Page 240 - Socially Intelligent Agents Creating Relationships with Computers and Robots

Towards Integrating Plot and Character 223

which a single agent is facilitating a task, such as instructing a student ([9]),
or giving a presentation ([6]), or in entertainment applications in which a user
develops a long-term relationship with the characters by "hanging-out" with
them ([1]). But for believable agents used as characters in a story world, strong
autonomy becomes problematic. Knowing which action to take at any given
time depends not just on the private internal state of the agent plus current
world state, but also on the current story state, including the entire past history
of interactions building on each other towards some end. The global nature
of story state is inconsistent with the notion of an autonomous character that
makes decisions based only on private goal and emotion state and local sensing
of the environment.
Only a small amount of work has been done on the integration of story
and character. This work has preserved the strong autonomy of the characters
by architecturally dividing the responsibility for state maintenance between
a drama manager, which is responsible for maintaining story state, and the
believable agents, which are responsible for maintaining character state and
making the moment-by-moment behavior decisions ([16]; [2]). These two
components communicate via a narrow-bandwidth, one-directional interface
flowing from drama manager to agent. The messages sent across this interface
consist of goals that characters should assume or perhaps specific actions they
should perform. The character is still responsible for most of the decision
making.
This architecture makes several assumptions regarding the nature of interac-
tive drama and believable agents: drama manager decisions are infrequent, the
internal structure of the believable agents can be reasonably decoupled from
their interaction with the drama manager, and multiple-character coordination
is handled within the agents. Let’s explore each of these assumptions.
Infrequent guidance of strongly autonomous believable agents means that
most of the time, behavior selection for the believable agents will occur locally,
without reference to any (global) story state. The drama manager will intervene
to move the story forward at specific points; the rest of the time the story will
be "drifting," that is, action will be occurring without explicit attention to story
movement. Weyhrauch ([16]) does state that his drama manager was designed
for managing the sequencing of plot points, that is, for guiding characters so
as to initiate the appropriate next scene necessary to make the next plot point
happen (whatever plot point has been decided by the drama manager). Within
a scene, some other architectural component, a "scene manager," would be
necessary to manage the playing out of the individual scene. And this is where
the assumption of infrequent, low-bandwidth guidance becomes violated. As
is described in the next section, the smallest unit of story structure within a
scene is the beat, a single action/reaction pair. The scene-level drama manager
will thus need to continuously guide the autonomous decision making of the