An actor might be either a simple physical entity such as a doctor, a dog, a bicycle or tree a more complex physical entity, e.g. city, forest, people an immaterial entity, e.g. ideas or concepts such as politics an adjective, e.g. beautiful, old, tall, nice a verb or description of doing or going on, e.g. talking, running, hugging Actor objects have representations of their own. Compound objects are basically groups of objects. Compound objects have no representations themselves. Realizing compound objects is done by realizing the objects they consist of. See further discussion in Section 4.1 .
Relations are objects which establish a relationship between objects.
A relation contains a set of describing objects. A relation defines a relationship which has its origin in the set of source objects. The objects affected by that relationship are the destination objects. The type of the relationship is defined by the set of describing objects. Note that objects may appear in either set, which means that bidirectional relationships are possible as well.