Negative (Combined Fragment)   A negative interaction operator (signified by the value of neg) defines a combined fragment where the enclosed traces are all invalid. The operator is used to express the fact that the traces cannot occur. By implication any traces not enclosed in the negative interaction operator are valid. A combined fragment with a negative operator can have one (and only one) operand.

Explanation

The negative operator is used to define a set of traces that cannot occur. It is used when it is important to express the fact that one or more traces are not permitted to happen and the modeler wants to draw attention to this fact. In our everyday life we often come across this concept. For example when a media company runs a public competition it will often state that employees and their families are not permitted to enter the competition. There is no programming level equivalent other than a comment in the source code stating that certain calls are not permitted.

Related Entries

Assert (Combined Fragment)  Graphically Similar,  Similar Usage A combined fragment with an operator of assertion (assert) is related to a combined fragment with an operator of negative (neg) because if the set of traces defined by the assertion operator do not occur exactly in the sequence indicated the entire set of messages are considered to be invalid.