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Note for Database Engineering - DE By Sibo prasad Patro

  • Database Engineering - DE
  • Note
  • Biju Patnaik University of Technology BPUT - BPUT
  • Computer Science Engineering
  • 9 Topics
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Sibo Prasad Patro
Sibo Prasad Patro
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Introduction: In computerized information system data is the basic resource of the organization. So, proper organization and management for data is required fro organization to run smoothly. Database management system deals the knowledge of how data stored and managed on a computerized information system. In any organization, it requires accurate and reliable data for better decision making, ensuring privacy of data and controlling data efficiently. The examples include deposit and/or withdrawal from a bank,hotel,airline or railway reservation, purchase items from supermarkets in all cases, a database is accessed. What is data: Data is the known facts or figures that have implicit meaning. It can also be defined as it is the representation of facts ,concepts or instruction in a formal manner, which is suitable for understanding and processing. Data can be represented in alphabets(A-Z, a-z),in digits(0-9) and using special characters(+,-.#,$, etc) e.g: 25, ―ajit‖ etc. Information: Information is the processed data on which decisions and actions are based. Information can be defined as the organized and classified data to provide meaningful values. Eg: ―The age of Ravi is 25‖ File: File is a collection of related data stored in secondary memory. File Oriented approach: The traditional file oriented approach to information processing has for each application a separate master file and its own set of personal file. In file oriented approach the program dependent on the files and files become dependent on the files and files become dependents upon the programs Disadvantages of file oriented approach: 1) Data redundancy and inconsistency: The same information may be written in several files. This redundancy leads to higher storage and access cost. It may lead data inconsistency that is the various copies of the same data may longer agree for example a changed customer address may be reflected in single file but not else where in the system. 2) Difficulty in accessing data : The conventional file processing system do not allow data to retrieved in a convenient and efficient manner according to user choice. 3) Data isolation : Because data are scattered in various file and files may be in different formats with new application programs to retrieve the appropriate data is difficult. 4) Integrity Problems: Developers enforce data validation in the system by adding appropriate code in the various application program. How ever when new constraints are added, it is difficult to change the programs to enforce them. 2

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5) Atomicity: It is difficult to ensure atomicity in a file processing system when transaction failure occurs due to power failure, networking problems etc. (atomicity: either all operations of the transaction are reflected properly in the database or non are) 6) Concurrent access: In the file processing system it is not possible to access a same file for transaction at same time 7) Security problems: There is no security provided in file processing system to secure the data from unauthorized user access. Database: A database is organized collection of related data of an organization stored in formatted way which is shared by multiple users. The main feature of data in a database are: 1. It must be well organized 2. it is related 3. It is accessible in a logical order without any difficulty 4. It is stored only once for example: consider the roll no, name, address of a student stored in a student file. It is collection of related data with an implicit meaning. Data in the database may be persistent, integrated and shared. Persistent: If data is removed from database due to some explicit request from user to remove. Integrated: A database can be a collection of data from different files and when any redundancy among those files are removed from database is said to be integrated data. Sharing Data: The data stored in the database can be shared by multiple users simultaneously with out affecting the correctness of data. Why Database: In order to overcome the limitation of a file system, a new approach was required. Hence a database approach emerged. A database is a persistent collection of logically related data. The initial attempts were to provide a centralized collection of data. A database has a self describing nature. It contains not only the data sharing and integration of data of an organization in a single database. A small database can be handled manually but for a large database and having multiple users it is difficult to maintain it, In that case a computerized database is useful. The advantages of database system over traditional, paper based methods of record keeping are:  compactness: No need for large amount of paper files  speed: The machine can retrieve and modify the data more faster way then human being  Less drudgery: Much of the maintenance of files by hand is eliminated

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 Accuracy: Accurate,up-to-date information is fetched as per requirement of the user at any time. Database Management System (DBMS): A database management system consists of collection of related data and refers to a set of programs for defining, creation, maintenance and manipulation of a database. Function of DBMS: 1. Defining database schema: it must give facility for defining the database structure also specifies access rights to authorized users. 2. Manipulation of the database: The dbms must have functions like insertion of record into database updation of data, deletion of data, retrieval of data 3. Sharing of database: The DBMS must share data items for multiple users by maintaining consistency of data. 4. Protection of database: It must protect the database against unauthorized users. 5. Database recovery: If for any reason the system fails DBMS must facilitate data base recovery. Advantages of dbms: Reduction of redundancies: Centralized control of data by the DBA avoids unnecessary duplication of data and effectively reduces the total amount of data storage required avoiding duplication in the elimination of the inconsistencies that tend to be present in redundant data files. Sharing of data: A database allows the sharing of data under its control by any number of application programs or users. Data Integrity: Data integrity means that the data contained in the database is both accurate and consistent. Therefore data values being entered for storage could be checked to ensure that they fall with in a specified range and are of the correct format. Data Security: The DBA who has the ultimate responsibility for the data in the dbms can ensure that proper access procedures are followed including proper authentication schemas for access to the DBS and additional check before permitting access to sensitive data. Conflict resolution: DBA resolve the conflict on requirements of various user and applications. The DBA chooses the 4

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best file structure and access method to get optional performance for the application. Data Independence: Data independence is usually considered from two points of views; physically data independence and logical data independence. Physical data Independence allows changes in the physical storage devices or organization of the files to be made without requiring changes in the conceptual view or any of the external views and hence in the application programs using the data base. Logical data independence indicates that the conceptual schema can be changed without affecting the existing external schema or any application program. Disadvantage of DBMS: 1. DBMS software and hardware (networking installation) cost is high 2. The processing overhead by the dbms for implementation of security, integrity and sharing of the data. 3. centralized database control 4. Setup of the database system requires more knowledge, money, skills, and time. 5. The complexity of the database may result in poor performance. Database Basics: Data item: The data item is also called as field in data processing and is the smallest unit of data that has meaning to its users. Eg: ―e101‖,‖sumit‖ Entities and attributes: An entity is a thing or object in the real world that is distinguishable from all other objects Eg: Bank,employee,student Attributes are properties are properties of an entity. Eg: Empcode,ename,rolno,name Logical data and physical data : Logical data are the data for the table created by user in primary memory. Physical data refers to the data stored in the secondary memory. Schema and sub-schema : A schema is a logical data base description and is drawn as a chart of the types of data that are used . It gives the names of the entities and attributes and specify the relationships between them. A database schema includes such information as :

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