Entity (owl:Class) Anything: real, possible, or imaginary, which some modeller wants to talk about for some purpose.

Situation (owl:Class) A view on a set of entities. It can be seen as a 'relational context', reifying a relation.

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:

- creating only one situation for each instance of an n-ary relation, otherwise the 'identification constraint' (Calvanese et al., IJCAI 2001) could be violated

- adding an 'exact cardinality' restriction corresponding to the arity of the n-ary relation, otherwise the designer would actually represent a polymorphic relation.

hasSetting (owl:ObjectProperty) A relation between entities and situations, e.g. 'this morning I've prepared my coffee with a new fantastic Arabica' (i.e.: (an amount of) a new fantastic Arabica hasSetting the preparation of my coffee this morning).