Sommerville-Software-Engineering-10ed

21.2 ■ Architectural patterns for real-time software 621
Figure 21.6 The
Observe and React
pattern
Name
Description
Stimuli
Responses
Processes
Used in
Observe and React
The input values of a set of sensors of the same types are
collected and analyzed. These values are displayed in some
way. If the sensor values indicate that some exceptional
condition has arisen, then actions are initiated to draw the
operator’s attention to that value and, if necessary, take actions
in response to the exceptional value.
Values from sensors attached to the system.
Outputs to display, alarm triggers, signals to reacting systems.
Observer, Analysis, Display, Alarm, Reactor.
Monitoring systems, alarm systems.
Sensors
Display
Observer
process
Sensor
values
Analysis
process
Display
values
Display
process
Alarm
process
Reactor process
Figure 21.7 The
Observe and React
process structure
Alarm
Other equipment
These architectural patterns should be the starting point for an embedded systems
design; however, they are not design templates. If you use them as such, you will
probably end up with an inefficient process architecture. You have to optimize the
process structure to ensure that you do not have too many processes. You also should
ensure that there is a clear correspondence between the processes and the sensors
and actuators in the system.
21.2.1 Observe and react
Monitoring systems are an important class of embedded real-time systems. A monitoring
system examines its environment through a set of sensors and usually displays
the state of the environment in some way. This could be on a built-in screen, on
special-purpose instrument displays, or on a remote display. If the system detects
some exceptional event or sensor state, the monitoring system takes some action.