Note for Database Management System - DBMS By Mohit Kaushik

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Database Management Systems UNIT-1 Data: It is a collection of information. The facts that can be recorded and which have implicit meaning known as 'data'. Example: Customer ----- 1.cname. 2.cno. 3.ccity. Database: It is a collection of interrelated data. These can be stored in the form of tables. A database can be of any size and varying complexity. A database may be generated and manipulated manually or it may be computerized. Example: Customer database consists the fields as cname, cno, and ccity Cname Cno Ccity Database System: It is computerized system, whose overall purpose is to maintain the information and to make that the information is available on demand. Advantages: 1.Redundency can be reduced. 2.Inconsistency can be avoided. 3.Data can be shared. A.I.J.H.M COLLEGE ROHTAK

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2 4.Standards can be enforced. 5.Security restrictions can be applied. 6.Integrity can be maintained. 7.Data gathering can be possible. 8.Requirements can be balanced. Database Management System (DBMS): It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications. Disadvantages in File Processing Data redundancy and inconsistency. Difficult in accessing data. Data isolation. Data integrity. Concurrent access is not possible. Security Problems. . Advantages of DBMS: 1.Data Independence. 2.Efficient Data Access. 3.Data Integrity and security. 4.Data administration. 5.Concurrent access and Crash recovery. 6.Reduced Application Development Time. Applications Database Applications: Banking: all transactions Airlines: reservations, schedules Universities: registration, grades Sales: customers, products, purchases Online retailers: order tracking, customized recommendations Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions People who deal with databases Many persons are involved in the design, use and maintenance of any database. These persons can be classified into 2 types as below. Actors on the scene: The people, whose jobs involve the day-to-day use of a database are called as 'Actors on the scene', listed as below. 1.Database Administrators (DBA): The DBA is responsible for authorizing access to the database, for Coordinating and monitoring its use and for acquiring software and hardware resources as needed. These are the people, who maintain and design the database daily. DBA is responsible for the following issues. A.I.J.H.M COLLEGE ROHTAK

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3 a. Design of the conceptual and physical schemas: The DBA is responsible for interacting with the users of the system to understand what data is to be stored in the DBMS and how it is likely to be used. The DBA creates the original schema by writing a set of definitions and is Permanently stored in the 'Data Dictionary'. b. Security and Authorization: The DBA is responsible for ensuring the unauthorized data access is not permitted. The granting of different types of authorization allows the DBA to regulate which parts of the database various users can access. c. Storage structure and Access method definition: The DBA creates appropriate storage structures and access methods by writing a set of definitions, which are translated by the DDL compiler. d. Data Availability and Recovery from Failures: The DBA must take steps to ensure that if the system fails, users can continue to access as much of the uncorrupted data as possible. The DBA also work to restore the data to consistent state. e. Database Tuning: The DBA is responsible for modifying the database to ensure adequate Performance as requirements change. f. Integrity Constraint Specification: The integrity constraints are kept in a special system structure that is consulted by the DBA whenever an update takes place in the system. 2.Database Designers: Database designers are responsible for identifying the data to be stored in the database and for choosing appropriate structures to represent and store this data. 3. End Users: People who wish to store and use data in a database. End users are the people whose jobs require access to the database for querying, updating and generating reports, listed as below. a. Casual End users: These people occasionally access the database, but they may need different information each time. b. Naive or Parametric End Users: Their job function revolves around constantly querying and updating the database using standard types of queries and updates. c. Sophisticated End Users: These include Engineers, Scientists, Business analyst and others familiarize to implement their applications to meet their complex requirements. d. Stand alone End users: These people maintain personal databases by using ready-made program packages that provide easy to use menu based interfaces. 4.System Analyst: These people determine the requirements of end users and develop specifications for transactions. 5.Application Programmers (Software Engineers): These people can test, debug, document and maintain the specified transactions. A.I.J.H.M COLLEGE ROHTAK

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4 b. Workers behind the scene: Database Designers and Implementers: These people who design and implement the DBMS modules and interfaces as a software package. 2.Tool Developers: Include persons who design and implement tools consisting the packages for design, performance monitoring, and prototyping and test data generation. 3.Operators and maintenance personnel: These re the system administration personnel who are responsible for the actual running and maintenance of the hardware and software environment for the database system. 3.LEVELS OF DATA ABSTRACTION This is also called as 'The Three-Schema Architecture’, which can be used to separate the user applications and the physical database. 1.Physical Level: This is a lowest level, which describes how the data is actually stores. Example: Customer account database can be described. 2.Logical Level: This is next higher level that describes what data and what relationships in the database. Example: Each record type customer = record cust_name: sting; cust_city: string; cust_street: string; end; 3.Conceptual (view) Level: This is a lowest level, which describes entire database. Example: All application programs. 4.DATA MODELS The entire structure of a database can be described using a data model. A data model is a collection of conceptual tools for describing Data models can be classified into following types. 1.Object Based Logical Models. 2.Record Based Logical Models. 3.Physical Models. Explanation is as below. 1.Object Based Logical Models: These models can be used in describing the data at the logical and view levels. These models are having flexible structuring capabilities classified into following types. a) The entity-relationship model. b) The object-oriented model. c) The semantic data model. d) The functional data model. 2.Record Based Logical Models: These models can also be used in describing the data at the logical and view levels. These models can be used for both to specify the overall logical structure of the database and a higher-level description. These models can be classified into, A.I.J.H.M COLLEGE ROHTAK