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Engagement stops after three actions have been retrieved (this is a parameter
modifiable by the user) or when an impasse is declared.
The model includes a crucial feature that allows generating novel and interesting
narratives: the possibility of matching a Contextual-Structure that is equal or similar
to the current Story-Context (see step 2 of the engagement cycle). If MEXICA only
matches Contextual-Structures that are equal to the current Story-Context then the
output will be a plot that already exists in the Previous Story. That is, the system
only reproduces (“remembers”) what it already knows. If MEXICA only matches
Contextual-Structures that are vaguely similar to the Story-Context the resulting story
probably will be original but incoherent. Thus, the key is to find a balance between
these two poles. MEXICA includes routines that manage this situation; they allow
matching structures that are similar enough to the Story-Context in order to keep the
coherence of the tale and at the same time retain the flexibility of the process. This
characteristic allows MEXICA to produce sequences of actions that are original but
also relatively consistent, like in a daydream style. During reflection the system fixes
all incongruous situations produced during engagement. Thus, it is important that
the agent's knowledge base includes several similar Contextual-Structures because
in that way the system has more options to produce novel and interesting plots.
So, if the agent's experience is rich the system has more possibilities of generating
appealing outputs.
13.2.3.2 The Reflective State
During Reflection MEXICA performs the following tasks:
1. Evaluation of novelty and interestingness of the material produced during
engagement.
2. Verification of the coherence.
3. If necessary, breaking an impasse triggered during engagement.
(1) During reflection MEXICA evaluates two aspects of the material produced dur-
ing engagement: novelty and interest. Each time MEXICA performs an evalu-
ation the guidelines are updated. Guidelines can be pictured as messages sent
from the Reflective State to the Engaged State that attempt to contribute to the
generation of novel and interesting narratives.
A story is considered novel when it is not very similar to any of the tales in
the file of Previous Stories. If the system detects that the story in progress is too
similar to any of the Previous Stories the novelty-guideline can be set as follows:
“during engagement only employ actions that have not been used frequently in
the previous stories” (c.f. Turner [ 9 ]).
A story is considered interesting when it includes, at least, an introduction,
climax and resolution (see Fig. 13.1 ); so, in order to assess the interestingness
of the story in progress MEXICA analyses its Tensional Representation. For
instance, if the story in progress is too “flat” and it is necessary to increase the
Tension to the reader the following interestingness-guideline can be set: “during
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