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Note for Database Management System - DBMS by harika emany

  • Database Management System - DBMS
  • Note
  • Computer Science Engineering
  • B.Tech
  • 11 Topics
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____________________________________D Daattaabbaassee M Maannaaggeem meenntt SSyysstteem mss - location called repository or catalog. This repository is used by DBMS software and also by Database users who need information about the Database structure. In traditional file processing, a data definition is a part of the application programs themselves. So these programs are constrained to work with only one specific Database, whose structure is declared in the application programs. 1. The file processing software can access only specific Databases, whereas DBMS software can access number of Databases by extracting Database definitions from the repository. 2. In file processing software, when a request can made by a user, the exact location of that record was known by the application program and then locate that record, whereas in DBMS the DBMS software refers the repository to determine the structure of the Database and then find the record location. b) Insulation between programs and data and data abstraction In traditional file processing system, the structure of data file is included in the programs, so any changes to the structure of a data file may require changing all programming that access that file. But in DBMS, the access program don’t require changes the structure of the file, because the structure of Database or data file is stored in repository which is centralized location to all access programs of the programs. This property is known as program data independence. In object oriented Databases, users can define operations on data as part of the Database definitions. An operation can be in two parts. The interface and implementation. The interface includes the operation name and the data types of its arguments. The implementation (function/method) is specified separately and can be changed without effecting the interface. The user application programs can operate on data by invoking the operations with their arguments rather than how the operations are implemented. This is called program-operation independence. This characteristic that allows both program data independence and program operation independence is called as data abstraction. c) Support multiple views of data A view is a subset of Database or it may contain virtual data that may derive from a base table or Database. A multi user DBMS whose users may have several applications must provide facilitate for defining multiple views on one Database. d) Sharing of data and multi user transaction processing 3 ********TVSN KLU ECM*********

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____________________________________D Daattaabbaassee M Maannaaggeem meenntt SSyysstteem mss A Client/Server or multiuser DBMS must allow multiple users to access the Database at the same time. For this the DBMS must include concurrency control software to ensure that several users trying to update the same data. These updations are maintained by the concurrent control software. Also these types of applications are referred as OLAP applications. 6. Explain the advantages of using DBMS? For good DBMS software, there are several advantages. They are: a) Controlling redundancy. b) Restricting unauthorized access. c) Providing persistent storage for program objects and data structures. d) Permitting interfering and actions using rules. e) Providing multiple user interfaces. f) Representing complex relationships and data. g) Enforcing integrity constraints. h) Providing backup and recovery. a. Controlling redundancy Redundancy means, storing of same data multiple times in multiple files. This leads several problems. 1. If any data item needs to update, it need to update multiple times. 2. Storage space was waster when a system have redundancy. This may creates problem when we use large Databases. 3. Due to redundancy the data consistency was in very high rate. In DBMS, due to we have repository/catalog, the data can be stored at a centralized location, utmost redundancy was eliminated/controlled. When the redundancy was controlled, it will be improved the Database engine’s performance. b. Restricting unauthorized access When we have multiple user environments, typically the Client/Server environment, the users share a Database. In those, some users are fully authorized and some users are partial authorized. Some users may permitted on only retrieving or selection operation, some users may permitted to update and others may permitted both operations. To restrict this type of accessing, the DBMS has given an account name and passwords for each user group. Also the DBMS should provide a security and authorization subsystem. Some users called DBA may only have fully privileged user groups. c. Providing persistent storage for program objects and data structure Databases can be used to provide persistent storage for programs and the data Structures (data members/data objects). For ordinary Databases the DBMS used to store 4 ********TVSN KLU ECM*********

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____________________________________D Daattaabbaassee M Maannaaggeem meenntt SSyysstteem mss ordinary storage, but in object oriented databases, persistent/continuous storage technology is used. d. Permitting interfering and actions using rules Some Database systems, such as Oracle, Sybase, etc., provide capabilities for defining deduction rules for interfacing new information from the stored Database facts. In any situation, if there may exists any critical situation for entering and extracting data, these packages are used procedural languages such as PL/SQL. e. Providing multiple user interface The DBMS provide back end facility to all types of GUI (Graphical User Interface) application such as Visual Basic, VC++, Java, Power Builder, etc. these application are used ODBC or JDBS connections to interact with DBMS. f. Representing complex relationships and data A DBMS package must have capability to represent a numerous verities of relationships from one Database to another. Besides of relationships, also provide proper operations such as selection/retrieving, updating and deleting on data. g. Enforcing integrity constraints Restricting the incoming data using some conditions is known as integrity constraints. These constraints are also used to hold proper data in Database. The DBMS provide a verity of integrity constraints to hold proper data. The Database designers take the responsibility to identify the integrity constraints during the Database design. h. Providing backup and recovery Each DBMS should have contained backup and recovery subsystem. This subsystem is responsibility for recovering data from sudden hardware and software failures. The subsystem could also ensure that the program in resumed from the point at which the Database was interrupted. 7. What are the responsibilities of the DBA and Database designers? Database Administrator In Database environment the primary object is Database and DBMS. Administrating these resources is the responsibility of the DBA. The DBA is responsible for: 1. Authorizing access to the Database. 2. Coordinating and monitoring of Database and DBMS. 3. Acquiring software and hardware resources to the environment as it needed. 4. Maintain an account for problems such as security and poor system response time. 5 ********TVSN KLU ECM*********

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____________________________________D Daattaabbaassee M Maannaaggeem meenntt SSyysstteem mss 5. At the end of the day or end or the week or end of 15 days or end of the month the DBA should take the backup of Database. Database Designers The main responsibilities of Database designers are: 1. Identifying the data to be stored in the Database. 2. Choose appropriate structure represent and store the data. 3. Very important responsibility is, to communicate with all types of Database users in order to understand their requirements. 4. To conduct meets to discuss the design issues to meet the requirements of the end users. 5. Interact with programmers, analysts and the other users to get proper view of a Database. List out some additional advantages of DBMS: In addition to the advantages of DBMS we have some more implications. They are: a. Potential for enforcing Standards. b. Reduced application development time. c. Flexibility. d. Availability of up-to-date information. e. Economics of sales. a. Potential for enforcing Standards Since the database approach has being maintained a repository, it permits the DBA to define and enforce standards (some standards are predefined by the DBMS, and some standards are defined by the organization itself) among the databases. This facility will allows to communicate and cooperation among departments, projects and users (users may include database analysts, software engineers or database programmers). The administrator will enforce standards such as naming conventions, data quality standards, and procedures for accessing, updating and protecting data on databases. b. Reduced application development time Since the database approach has being maintained the centralized database, the development time will reduced compared to traditional file processing. Designing and implementation from scrap will take less time than traditional file processing. Also half completed will take very less time. c. Flexibility 6 ********TVSN KLU ECM*********

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