From MEXICA to MEXICA-Impro: The Evolution of a Computer Model for Plot Generation - Computational Creativity Research: Towards Creative Machines - page 268

13.3 A Computer Model for Plot Evaluation

The engagement-reflection model considers evaluation as an integral part of the
creative process. The current version of MEXICA is capable of performing two
types of assessments: one during plot generation and the other after the story has
been finished. The first of these processes evaluates the story in progress; its purpose
is to contribute to advance the narrative. The second values the final product; its goal
is to determine if the system's output might be classified as c-creative. I refer to a
computer agent that is capable of assessing a final product as Evaluator. This section
describes MEXICA's features as an Evaluator.
MEXICA has the capacity of assessing the narratives it generates or the narratives
generated by other agents, as long as they are represented in terms of sequences of
actions that follow the format employed in the Previous Stories. There are three main
aspects that the model considers:

(1) As explained earlier, I believe that an essential aim of creativity is the generation
of expertise that is useful for the creative process itself. I claim that the same
principle is valid during the assessment of a narrative. Thus, a computer model of
evaluation must consider if the Evaluator, as a result of the assessment it performs,
incorporates new knowledge structures into its knowledge base. Otherwise, what
is the point of considering new material?
(2) As explained earlier, in MEXICA a story is recounted in a correct manner when
it follows the classical Aristotelian structure of a story: development, climax
and resolution (or setup, conflict and resolution). The Tensional Representation
plays a fundamental role in this part of the process because it allows analysing
these characteristics within a plot (see Figs. 13.1 and 13.2 ).
(3) It is necessary to verify if the sequence of actions that comprise a story satisfies
common sense knowledge, i.e. to check if all preconditions are satisfied.

In order to perform the evaluation MEXICA weighs up seven characteristics.
In some cases the process consists in calculating a value for each feature and then

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c)
Climax

b)
Reintroducing
complications

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8

6

d)
Adequate closure

a)
Correct opening

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2

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Actions

Fig. 13.2 Employing the Tensional Representation to evaluate a plot