Why does F. Wagner consider "NOT (AI_LARGER_THAN_8.1)" to be ambiguous?
- by oosterwal
In his article on Virtual Environments (a part of his VFSM specification method) Ferdinand Wagner describes some new ways of thinking about Boolean Algebra as a software design tool. On page 4 of this PDF article, when describing operators in his system he says this:
Control statements need Boolean
values. Hence, the names must be used
to produce Boolean results. To achieve
this we want to combine them together
using Boolean operators. There is
nothing wrong with usage of AND and OR
operators with their Boolean meaning.
For instance, we may write:
DI_ON OR AI_LARGER_THAN_8.1 AND
TIMER_OVER
to express the control situation:
digital input is on or analog input is
larger than 8.1 and timer is over.
We cannot use the NOT operator,
because the result of the Boolean
negation makes sense only for true
Boolean values. The result of, for
instance,
NOT (AI_LARGER_THAN_8.1)
would be ambiguous.
If "AI_LARGER_THAN_8.1" is acceptable, why would he consider "NOT (AI_LARGER_THAN_8.1)" to be ambiguous?
