1. Heating element Temperature sensor Heating element 220V AC Controller I/O panel

2. Requirements – natural language 1.The user shall be able to use a simple panel to define time intervals, consisting of – Starting time – Ending time – Temperature during this interval – Ta 2.The time intervals are not allowed to overlap 3.The user shall be able to use a simple panel to define a temperature tolerance value d. 4.If the user don't set a temperature tolerance, the system shall use default value d = 2 o C 5.If the temperature falls below Ti – d, the heather shall be turned on 6.If the temperature exceeds Ti + d, the heather shall be turned off 7.If time is outside all defined intervals the temperature shall be set to a predefined default value T0.

3. Requirements – boilerplates 1. shall be able to 2. shall be able to 3. shall be able to 4.If, shall 5. shall have 6. shall have 7. shall have 8.In order to, shall have 9.In order to, shall have 10.If, shall 11.If, shall 12.When, shall 13. shall at least times per 14. shall not allow to 15.If, shall