Information Technology Reference
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A set of tales-denominated Previous Stories-forms the material used to create the
structures representing MEXICA's knowledge and experience. The format employed
to define the Previous Stories is Character-1 Action Character-2, e.g. Jaguar Knight
kills Tlatoani. That is, MEXICA does not employ natural language; so, a story is
defined as a sequence of actions performed by characters. The purpose of the Previous
Stories is to provide information about how the world works; they are considered as
well constructed narratives and the user decides their number and topics. Like in the
case of the Dictionary of Story-Actions, the Previous Stories allow expressing some
cultural characteristics. These characteristic will be illustrated in the next section.
13.2.2 Construction of the Knowledge-Base
Employing the dictionary of story-actions and the Previous Stories, MEXICA creates
three types of knowledge structures: Abstract Representation, Tensional Represen-
tation and Concrete Representation.
The Abstract Representation encodes part of the knowledge necessary to retrieve
an appropriate following action during story development. To build these structures
MEXICA performs a detailed analysis of the Previous Stories: for each action in
each tale MEXICA gets the actual Story-Context, re-represents such a context in
more abstract terms (all characters are substituted by variables) and stores it in mem-
ory as a new structure known as Contextual-Structure; finally, it is linked to the
following action performed in the tale. In this way, MEXICA establishes a relation
between Contextual-Structures (abstract representations of story-world contexts) and
logical next actions to be performed. If we employ again the imaginary plot where
Princess suffers an accident and then Jaguar knight heals Princess, the process to
build a Contextual-Structure works as follows. After action 1 is performed the system
updates the Story-Context registering the tension “The life of Princess is at risk”.
Then, the system re-represents the context by substituting the character Princess for
the variable A; so, the Contextual-Structure records “The life of character A is at
risk”. Finally, the next action in the story, in this case Jaguar knight heals Princess, is
linked to such a structure and characters are also substituted by variables. In this way,
the system registers that when the life of character A is at risk, something logical to
do is that Character B heals A (where A and B are variables that can be instantiated
by any character). This process is repeated until the story ends. The same sequence of
steps is repeated for each of the previous stories. Contextual-Structures are employed
during plot generation to progress a story.
The use of emotional links and tensions as a way to organize knowledge pro-
vides a great flexibility. For instance, picture a Previous Story that includes a scene
where Jaguar knight fancies Princess and then he serenates her; now, imagine another
tale where Jaguar knight fancies Princess and then he feels intimidated by her and
runs away. MEXICA records in its knowledge base that when a character A fancies
character B, some logical actions to perform are that A serenates B or that A feels
intimidated and runs away from B. That is, the same context can offer different—and
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