Lesson 01 Database Management System

Editor's Notes

• #2: The database is now such an integral part of our day-to-day life that often we are not aware that we are using one.
• #4: 1.) When you purchase goods from your local supermarket, it is likely that a database is accessed. The checkout assistant uses a bar code reader to scan each of your purchases. This reader is linked to a database application that uses the bar code to find out the price of the item from a product database. 2.) When you make inquiries about a vacation, your travel agent may access several databases containing vacation and flight details. When you book your vacation, the database system has to make all the necessary booking arrangements. In this case, the system has to ensure that two different agents do not book the same vacation or overbook the seats on the flight. For example, if there is only one seat left on the flight from New York to London and two agents try to reserve the last seat at the same time, the system has to recognize this situation, allow one booking to proceed, and inform the other agent that there are now no seats available. 3.) If you are at college, there will be a database system containing information about yourself, your major and minor fields, the courses you are enrolled in, details about your financial aid, the classes you have taken in previous years or are taking this year, and details of all your examination results.
• #5: For example, an organization might have physical files set up to hold all external and internal correspondence relating to a project, product, task, client, or employee. Typically, there are many such files, and for safety they are labeled and stored in one or more cabinets. For security, the cabinets may have locks or may be located in secure areas of the building. --The manual filing system works well as long as the number of items to be stored is small.
• #6: 1.) When data is isolated in separate files, it is more difficult to access data that should be available. For example, if we want to produce a list of all houses that match the requirements of clients, 2.) Duplication of data 3.) The program is exposed to changes 4.) For example, the structure of a file generated by a COBOL program may be different from the structure of a file generated by a C program. 5.) • There was no provision for security or integrity. • Recovery, in the event of a hardware or software failure, was limited or nonexistent. • Access to the files was restricted to one user at a time—there was no provision for shared access by staff in the same department.
• #7: To become more effective, a new approach was required. The database is a single, possibly large repository of data that can be used simultaneously by many departments and users. DATA ABSTRACTION: we can change the internal definition of an object without affecting the users of the object, provided that the external definition remains the same. Database approach separates the structure of the data from the application programs and stores it in the database.
• #8: Another expression in the definition of a database that we should explain is “logically related.” When we analyze the information needs of an organization, we attempt to identify entities, attributes, and relationships. Example: • Six entities: Branch Staff PropertyForRent, Client PrivateOwner Lease • Seven relationships: Has, Offers, Oversees, Views, Owns, LeasedBy, and Holds; • Six attributes, one for each entity: branchNo, staffNo, propertyNo, clientNo, ownerNo, and leaseNo. SIMPLE EXAMPLE: SCHOOL store data of Student, Teacher, Course, Rooms, Grades.