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Specification of IT Systems Mandatory Exercise Week 1

Group 3

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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.

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Traffic light - Subject domain

• Physical Entity: • Light beacon• Sensor• Road• Car• Button

• Conceptual Entity:• Green light• Red light• Yellow light

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Traffic light - Connection domain

• Sensor

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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.

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Traffic light - Requirements

• Must reliable.

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Traffic light - Constraints

• The system can not physically constrain cars.

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Booking System (DGI)

• 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.

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Booking System (DGI) - Subject domain

Physical Entity: • Computer• Customer• Administrator

• Conceptual Entity:• Session

• Lexical Entity:• Webpage

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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

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Booking System (DGI) - Requirements

• The system must be reliable.

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Booking System (DGI) - Constraints

• The system cannot check for errors by administrators.

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Online travel agency

• 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.

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Online travel agency

Physical Entity: • Computer• Customer

Conceptual Entity:• Travel • Vacation

Lexical Entity:• Itinerary

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Online travel agency - Connection domain

• Internet

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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.

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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.

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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).

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Online travel agency- Constraints

• The system can not foresee last minute changes or delays.

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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.

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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.