4 2 4 A perceptual, cognitive and communicative system. This represents a cogntive process rather than a physical being. It represents a conscious entity and therefore cannot be directly experienced from within the universe of discourse, it itself is the one who experiences. It can however be indirectly experienced by communicating with it. It produces representations and it can observe representations, hence, with the right code you can communicate with it. So the representations are directly observable but the conscious entities are only indirectly observable through communication. 4 An object within the universe of discourse. An object is something that can be experienced as an observable and thereby conceptualised then represented within a universe of discourse. Any object within the universe of discourse can be experienced as an observable. Classes such as pccSystem and pccInteraction are not objects, hence they are 'invisible' to the universe of discourse.