Optimizing the performance of the queries is one of the important functions of DBMS. 1.5 Role of Database Administrator. Typically there are three types of users for a DBMS: 1. The END User who uses the application. Ultimately he is the one who actually puts the data into the system into use in business. This user need not know anything about the organization of data in the physical level. 2. The Application Programmer who develops the application programs. He/She has more knowledge about the data and its structure. He/she can manipulate the data using his/her programs. He/she also need not have access and knowledge of the complete data in the system. 3. The Data base Administrator (DBA) who is like the super-user of the system. Page 7

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