Usage of the terms "source" and "target" imply a meaning
that is beyond that defined in UML v1.4 where the terms
are simply relative to the end being discussed at the time.
Some parts of clause 7.2 seem to imply that an
association always has a fixed target end and a fixed
source end. This may be how UML is implemented in one
tool but conflicts with usage in the standard.
Clarify usage of "source" and "target".
Fixed in version 2.1.