It can be asserted about any variable or constant in the structure that it
|Does Not Exist|
The Default setting for creating the model may be DoesExist, represented as True, or MayExist, with a value of 0.5. With MAY_EXIST, a range of 0 to 1.00 is permissible, so it behaves similar to Bayesian logic. A value of 0.5 implies no information about existence. If existence is asserted on a variable, this existence value is propagated along the links connected to it. An object with attributes which has its existence value changed, will propagate the change to its attributes and to its class. Either the attributes or the class may reflect a value of UKE 0.5, turning the object off again, and also turning off the path which caused the excitation of the object.
The existence property is orthogonal to logical state, and precedes it in evaluation - the system must know the existence before evaluating the state.
The normal connectives of Boolean logic - AND, OR, XOR, NOT, EQV - can be used with existence logic.
This logic of existence is particularly useful with objects, but is also applicable to all other variables, so that numeric variables, for example, can be made to disappear, taking their values with them (and having PLUS, etc. behave appropriately).
ASSOCIATE - association can be based on values, or dynamically determined
ATTRIBUTES - objects have attributes, which are excited by the object
BOOLEX - translates between Boolean and Existence logic
CAUSE - the existence of an object causes existence of another
CHECKEXIST - attributes are checked for some condition
EXISTS - provides existence link from object
MEMBERS - provides class hierarchy
SUPPORTS - an object's presence is required, rather than as cause