If
one of the time units was blinking in that State, the abbreviation of the time unit was
206 DIGITAL WRISTWATCH
shown with four short rays pointing outward. For the Start and Stop States, we chose
the familiar representations of a ?¬?lled circle and a ?¬?lled circle within a hollow circle.
Buttons clearly had a physical counterpart, but also a fairly standard pictogram of the
edges of a stylized three-dimensional button. As the physical counterparts on actual
watches tend to be very small, we used the pictogram. For the Alarm we drewa yellow
bell shape, using a smaller red version of it as a symbol for the special Alarm
Transition relationship. Time variables lacked a clear visible counterpart, but were a
familiar concept from several generic modeling languages; in the end, we chose the
Data Store symbol from Data Flow Diagrams.
An important part of any modeling language is the ?¬‚ow of control or
information, which is normally indicated by arrowheads on the role lines. We thus
placed arrows on the lines from a Button to the Transition it triggered, from the
Transition to the Action it executed, and from the Transition to the State it ended
up in. As the last of these was the most important element of ?¬‚ow in the whole
modeling language, it was shown most visibly, with a dark red ?¬?lled arrowhead.
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