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Interactive drama page

An interactive drama takes place within a virtual world in which the user has a high degree of freedom to physically and mentally interact with non-player characters and objects within a dramatically interesting experience which is different on every play, and adapts to the user's interactions.

A linear or multi-linear story is clearly not an interactive drama, because it cannot satisfy the need for interaction which has a clear effect on the drama development a sufficently large number of times (the number of fundamentally different narratives which can be generated is very limited). There are games with no explicit story structure (simulations) in which the user is encouraged to perceive their own stories within the world. These stories are truly interactive, but lack the structured drama development required to ascertain satisfaction of the need for a dramatically interesting experience. This tends also to lead to a lack of ability to emphathise with characters, an ability which may increase immersion.

Motivation

Storytelling is appreciated by many people, as both teller and audience. In the past stories were only told orally, with audience participation. It is still true that listening to a friend narrating a story is an enjoyable way to spend time. However, as storytelling has evolved –- through drama, writing, print, film and television –- interactivity has been neglected. Receivers (listeners, readers or viewers) of a story will often want to become more involved in the storyworld, perhaps even to become a character. An interactive drama offers a world in which the participant can have a real effect -– both long and short term –- on the drama which they are experiencing.

Many computer games involve a story, which in most cases is an essentially linear story or series of stories (multi-linear). The most complete stories can typically be found in Role-Playing Games (RPGs), First-Person Shooters (FPSs) and Adventure Games (AGs). This linear element constrains game development because it limits the user to following one of the pre-defined story-lines. However, the incorporation of a story enriches the game, by providing a cause and a motive for the game and the user's actions, thus greatly increasing the potential for immersion and engagement.

Drama when used in this article refers to "moment by moment action, a scenic rendering of speech and behaviour of characters, careful detailing of specific events, commonly contrasted by panorama" .

Virtual worlds

The exact depiction of the world will depend on the genre of story to be experienced. For example a {\it Dungeons and Dragons} RPG needs to include dungeons and monsters. The world in which the drama will take place needs to have an appearance of completeness which is sufficently high to allow the users to feel that they are experiencing freedom within the virtual world.

There are many existing virtual worlds in which an interactive drama could take place. These include game worlds, such as Fallout 3 \cite{fallout} and Neverwinter Nights \cite{nwn}; and virtual realities, such as Second Life \cite{sl} -- in which the user creates their own avatar and is considered to be a resident of the world. The use of an open source 3D environment for an interactive drama would give the programmer greater overall control, but may not be compatible with other virtual worlds.

Interaction with objects

The user of an interactive drama is likely to become frustrated if they do not perceive themselves to be able to freely select their actions within the virtual world, within reasonable limitations. At a minimum this freedom should be adequate for user-friendly interaction with characters, objects and scenes of the drama. As Laurel \cite{laurel} explains, it ``is difficult to imagine life, even a fantasy life, in the absence of any constraints at all, for example gravity within a game world is not seen as limiting a user's freedom. Providing that any constraints are consistent with the user's perception of the game world the user will still believe that they are free within that world.

This can include interaction with other characters as if they were objects. This is a representation of actual physical interactions in the `real' world. There is not a clearly defined boundary between this requirement and the next, that of social interaction. Many actions may combine both, for example assaulting another character involves interacting with them as an object, but also has a strong underlying social component.

Social interaction

Social interaction involves interaction with other characters within the virtual world on a social level. For example gestures, spoken and emotional communication and expressions are all forms of social interaction. These should all be available to characters within the virtual world. Each character should be able to interact with all of the other characters in each of these ways. The use of language communication is discussed further in this section, as this is the most frequently researched of the social interactions.

The user will ideally be able to communicate freely within the virtual world, and be understood. This is frequently interpreted as requiring natural language processing (NLP), as for example in Facade \cite{facade}. This relies on the assumption that NLP provides the highest level of freedom and interactivity. However, this is not necessarily true. Current NLP technology will not allow characters to fully understand natural language, which means that only a restricted set of sentences will have the expected interpretation and thus the user must either know, or guess, the required input for their desired action.

A method which presents the user with a clear set of possible options may be considered to be more user friendly. These options must cover a wide range, to allow the user to identify a suitable representation of their desired action, otherwise it will be seen as limiting the user's freedom. An additional advantage of this method is that the user will be presented with options which they may not otherwise have considered, and thus supplements their imagination. This means that the user is still free to act but is not relying solely on their own creativity. In addition this method increases the level of mutual understanding between characters.

Within the drama other characters will mentally interact with one another. They should also initiate interaction with the user. This is as would be expected in a natural unfolding of a drama, whether interactive or otherwise.

Fundamental difference

Each time the user participates in an interactive drama they should identify the story which they experience as being an essentially a new story. To achieve this the main storyline will need to significantly differ every time the user participates, which requires changes in the background and the inciting incident. Insignificant changes, such as only the ending differing, or characters having a different trivial conversation, will not be sufficient. The unfolding story should vary each time the user participates, in such a way that the user would identify it as essentially a new story each time. The difference in the story needs to be apparent from the outset of the drama.

For example, in a murder mystery the uniqueness of the drama occurs in the set-up, the characters, murder and scenes. This means that two mysteries with the same set of characters, but with a different character being the victim, will be essentially different stories, as this will cause a fundamental change to the actions of the characters, the identity of the murderer, and the clues required to discover the murderer and their motive. A change to the set of characters, or the scene, will also lead to a fundamentally different story. However if the set of characters, the scene and the murder remain constant, with the only difference occuring in the identity of the murderer, then the stories cannot be considered to fundamentally differ. As there will only have been subtle difference in the drama which determines that character's identity as the murderer rather than another.

