Represents the authority for some bit of decision logic.  Have no executable semantics Represents a self-contained bit of business logic.  Its value expression is a function definition, an expression of it parameters.  A decision invokes a BKM by mapping its inputs to the BKM parameters; the BKM output value is then returned to the invoking decision Represents data values received at the time of execution.  Input data has not value expresssion. Represents an output value or values for a given set of Input values.