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the relationships among the characters, events, actions, effects, emotions, and
goals appearing in arbitrarily selected Russian folk tales.
During generation, the world model instantiates the grammar terminals.
For example, two terminal components of an episode are an event and the
protagonist's reaction to that event. However, the grammar specifies neither
the event nor the reaction. To instantiate these components, the grammar in-
vokes the world model, which specifies possible events and character reactions.
The list of instantiated terminals (i.e. states and events), up to the point of the
world model invocation, is available to the world model predicates so that these
predicates can check preconditions of relations and bind variables to domain
elements mentioned in the story.
A story grammar is independent of the world model. In other words, the
story grammar does not require any particular means of providing an event,
state, reaction, etc. The Joseph system's world model is implemented as sets
of associations between events and their effects, emotions and the actions that
arise out of them, goals and the actions which serve them, states and conse-
quences of those states, etc. We refer to these associations collectively as the co-
herence predicates. Each association is expressed in general terms as the head
of a prolog clause, the body of which describes the conditions that make the
association compatible with the events and states of a partially generated story.
When a world model predicate is encountered during generation, the grammar
interpreter collects all such compatible associations and chooses one at random
to instantiate the grammar terminal expression.
The coherence predicates do not specify individual domain elements such
as a character, place, object, etc. These atomic domain elements are abstracted
out of the coherence predicates and specified separately along with their at-
tributes. This allows the coherence predicates to be expressed in general terms.
For example, one coherence predicate associates a character's seeing a desirable
thing with the character's adopting the goal of having that thing, without saying
what the thing might be. Separating the coherence predicates from the domain
elements and their attributes enables easier modification and maintenance of
the world model and simplifies addition of both new coherence associations
and new atomic domain elements.
Output samples
This section presents selected stories generated by this implementation. The
simplest possible story in our model consists of a setting followed by a single
