Hi, On 26 Oct 2010, at 14:47, Fabrizio Perin wrote: This kind of things are always a problem with single inheritance. In this case, I cannot think of a case in which we can annotate other entities except sourced entities. So, it should indeed be fine to move the property down into FAMIXSourcedEntity. derived means it can be derived from another piece of information. When you have a bi-directional association, derived most always means that it can be derived from the other end of the association. Typically, when we have a 1-to-n association, we mark the n end with derived. In this case FAMIXAnnotationInstance>>annotatedEntity is not derived, but FAMIXEntity>>annotationInstances is derived. Cheers, Doru -- www.tudorgirba.com "In a world where everything is moving ever faster, one might have better chances to win by moving slower."