States

  In addition to actions, a variety of states are representable within this knowledge scheme. There are two forms to the states which are represented in the knowledge system. First, states can simply indicate that there is a relationship between other objects in the knowledge structure. Consider the Zoo spaceship. The concepts of spaceship and hugo are related by the state owner-of. Thus, there needs to be a frame in the system which captures this concept, as shown in Figure 8. Each state which acts only as a relation merely contains two   primary attributes, a domain and a co-domain.

  

Figure 8: Partial representation of the owner-of state relation

The other form of state which is representable are descriptions of objects which act to enable or stop various actions from occurring. For example, in Figure 9, the state concept of alert is shown. For these states, it is necessary to know what actions they have been instrumental in helping to achieve; thus, they contain a participated-in primary attribute. It is also necessary to maintain a link to the entity which contained this state; this is accomplished through the object attribute.

  

Figure 9: Partial representation of the alert state