Figure 4. Object groups are spatially scattered fiat entities.

An object group is an aggregate of objects in which the objects (here shown in dark grey) are separated from each other by space or, like in the case depicted, by other objects (shown in light grey), with which they can even form an object cluster. Every object group is demarcated by a combination of bona fide boundaries and fiat boundaries^immat. The example depicted could represent the distribution pattern of sensory cells (i.e. sensory cell group) within an epithelial cell cluster, in which the sensory cells (dark grey) are part of the sensory cell group as well as of the epithelial cell cluster. Fiat boundary ^immat : demarcates fiat parts of an immaterial entity (i.e. a hole).