Rules of UML
Well formed models — semantically self-consistent and in harmony with all its related models.
Semantic rules for:
Names — what you can call things.
Scope — context that gives meaning to a name.
Visibility — how names can be seen and used.
Integrity — how things properly and consistently relate to one another.
Execution — what it means to run or simulate a dynamic model.
Avoid models that are
Elided — certain elements are hidden for simplicity.
Incomplete — certain elements may be missing.
Inconsistent — no guarantee of integrity.