1. 1 Specification of IT Systems Mandatory Exercise Week 1 Group 3

2. 2 Traffic light Traffic light controller This system is a system that controls traffic lights on an intersection. The controller gets input about any cars waiting and where they are. Also input from waiting pedestrians and from a time device. Depending on the input, the controller changes the lights as needed.

3. 3 Traffic light - Subject domain Physical Entity: Light beacon Sensor Road Car Button Conceptual Entity: Green light Red light Yellow light

4. 4 Traffic light - Connection domain Sensor

5. 5 Traffic light - Cause and effect chain Event: A car approaches the intersections or a pedestrian. Events that may happen anyway: Pedestrian cross. Stimulus: Car approaches, pedestrian pushes the button, time interval has elapsed. Response: The light changes. Action: Car crosses the intersection, pedestrian crosses.

6. 6 Traffic light - Requirements Must reliable.

7. 7 Traffic light - Constraints The system can not physically constrain cars.

8. 8 Booking System (DGI) This is a system that handles sessions for members of the gym DGI. Different types of session include 1½ hour training in the gym, or the use of a badminton court for 1 hour. Booking a session and paying for a session is done online.

9. 9 Booking System (DGI) - Subject domain Physical Entity: Computer Customer Administrator Conceptual Entity: Session Lexical Entity: Webpage

10. 10 Booking System (DGI) - Cause and effect chain Event: Customer chooses an open timeslot Events that may happen anyway: Customer doesn’t find an open timeslot Stimulus: The system marks the timeslot as taken by the customer Response: System sends an order confirmation by text message to the customer. Action: Customer is happy

11. 11 Booking System (DGI) - Requirements The system must be reliable.

12. 12 Booking System (DGI) - Constraints The system cannot check for errors by administrators.

13. 13 Online travel agency The system is an online version of a travel agency that offers travels (flight, hotel, car rental, day tours,..) to customers. The customer can plan his dream vacation by searching for a suitable flight, hotel, day tour or car rental. Most of the products will be supplied from specialized online travel services and some will be supplied by the system.

14. 14 Online travel agency Physical Entity: Computer Customer Conceptual Entity: Travel Vacation Lexical Entity: Itinerary

15. 15 Online travel agency - Connection domain Internet

16. 16 Online travel agency - Cause and effect chain Event: Customer searches for a travel. Events that may happen anyway: Nothing is selected by the customer. Stimulus: Customer gets a list of travels. Response: Customer gets a list of travels. Action: Customer selects a travel.

17. 17 Online travel agency - Cause and effect chain Event: Customer selects a travel. Stimulus: Customer selects a travel for booking. Response: Customer gets a confirmation or a decline. Action: Other connected systems are consulted and customers itinerary is stored.

18. 18 Online travel agency - Requirements Must be reusable. Must be simple to use (not an expert system). Must be higly interactive and guiding to take the place of a sales person (travel agent).

19. 19 Online travel agency- Constraints The system can not foresee last minute changes or delays.

20. 20 Online travel agency We choose the online travel agency. The system displays the following characteristics of a reactive system (cf. [Wieringa, Fig. 1.1]): Highly interactive: Yes, it is always online and it is always possible to book travels at any time. Nonterminating process: Yes, it is always online else it is in a failure state. Interrupt-driven: Yes, responds to requests as they are made. State-dependent response: Yes, depends on the availability of the request.

21. 21 Online travel agency Environment-oriented response: Yes, the system for the most parts relies on responses from other systems. Parallel processes: Yes, many itineraries that are independent from each other. Stringent real-time requirements: Yes partly, able to respond to requests that need be fulfilled now.