An Oz−Centric Review of Interactive Drama and Believable AgentsMichael Mateas June 1997 CMU−CS−97−156School of Computer Science Carnegie Mellon University Pittsburgh, PA 15213AbstractBelievable agents are autonomous agents that exhibit rich personalities. Interactive dramas take place in virtual worlds inhabited by characters (believable agents) with whom an audience interacts. In the course of this interaction, the audience experiences a story (lives a plot arc). This report presents the research philosophy behind the Oz Project, a research group at CMU that has spent the last ten years studying believable agents and interactive drama. The report then surveys current work from an Oz perspective.This research was partially supported by a grant from Intel Corporation. The views and conclusions contained in this document are those of the author and should not be interpreted as representing the official policies, either expressed or implied, of Intel Corporation.Keywords: artificial intelligence, art and entertainment, believable agents, interactive drama, Oz.A note on formattingThis document was originally formatted using HTML. The postscript version was produced by printing to postscript from an HTML editor. Internal links between the report and the bibliography have been turned into citations. Links in the bibliography to other sites have been turned into lists of URLs. The more natural hyperlinked version of this document can be found at http://www.cs.cmu.edu/afs/cs.cmu.edu/project/oz/web/papers/CMU−CS−97−156.html. Please send any comments to [email protected]. IntroductionThis report provides an overview of research in believable agents and interactive drama. Many of the original sources used in compiling this report can be found on the web; the annotated bibliography provides links to these web resources. This report unabashedly surveys its topic with the bias of the Oz project [Oz] at CMU. The reason for this is threefold. First, I am a member of this research group and have internalized much of their perspective; I won’t pretend not to have a viewpoint. Second, there is not much work that is directly related to interactive drama and believable agents; using the Oz project as a center allows me to make sense of more peripheral work. Finally, Oz is the only group giving equal attention to both character (believable agents) and story (interactive drama); an Oz perspective allows me to present character and story as a unified whole. For much of the content of this report, I am indebted to the members of the Oz project: Joe Bates, Bryan Loyall, Scott Neal Reilly, Phoebe Sengers, and Peter Weyhrauch. Much of my understanding grew out of conversations with them. In particular, the Oz philosophy, which is described below, was developed by the group during 10 years of research. The first item of business is to define the research goal for believable agents and interactive drama: building worlds with character and story. Drama = Character + Story + PresentationArtists building non−interactive dramas (e.g. movies, books) have commented on the importance of both character and story for authoring powerful, dramatic experiences. For example, Lajos Egri, in the Art of Dramatic Writing [Egri 46], has this to say about premise (i.e. plot or story)."No idea, and no situation, was ever strong enough to carry you through to its logical conclusion without a clear−cut premise. If you have no such premise, you may modify, elaborate, vary your original idea or situation, or even lead yourself into another situation, but you will not knowwhere you are going. You will flounder, rack your brain to invent further situations to round out your play. You may find these situations − and you will still be without a play." Later, in talking about character, he defines three dimensions every character must have: physiology, sociology and psychology. He has this to say about these three dimensions: "Analyze any work of art which has withstood the ravages of time, and you will find that it has lived, and will live, because it possesses the three dimensions. Leave out one of the three, and although your plot may be exciting and you may make a fortune, your play will still not be a literary success.When you read drama criticisms in your daily papers, you encounter certain terminology time and again: dull, unconvincing, stock characters (badly drawn, that is), familiar situations, boring. They all refer to one flaw − the lack of tridimensional characters."Figure 1, below, shows the high level architecture of the Oz project. This architecture arose out of a desire to treat character and story in interactive drama as seriously as do dramatic artists in traditional media. Fig. 1 A simulated world contains characters. These characters exhibit rich personalities, emotion, social behavior, motivations and goals. The user interacts with this world through some presentation. This presentation may be an objective, third person perspective on the world, or it may introduce various kinds of dramatic filtering − effecting camera angles and point of view in graphical worlds, or changing the style of language used in textual worlds.The drama manager can see everything happening in the world. It tries to guide the experience of the user in order to make a story happen. This may involve changing the physical world model, inducing characters to pursue a course of action, adding or deleting characters, etc. Structure of the reportThe rest of the report is divided into two main sections, Believable Agents (character) and Interactive Story, and a small section describing interactive video work. In the believable agents section, I will first describe the Oz research philosophy. Then I will present work related to believable agents (artificial life, virtual humanoids, embodied characters, chatterbots, and behavioral animation) in light of this philosophy. Finally, I will discuss why believable agents is an important and interesting research area. In the interactive drama section, I will first define the problem of interactive drama in terms of the inherent tension between the concepts of interaction and drama. After a brief description of the Oz drama manager, I will describe three design dimensions which help structure the design space of interactive drama systems. In the small section, I’ll describe the relationship between the virtual world approach to story and character vs. the interactive video