A view, consistent with ('satisfying') a Description, on a set of entities. It can also be seen as a 'relational context' created by an observer on the basis of a 'frame' (i.e. a Description). For example, a PlanExecution is a context including some actions executed by agents according to certain parameters and expected tasks to be achieved from a Plan; a DiagnosedSituation is a context of observed entities that is interpreted on the basis of a Diagnosis, etc. Situation is also able to represent reified n-ary relations, where isSettingFor is the top-level relation for all binary projections of the n-ary relation. If used in a transformation pattern for n-ary relations, the designer should take care of adding (some or all) OWL2 keys, corresponding to binary projections of the n-ary, to a subclass of Situation. Otherwise the 'identification constraint' (Calvanese et al., IJCAI 2001) might be violated.