Represents the scientific goal associated to a SimDM/Resource. This can be the goal of an experiment or project, or the type of object that a particular protocol will always produce. Is made concrete by suclasses representing objects or processes. We model a Target as "being an" ObjectType, which allows one to give a more detailed representation of its properties. The target is important as it represents one of the main questions scientists will ask about an experiment: what kind of astrophysical object or system or process was being simulated or modelled.