Laying the Foundations for a Formal Theory of Drama

The goal of this research is to lay the foundations for a formal theory of drama, that abstracts from the procedural and interactive aspects involved in the generation of dramatic content. The theory characterizes dramatic qualities by reconciling the structural accounts provided by traditional drama analysis with an agent-based perspective on characters. 1 Motivations and Formalization In the design of AI systems for communication and entertainment, much attention has been devoted to the dramatic qualities exhibited by interactive applications. Typical applications span from artificial characters for entertainment and instruction, to interactive systems for storytelling and drama [1,2,3]. The aim of this paper is to lay the foundations of a formal theory that systematizes the basic aspects of drama in a direct and explicit model, with an immediate integration with agent-based theories. The theory, called Drammar, abstracts from the interactive and procedural aspects of drama generation, and is intended as the starting point for specifying, implementing and evaluating practical storytelling systems in a principled way. The notions of direction, character and plot, pervasive throughout the literature on drama analysis since Aristotle, are the three main components of the drama ontology incorporated in Drammar. The goal of a drama is to make audience perceive what is intuitively called a “story” by displaying the actions of some characters in conflict; actions are organized in a plot; the plot moves toward a direction. Concerning the structure of drama, it has been a well known convention to segment the list of actions that form a drama into a number of units or sections [6]. Such units, despite terminological disparities, are of the same nature, so that some authors define drama as a recursive or “fractal” structure [7]. Drammar is structured in two levels: the actional level models the intentional behaviour of the characters in a plot as intelligent, goal-directed agents. The directional level accounts for dramatic meaning, abstracting from the intentionality of the characters through the use of attributes that model the effect of plot incidents onto the characters’ rational and emotional state. The drama direction is a change function that transforms the rational and emotional state of a character into a different state [4]. Such states are defined through values assigned to a number of attributes of the characters (or dramatis personae), defined as a set of attributes. The set of attributes defining a character combines a rational, BDI perspective with an emotional component. S. Bandini and S. Manzoni (Eds.): AI*IA 2005, LNAI 3673, pp. 286–289, 2005. c © Springer-Verlag Berlin Heidelberg 2005 Laying the Foundations for a Formal Theory of Drama 287 A Dramatis persona CHAR is a pair 〈ATT, POLARITY 〉, where ATT is a subset of a POOL of attributes; POLARITY is a set of pairs 〈x, vx〉, where x ∈ ATT e vx ∈ {+,-}. All the attributes in ATT are assigned a value in POLARITY and for each attribute only one assignment is permitted. The Direction is a function D that specifies the value changes of the characters’ attributes after the execution of the plot. So, the domain of the direction function is a State (where a State is a set of Polarities of attributes), and the co-domain is another State. So, let a State be ⋃ i CHARi.POLARITY : D : Statei → Statef The relationship between the value changes of the rational/emotional states of the characters and the actual actions and events listed in a drama is stated at the actional level through the notion of drama goal. The drama goal is the world state that realizes the Direction, and it is operatively specified as the achievement or the negation of the goal of a certain character, namely the drama protagonist. The Plot is the component that carries out the polarity inversions described by the Direction function. The Plot is a sequence of elementary units called called Beats, pure actional units formed by a action-reaction pair [6]. Notice that some Beat may not change any attribute value, but every change does occur in some Beat. The three components described above form a Drama-unit, that represents by itself all the basic aspects of drama. Formally, a Drama-unit is a triple: – Dramatis personae is a finite set of Dramatis persona; – Direction is a function D defined as above; – Plot is a list of Beats 〈B1, B2, . . . , Bm〉, and the condition holds that at least one attribute inverts its polarity. In Drammar, drama-units are subdivided into smaller drama-units, resulting in a tree of drama-units. The leaves of this tree are directly connected to beats, and its root is the properly called drama, the highest-level unit that subsumes the entire sequence of beats, and is not subsumed by other drama-units. The units of the drama and their directions are combined in a drama-specific progression related with the emotional engagement of the audience via the protagonist’s fate. Dramatic actions in the plot trace a curve related to the fulfilment of the direction. Each drama-unit, with its goal, has both a temporal position and a dramatic value within the plot. This value is given by the number of value changes that occur within the unit, either in a beat directly included by the unit or in a beat included in one of its sub-units.