UMLR — UML: Add abilities to specifiy intent of Assert, Negate, Consider, Ignore fragments

In sequence diagrams the use of Assert, Negate, Consider, and Ignore fragments often leaves the reader confused about their intent.

For example, an Assert fragment is intended to mean that this fragment is the only sequence of events to be considered. This could be interpreted as the only sequence

1) that can occur; so the reader/developer does not need to consider others as they are impossible

2) that is interesting; so that the reader/developer can ignore the others as being not interesting

3) that is allowed; so if something else occurs it is an error

4) that is allowed; so that the reader/developer needs to prevent the others from occurring.

Similar issues arise with the other fragments

An Negate Fragment, could be interpreted as

1) this fragment can never occur, so don’t worry about it

2) If this fragment occurs this is an error

3) You need to prevent this fragment from occurring

These can be solved by adding a parameter to these fragments

e.g., Fact (this is the way it is); Enforce (this is the way we have to make it); Error (violations are errors); Ignore (don’t worry about violations)