Assessment Indicators:
- Ability to translate informal textual system description into formal description
- Ability to justify system design decisions
- Ability to analyze a formal system specification
The following is a description of a smart freezer security system (HAL). Smart freezers are used in labs for storing experimental samples. HAL consists of sensors, actuators and a control system. The following sensors and actuators are present:
- Contamination checkers CCi (0 ≤ i ≤ 1), these can be on or off. CC0 indicates the checker for the top drawer shelf and CC1 the checker for the bottom drawer shelf. The freezer in this scenario has two drawer shelves. When a checker is in mode on, a contamination sensor is activated to analyze the drawer.
- Door sensors Di (0 ≤ i ≤ 1), indicating whether the doors are open or not. The freezer has two doors (one for each drawer shelf).
- Temperature sensor TEMPi (0 ≤ i ≤ 1), indicating whether the temperature inside each drawer is the proper one.
- Switch S, indicating whether one is in the lab or away.
- Alarm A, this can be on or off.
The control system determines whether contamination checkers CC, are on or off and whether the alarm should sound and send an alert text message to the head of the laboratory, depending on the state of the various sensors.
HAL operates in two modes, lab and away. The user indicates this choice by the switch S (this can be a portable wireless switch).
When in away mode, HAL operates as follows:
- Contamination checkers CCi are switched on and off in a pre-selected patter based on the lab policy. This pattern can be set by the user on a per minute basis, away Pat [i] [k] = 1, means contamination checker CCi should be on at time k, 0≤ k < 1440=24*60.
- If at least one of the temperature sensors TEMP, detects an increase of the temperature the alarm A should be activated.
- The user should switch HAL to away mode when all doors are closed otherwise HAL will complain that you cannot switch to away mode.
If HAL is in lab mode, it will operate as follows:
- Contamination checkers are switched on and off in a pattern selected by the user. This pattern can be set by the user on a per minute basis, labPat [i ] [ k] =1, means contamination checker CCi should be on at time k, 0 ≤ k < 1440=24*60.
- The user can set the times when HAL should check door and temperature sensors. These times can be set by the user on a per minute basis, Check [k] =1, means door and temperature sensors should be checked at time k, 0 ≤ k < 1440=24*60.
a) Give a Tempura specification of HAL. Log decisions on how you resolve any ambiguity. Use the following 24-hour scenarios to illustrate your answer with output from your Tempura program:
i) Normal working day at lab: the user works in the lab, sets labPat and Check pattern but HAL does not detect anything wrong.
ii) The forgotten open door: the user finished his experiment, put the samples in the freezer and is about to go away. He/she has set the awayPat pattern. The user presses the switch S to tell HAL to switch to away mode. However, HAL complains that it cannot switch to away mode as the user has forgotten to close the door Do. The user has to close the door and then try switch S again.
iii) A malfunction of the freezer: the user has a day off and is away from the lab all day and sets the awayPat pattern. Suddenly, at 23:40 the temperature sensor TEMPO detects an increase of the temperature inside the freezer and the alarm sounds.
The following marking scheme will be used
Environment: User/Sensors
Tempura +3 scenarios: 10-12
Tempura + 2 scenarios: 07-09
Tempura + 1 scenarios: 03-06
English: 00-02
Controller: HAL
Tempura +3 scenarios: 10-12
Tempura + 2 scenarios: 07-09
Tempura + 1 scenarios: 03-06
English: 00-02
Integration
Tempura: 03-06
English: 00-02
b) The system that you have specified needs to satisfy certain liveness conditions.
Give one example of a liveness condition that your system should satisfy and formulate them in ITL/Tempura.
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