Introduction to Databases Lecture Notes PDF

Introduction to Databases Lecture Outline Introduction Traditional File-Based Systems Database Approach Roles in the Database Environment DBMS Advantages and Disadvantages of DBMSs Introduction Collection of logically related data is called database. A database may be of an...

Introduction to Databases Lecture Outline Introduction Traditional File-Based Systems Database Approach Roles in the Database Environment DBMS Advantages and Disadvantages of DBMSs Introduction Collection of logically related data is called database. A database may be of any size and complexity. Salesperson may contain a small database of customer contacts. A large corporation may build a large database. Introduction Other examples of database applications can be: Purchases from the supermarket. Purchasing using your credit card. Booking a holiday at the travel agent. Booking an airline ticket etc Introduction A software or tool that is used to manage and control the access to the database is called database management systems. A database application is simply a program that interacts with the database at some point in its execution. A database system is a collection of application programs that interact with the database along with the DBMS and database itself. Traditional File Processing System File-based system is a collection of application programs that perform services for the end-users such as the production of reports. Each program defines and manages its own data. Early attempt to computerize the manual filing system. Files in cabinet and locks for security. For searching we may have indexing system that helps locate what we want quickly. Works well While number of items to be stored is small. For only storage or retrieval functionality of large number of Traditional File Processing System The manual system becomes more inefficient while processing the information in the files. Typical real estate agent’s office holds two separate files: File for each property for sale or rent. File for each buyer and renter, and each member of staff. Traditional File Processing System Contract Department Sales Department Traditional File Processing System Consider the efforts that would be required to answer the following questions: File-Based Approach The file-based system was developed in response to the needs of industry for more efficient data access. Based on decentralized approach, where each department, with the assistance of Data Processing (DP) staff, stored and controlled its own data. File-Based Approach File-Based Approach Significant amount of duplication of data. Before to discuss the limitations, it is useful to understand the terminology used in file-based systems. A file is simply a collection of records, which contains logically related data. For example, the PropertyForRent file contains six fields, one for each property. Each record contains a logically connected set of one or more fields. Each field represents some characteristics of the real-world object that is being modeled. Limitations of File-Based Approach Separation and isolation of data Each program maintains its own set of data. Users of one program may be unaware of potentially useful data held by other programs. Duplication of data Decentralized approach taken by each department. Same data is held by different programs. Wasted space, money and time and perhaps more importantly data integrity; in other words data consistency. Limitations of File-Based Approach Data Dependence File structure is defined in the program code. Also known as a Program-Data dependence. Incompatible file formats Programs are written in different languages, and so cannot easily access each other’s files. Fixed Queries/Proliferation of application programs Programs are written to satisfy particular functions. Any new requirement needs a new program. The Database A shared collection of logically related data, and a description of this data, designed to meet the information needs of an organization – Database. Integrated with a minimum amount of duplication. Shared corporate resource. Also holds the description of the data. Description of data is known as the system catalog (or data dictionary or metadata – the ‘data about data’). Data abstraction. Database Approach All the above limitations of file-based approach can be listed as: The definition of the data is embedded in the application programs, rather than being stored separately and independently. There is no control over the access and manipulation of data outside that forced by the application programs. The above limitations were overcome with the new approach called database approach (database and DBMS). Database Management System A software system that enables users to define, create, maintain, and control access to the database. The DBMS is the software that interacts with the users’ application programs and the database.