truth values if one variable is undefined?

From: Ernst Murnleitner (mur@awite.de)
Date: Mon Mar 25 2002 - 13:12:15 MET

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    Dear readers,

    I want to handle undefined variables, i.e. if a measurement ist not
    available and thus the input value is invalid:

    In our software, we set a flag "invalid" to true, if the measurement is not
    available.
    But there comes up the following question: How should the term with the
    undefined variable be handled?
    One possibility would be, to let the truth always be "0" of that sub-term,
    e.g.:
    IF A = a THEN ...
        ####
        Here, (A=a) = 0

    But how should NOT be handled then?

    IF (NOT(A=a)) THEN
          #########
          Here, (NOT(A=a)) would be "1"!

    Or should the complete subterm with the undefined variable be "0"? Hence,
    NOT(A=a) would be "0".

    (To Invalidate the whole rule, Is not a good idea: because: IF A=a OR B=b
    THEN ...)

    Greetings
    Ernst Murnleitner

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