APPENDIX A: Case Studies

Case Studies are designed to capture the reader’s interest. There are usually applications familiar to most readers. The cases could act as projects and could be carried out in parallel with studying the book.

The cases we will discuss here are

• The ATM
• The Library
• The Patient Monitoring System

The ATM

The ATM has a screen, a card reader, a small printer, a cash dispenser and a keyboard. The keyboard has numeric buttons, an enter key and a clear key. There are buttons on the sides of the screen to allow selection of any options displayed on the screen. The ATM is connected to the bank via a telephone line.

The ATM provides facilities to

• Dispense cash
• Display the current balance

The user must offer their card to the reader. The display then asks the user to enter their pin via the keyboard. If this is successful, the display offers a set of options to the user.

The Library

This application is a typical information system. Software is required to maintain information about books in the library, which is typically used by the library staff. The software must run on standard networked PC’s.

For each book, the following information is stored in the computer:

• Title
• Author
• ISBN
• Year
• Date of issue
• Borrower identification

The computer should be able to provide facilities to:

• Issue a book to a borrower
• Receive a book returned by a borrower
• Create information about a newly acquired book
• Display a list of books issued to a particular borrower

The facilities should be accessible by a GUI (Graphical User Interface). The computer should respond within one second to any request.

The system should provide a search facility to find out whether a book is available. When a book becomes overdue, the system should display appropriate information. Only the library staff should provide secured access to the system.

The software should be delivered by a particular date and its cost should not be more than USD$100,000. It must be fully documented and easy to maintain.

Patient Monitoring System

This is an example of safety-critical system.

A computer system maintains the vital signs of a patient in a hospital. Sensors attached to a patient continually send information to the computer:

• Heart rate
• Temperature
• Blood pressure

The computer displays the information on a screen. It also logs the information in a file so that it can be retrieved and displayed. If any of the vital signs exceeds the safe limits, the computer screen flashes a warning and an alarm sounds. The limits have default values but can be changed by the operator. If any sensor fails, the screen flashes a warning and the alarm sounds.