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meets(Ev_time, Resp_time),
starts_before(Resp_time, Act_time)}.
Figure 1 shows a partial parse tree. The ovals depict non-terminals, and the
rectangle depicts a terminal expression. The grammar specifies the structure
of the tree and the kind of event list expression needed at the leaf nodes. The
expressions at the leaves are instantiated by a separately defined world model.
The implementation
The ambiguity and poor specification of previous narrative models made them
difficult or impossible to implement. This weakened the claim that these mod-
els of narratives were, in fact, computational in nature. We present a concrete
implementation in support of our claim that our model, based on our the-
ory of rational intention in autonomous agents (Goldman & Lang 1993; Lang
1997), is indeed a computational model describing a non-trivial class of narra-
tives. The implementation, named Joseph ( J ust O rdinary S tories E numerated
by P rolog H ierarchically), produces randomly generated natural language nar-
ratives conforming to the-grammar.
Components of Joseph
The tasks of the Joseph story generation system are divided among the follow-
ing components:
Story grammar: At the core of Joseph is the implementation of the-grammar.
The story grammar defines structured series of story components.
Grammar interpreter: The grammar interpreter defines the search strategy of
the generation process. We use depth-first, iteratively deepening search (Korf
1987) plus random choice to find a sequence of grammar rule rewrites which
defines a valid story.
Temporal predicates: The events in a story must satisfy temporal relations
specified in the-grammar. We implement Allen's temporal relations (Allen
1984) to enforce temporal constraints on story components.
Wo r l d mo d e l : A story must have content as well as form. The story grammar
produces abstract representations of stories; the grammar specifies terminals
as schemas but does not specify the bindings of variables contained in those
schemas. The potential instantiations of terminals are drawn from a set of
actions that characters may perform and fluents that vary during the course
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