The variation in the story must be highly responsive to the user's interactions. The user is essentially finding a narrative path through the storyworld in which an unnoticed dramatic interest guide will be the computerised playwright. The user should be able to act as and when they desire in ways which will have a perceivable long and short term effect on the narrative.

Dramatic structure

For the interactive drama to be successful the experience must be dramatically interesting for the user. The use of a dramatic structure supports the dramatic interest of the experience. Through history, storytelling and drama have captured the interests of many theorists. This began with Aristotle \cite{aristotle} in ancient Greece, and has continued with modern theorists including: Barthes \cite{bar74}, Esslin \cite{ess78}, Propp \cite{propp}, and Todorov \cite{tod77}.

As a result of this research there are structures which can be used to aid in the development of an interesting drama. Freytag \cite{freytag} proposed a graphical form for the analysis of plots, which is known as Freytag's Pyramid, as shown in figure \ref{freytagstructure}. This referred to as a `dramatic arc' \cite{laurel} in this paper. The dramatic arc outlines the basic rise and fall typically found in an interesting drama. This begins with an inciting incident, which provides the mood and motive for the drama ({\it a}). The suspense will then be expected to steadily climb due to the increase in complications in the unfolding plot ({\it b}). This will cease at the `climax' point ({\it c}). Following this the dramatic arc steadily descends ({\it d}) as the complications are resolved, and the drama reaches closure ({\it e}).

• Freytag's plot structure (as given in \cite{freytag})
  Freytag's plot structure (as given in \cite{freytag})

It is possible for an interesting drama to occur without a dramatic arc being followed, for example there may be a lack of closure. However, the more closely a drama conforms to the dramatic arc the more difficult it becomes to claim that it is not dramatically interesting.

Dramatic arcs have been utilised in previous interactive drama research. For example the Oz Project and IDtension require generated narratives to follow a dramatic arc \cite{oz, idtension}. Fa\c{c}ade uses a structure which they call neo-Aristotelian, an adaptation of the Aristotelian structure to interactivity \cite{aristotle}.

Propp's morphology of the Russian folktale \cite{propp} provides a structure for Russian folktales, in the Aarne index \cite{Aarne}, using a specific set of functions and characters. Propp's functions have been exploited by many systems, such as OPIATE \cite{fc}. With the exception of \cite{dpge} very little attempt has been made to extract the morphology of a different set of tales, or story genre, to aid in the unfolding of interactive drama.

Although not all interesting dramas conform to a specific morphology, it is more likely that a drama which does conform to a well known dramatically interesting strcture will be of interest to a wide audience. For example the Field's \cite{syd-field2} morpohology has helped to provide the structure of Hollywood films for many years, and is still one of the most used script structures in that domain.

Esslin \cite{ess78} explains that any drama needs to capture and maintain the involvement of the audience by being constantly interesting. The audience are likely to frequently lose interest in the main storyline. It is thus essential to have sub-stories within the overall story, as these will ensure the continued attention of the audience. Such sub-stories will add to the complication of the plot, thus increasing the overall suspense within the drama. The events within these sub-stories must also follow a clear structure, as this will ensure the continued engagement of the audience. Sub-stories may be nested.

For example there may be a science fiction in which the main plot involves rescuing a spaceship and its crew, who are stranded in deep space. Possible sub-stories which could occur within this drama include: two crew members falling in love; or the captain's quest for a novel solution to reduce the energy consumption of the spaceship. The structure of the second sub-story could involve the engineer proposing a new way of conserving energy (the inciting event), a discussion of this method (the rise), the captain's decision as to whether to follow this proposal (the climax), and possibly the reasoning behind this decision (the closure).

Plot graph structure

A plot graph structure can be used to generate an interactive narrative. In this there are certain stages of interaction. These vary in length depending on the specifications of the system, but can be whole scenes or only a few seconds of action. Following these stages there will be pre-defined actions or sequences of actions which will lead to a new stage of interaction. Different actions (by the user or other characters) will cause variance in the narrative, as they may result in a different stage of interaction being the next to occur.

The major shortcoming of all systems which use a plot graph structure is their lack of extendability and generality. This means that there is also a lack of replayability. Each possibility for the narrative must be pre-defined, in itself and in the context of the stages of interaction which can precede or follow it. This involves a large amount of pre-definition. There will also only be a limited number of possible paths through the storyworld, as the plot graph must be followed. Repetition will occur after only a few experiences with the system, and thus the requirement of a fundamentally different narrative cannot be realistically satisfied -- as such a large volume of material will need to be pre-defined.

A plot graph structure is used by interactive drama systems such as: references.

Other techniques

Other techniques for interactive drama creation include the use of Proppian structures, dilemmas, and schemas as a basis for dramatic interest.

Character autonomy

Many interactive drama groups involve autonomous characters in their work. This may lead to emergent drama.

Terminology

There are various terms used for the research field, for example `interactive drama', interactive storytelling and `interactive narrative'. The term used by each research group tends to reflect their short-term presentation technique, for example `interactive narrative' is often used for systems which currently generate a high-level plot outline. These systems can be discussed within the same evaluation as their core aims are the same. The term `interactive drama' is used here as this was the term which was first used, and thus is the most reflective of the extensive coverage of systems by this paper, which incorporates systems which have been developed throughout the course of research in this field. As discussed in section \ref{definition}, drama is also the most appropriate term for the ultimate aims of research in this field.

Related work

Other usages of interactive drama include that by the BBC when you can text what you want to happen at branch points. This is not the same concept. In an interactive drama the user takes the role of a character and is able to completely control the actions of that character, which will affect the virtual world and the story which they experience.

There are also research groups which have created systems in which the user can affect the story but does not take first-person control of a character.

Also of some relevance is story understanding and story generation systems.