Structuring Content in the Façade Interactive Drama Architecture

The process of building Façade, a first-person, real-time, one-act interactive drama, has involved three major research efforts: designing ways to deconstruct a dramatic n arrative into a hierarchy of story and behavior pieces; engi neering an AI system that responds to and integrates the playe r’s moment-by-moment interactions to reconstruct a real -time dramatic performance from those pieces; and underst anding how to write an engaging, compelling story within t his new organizational framework. This paper provides an o verview of the process of bringing our interactive drama to life as a coherent, engaging, high agency experience, includi ng the design and programming of thousands of joint dialog behaviors in the reactive planning language ABL, an d their higher level organization into a collection of stor y beats sequenced by a drama manager. The process of itera tively developing the architecture, its languages, authori al id oms, and varieties of story content structures are descr ibed. These content structures are designed to intermix t o offer players a high degree of responsiveness and narrati ve agency. We conclude with design and implementation lessons learned and future directions for creating more generative architectures. Approaching Interactive Story Stories have rich global, temporal structures whose features can vary both in form and pleasure for audiences. Some stories feature tightly-plotted causal chains of ev ents that may, for example, offer audiences the intrigue of a intricate, unfolding mystery, or the spectacle of a n epic historical conflict. By contrast, some stories hav e sparse, even amorphous event structures, that can offer, fo r example, the quieter pleasure of following the subt le progression of emotion between two people. The his tories of literature, theater, cinema and television demon strate that many types of story structures can be pleasura ble for audiences; the challenge for researchers and artist s is determining how traditional story forms can be adap ted for interactivity. Interactive experiences have several identifiable features of their own, such as immersion, agency, and transformation (Murray 1997), each offering particu lar pleasures for interactors, and varying compatibilit y with story. For many artists and researchers, agency is often Copyright © 2005, American Association for Artifici al Intelligence (www.aaai.org). All rights reserved. considered the holy grail of interactive story plea sures, perhaps because it offers players the most substant ial influence on the overall structure of the experienc e. Agency is also the most challenging to implement, e xactly because it requires the system to dynamically assem ble a story structure that incorporates the unpredictable ctions of the player. This suggests that stories with looser, sparser event structures (plots) will be easier to impleme nt in an interactive medium (require less generativity ), and thus should be a good starting point for interactiv e story researchers and artists. Note that such stories ca n be as pleasurable as tightly-plotted ones, just in differ ent ways. When designing an interactive story architecture a nd its content structures, the design choices made will in flue ce the types of stories that can be built within it, a nd greatly affect the likelihood of ultimately creating pleasu rable experiences for players. With this in mind, the Façade architecture was designed with features intended fo r building experiences with igh agency , and with enough narrative intelligence (NI) (Mateas and Sengers 200 2) to construct character-rich, causally-sparse yet coher ent plots. Further, we chose to implement several NI features particular to theatrical drama, a powerful story form historically shown to be compatible with sparse plo ts, compensated for by rich emotional expression from its characters. Additional features therefore importan t to support include characters with a strong sense of immediacy and presence , whose very aliveness results in the audience experiencing a sensation of danger or unpredictability, that anything is possible. This paper presents Façade’s solution to the tension inherent between game and story, some organizing principles allowing us to move away from traditiona l branching narrative structures, and an overview of Façade’s architecture, combined with how its content is structured and applied. We describe Façade’s atomic unit of dramatic performance, the joint dialog behavior, the variety of its applications within the drama, their organization into story beats that afford sparse bu t coherent plots, and their integration with sets of forward-c haining natural language processing (NLP) rules offering pl ayers a high degree of emotional expression. We conclude w ith design and implementation lessons learned, and futu re directions for creating more generative architectur es. All of this discussion is guided by our primary design goal: to create an architecture for, and working example of, high agency, emotionally expressive interactive drama. Resolving Game Versus Story Today’s most pleasurable high agency interactive experiences are games, because the mechanics of gam e agency are well understood and reasonably straightf orward to implement. Player moves such as running, jumpin g or shooting, playing a card, or moving a pawn directly ause scores, stats, levels or abstract game-piece config urat ons to change. (Simulations of physical environments a nd resource-bound systems have more complex state, but can still be represented numerically in understood ways .) However, to date, a high agency interactive story h as yet to be built. Existing game design and technology appro aches, that focus on the feedback loop between player inte ac ion and relatively simple numeric state, seem inappropr iate for modeling the player’s effect on story structure, whose complex global constraints seem much richer than ca n be captured by a set of numeric counters or game piece s. Our solution to this long-time conundrum is to rec ast interactions within a story world in terms of abstr act social games. At a high level, these games are organized around a numeric “score”, such as the affinity between a cha racter and the player. However, unlike traditional games i n which there is a fairly direct connection between player interaction (e.g. pushing a button to fire a gun) a d score state (e.g. a decrease in the health of a monster), in our social games several levels of abstraction may sepa rate atomic player interactions from changes in social “ score”. Instead of jumping over obstacles or firing a gun, i Façade players fire off a variety of discourse acts , in natural language, such as praise, criticism, flirta tion and provocation. While these discourse acts will genera te immediate reactions from the characters, it may tak e storycontext-specific patterns of discourse acts to infl uence the social game score. Further, the score is not direct ly communicated to the player via numbers or sliders, but rather via enriched, theatrically dramatic performa nce. As a friend invited over for drinks at a make-or-b reak moment in the collapsing marriage of the protagonis ts Grace and Trip, the player unwittingly becomes an antagonist of sorts, forced by Grace and Trip into playing psychological “head games” with them (Berne 1964). During the first part of the story, Grace and Trip interpret all of the player’s discourse acts in terms of a ze ro-sum affinity game that determines whose side Trip and Grace currently believe the player to be on. Simultaneous ly, the hot-button game is occurring, in which the player can trigger incendiary topics such as sex or divorce, progressing through tiers to gain more character an d backstory information, and if pushed too far on a t opic, affinity reversals. The second part of the story is organized around the therapy game , where the player is (purposefully or not) potentially increasing each characters’ deg re of self-realization about their own problems, represen ted internally as a series of counters. Additionally, the system keeps track of the overall story tension level , which is affected by player moves in the various social game s. Every change in each game’s state is performed by G race and Trip in emotionally expressive, dramatic ways. On the whole, because their attitudes, levels of self-awar eness, and overall tension are regularly progressing, the expe rience takes on the form and aesthetic of a loosely-plotte d domestic drama. Figure1. Grace and Trip in Façade, viewed from the player's first-person perspective. Richness Through Coherent Intermixing Even with a design solution in hand for resolving t he tension between game and story, an organizing princ i le is required to break away from the constraints of trad i ional branching narrative structures, to avoid the combin atorial explosion that occurs with complex causal event cha ins (Crawford 1989). Our approach to this in Façade is twofold: first, we divide the narrative into multiple fronts of progression, often causally independent, only occasionally interdependent. Second, we build a variety of narrative sequencers to sequence these multiple narrative progressions. These sequencers operate in parallel and can coherently intermix their performances with one ano ther. Façade's architecture and content structure are two sides of the same coin, and will be described in tandem; along the way we will describe how the coherent intermixi ng s achieved. Architecture and Content Structure The Façade architecture consists of characters written in the reactive-planning language ABL, a drama manager that sequences dramatic beats, a forward-chaining rule s ystem for understanding and interpreting natural language nd gestural input from the player, and an animation en gine that performs real-time non-photorealistic rendering, sp oken dialog, music and sound, driven by and providing se nsing data to th