Defacto

IRIS Wiki - IS Systems - Defacto

Availability

Webpage of the Defacto European project (97-98)

Technical Description

Defacto is an interactive story generation system, where the user intervenes in the story by choosing between options for the story protagonist.

The story generation uses Artificial Intelligence techniques to generate characters' actions, based on a set of rules. The algorithm contains two phases:

• Dramatic sequence generation
• Resolution

In the first phase, a sequence of actions is dynamically generated, with user intervention, until no dramatically interesting interaction is found. In the second phase, the current actions' outcomes are computed to provide an unambigious solution to the story. This resolution follows an aristotelian organization of drama.

Dramatic sequence generation

The story actions are generated in two steps.

• in a first step (called "generation"), a set of possible interactions between the story characters is generated, according to both their goals and norms. Characters not only perform their own goals but can also intervene, favorably or unfavorably, in other characters' goals. Social interaction also occurs, for example a character helping another character if they were helped by this character in the past.

One particular action will be generated for each character. In order to select which action each character could perform, the following selection rule is used: Choose the action that refers to as much of the story background as possible.

• In a second step (called "evaluation"), interesting dramatic situations are detected, according to a series of dramatic-related rules, such as:
  • User-Centered Drama: Select an action that involves the protagonist for the next plot development
  • Interactivity bias: Favor user participation in the story
  • User-Centered Engagement: Favor a protagonist's goals for the current storyline goal
  • Unity of Plot: Accept intervention by characters affiliated with the current storyline goal
  • Parsimony of Plot: limit the number of actions related to a conflict between two characters (to avoid infinite sequence of reciprocal interactions between two characters)

Resolution

Following the classical aristotelian arc, the plot manager refrains from resolving any action attempt before resolution. The start of resolution corresponds to the main climax of the drama. Resolution consists in deciding which actions succeed and which actions fail, including user actions.

Resolution is based on a succession of decision rules, in which actions are resolved. These rules depend on the author's choice of favoring users' goals over norms, or vice-versa.

Suspense is generated when all the attempts by other characters to make the user succeed, fail, but then in the end, the user's action finally succeeds (vice versa if the user's action is to fail).

Result Description (end user perspective)

The prototype implements a greek tragedy, involving various characters with their goals and conflicts. The goal of the user is to worship Poseidon in Corinthos. The story happens in a 3D environment. At important moments in the narrative, the user is given options to choose from.

Authoring Description

No authoring tool or approach is detailed. From the technical description, it can be deduced that authoring requires defining characters, goals, norms, and tuning of several parameters of the Artifical Intelligence algorithms.

Strong Points

Defacto is highly generative, thus providing a potential solution to the core algorithmic issue of interactive storytelling (narrative paradox). This system truly incorporates in its mechanics both strong narrative consraints and user-centered constraints. The system has been fully implemented.

Limitations

The complexity of the algorithms makes its appropriation by other researchers and authors difficult.

Main Publications

Sgouros, N. M.(1999). Dynamic Generation, Management and Resolution of Interactive Plots, Artificial Intelligence, 107,1, 29-62.

Supporting Narrative Theories

Defacto is explicitely based on the theory of Aristotle.

Defacto implements norms, wich corresponds to the ethical dimension of narrative.

It is also partially based on the idea of increasing the suspense (in the Resolution phase).

Computational Model

First Order Logic.

Type of interaction

The story is represented in a 3D environment, while user interaction occurs via multiple choice menus.