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Defining Dialogue Systems

July 8, 2008 Article Start Page 1 of 5 Next

[In an in-depth Gamasutra analysis piece, Ellison looks at the universe and history of player-NPC dialogue interaction in games, analyzing titles from Mass Effect through Facade to The Sims and beyond.]

In 1966, Joseph Weizenbaum created ELIZA (pictured below), a computer program designed to emulate interaction between the user and an artificial therapist. Ever since, designers of interactive entertainment have attempted to incorporate meaningful interactions with virtual characters in order to aid immersion.

The most popular Western RPGs, like the Baldur's Gate and Fallout series, live and die by the strength of their dialogue and the player's ability to influence the non-player characters. Japanese romance games such as Konami's Tokimeki Memorial and visual novels like the Phoenix Wright series revolve almost entirely around character interactions.

Even action titles like Grand Theft Auto: San Andreas incorporate elements of non-violent character interaction to make the world come to life. However, while a great deal has been written about the process of creating game characters and writing for games, very little literature has addressed the mechanics behind character interaction in games.

While likeable design and well-written dialogue are among the most vital aspects in engaging a player with in-game characters, the systems of interaction certainly play an important role as well.

NPC interaction gameplay is a part of nearly every modern game, in the form of dialogue, barking orders at followers, or just choosing who to talk to in town. However, the western games industry has always found it difficult to create successful games based solely around character interactions, even though such things are popular in other media (television, novels, etc.).

The difficulties in interactive conversation lie in giving the player the illusion of freedom while still feeling natural and driving the story forward along interesting paths. Finding the most interesting and engaging way for a player to interact with game characters and develop relationships potentially opens up a wide array of game concepts and themes not typically explored by western game developers.

NPC interaction gameplay has seen numerous permutations throughout the years, but most can be separated into a few categories based on common design patterns. Gameplay varies with regard to level of interactivity, interface, and how the game presents the player with his potential responses. What follows is an overview of the gameplay of character interaction to date.

Non-Branching Dialogue

In games using non-branching dialogue, the simplest form of interaction, the player walks up to an NPC and initiates conversation. The NPC delivers his or her lines and the conversation ends. Alternately, initiating a conversation with an NPC triggers a cutscene where the player's avatar and the NPC have a non-interactive dialogue.

If the player talks to the same NPC again after certain events, the NPC may have different things to say, but the player never has any control over the conversation. The only decision-making involved is whether or not to talk to the NPC.

This type of interaction is extremely common and easy to implement, and can therefore be seen in almost any game featuring non-hostile NPCs, such as the original Final Fantasy and The Legend of Zelda: Ocarina of Time. While non-branching dialogue is still a regular facet of modern games, due to the absence of gameplay it is included in this article only for reference.

Branching Dialogue

Game dialogue becomes more interactive when conversations can take different paths. The player reads dialogue and chooses their response from a limited set of choices available to them. Conversation typically moves forward such that the player cannot go back to previous topics or responses.

From this basic framework, NPC interaction can be as simple as the player answering a yes or no question in a three-line conversation with a random NPC in town, or as complex as the relationship-building simulations in Japanese dating games like Tokimeki Memorial.

In games where branching dialogue is the primary gameplay focus, the player's choices often affect the NPCs' attitudes toward the player one way or another, with the player attempting to guess the "best" response in order to maximize NPC disposition.

One common technique employed to give the player a greater illusion of freedom is to have multiple responses lead to the same path. This is usually done as an attempt to limit the quantity of dialogue that must be produced for the game. Therefore, branching dialogue usually curves back in on itself such that while an individual choice may immediately produce a unique response, the rest of the conversation is typically not unique to that choice.

In games where the goal of conversation is to improve the player's relationship with the NPC, however, while every choice may not change the course of the dialogue, each choice may have a different number of "mood points" associated with it, and thus the player must still carefully consider his options at every turn.

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Game Designer


Tynan Sylvester
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I spent several fulltime months creating a game with a unique 'dialogue' system you might be interested in. It's actually an earnest attempt to make a dynamic tactical game about picking up chicks in bars.

I had to abstract out the actual words and focus on emotions. The main problem with this system is that it doesn't read well because it is so abstract.

The game is called The Player League. You play as a guy in an underground league of bar players.

Here's the download and links to my design articles about it:

Fernando Angelico
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Thanks , im gonna read those articles.

Thanks tynan

Lorenzo Wang
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This article reminds me of a really interesting Turing test that noted cognitive academic Douglas Hofstadter as involved in:

(skip down to Post Scriptum)

I think the true Turing test will be the day a computer can pass one. In that sense, I would love to see how AI would play Facade.

Mike Rozak
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I've been playing with NPC dialogues for awhile and discovered the following:

1) There's no "grand unified theory"; humans (and hence NPCs) are too complex. The author really needs a toolkit of branching narratives, queries, and more free-form NPC responses (maleable branching narratives). Players need a menu of the most common options, but the ability to type (or speak) a more complex query, such as: "Where does CHARACTER live?"

2) The designer needs to always ask him/herself, "Why am I giving this choice to the player?" See .

My in-progress game, that uses a lot of dialogue, is at .

Stephen Dinehart
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This is a nice exploration, most of the terms you are looking for have already been established in narratology. As much as I like to make up terms it's helpful to use standard terms sometimes. Interactive dialog is still in its infancy. Bioware is without question the leader in interactive RPG dialog system design, but due to the fact that they rest on established conventions borrowed from times past. Like the rest of us they seem to be caught in a iterative design process, making small steps in innovation.

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The article certainly did an adequate job describing the different types of dialogue systems out their pros and cons, but I would have liked to have seen a bit more insight into what kinds of games the author feels these systems are best suited to, what the future is of some of the more fledgling models (and even the established ones as well), etc.

Personally, I think Mass Effect represents the best implementation of an RPG dialogue system. It allows the player to get as much information as they want from any given NPC, and provides many unique paths during critical moments based upon the player's attitude. It's certainly not without its faults, however. Limiting the options to a sort of three-tiered Nice/Ambivalent/Jackass model gives just about any player an option they would have chosen themselves (albeit more eloquently put for most people I'd wager). There's a lot of overlap between the options, however, leading to a lot of false decision making. Limiting information concerning what the player's avatar will actually say to a two to three word summary also creates problems, as the player will soon discover that their avatar will often say something they hadn't intended them to say.

Jens Andersson
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I'm also hugely interested in this area and some time ago I did an prototype of a dialogue-system that tries to do things differently. It turned out pretty well, so feel free to check it out at

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Re: Anon

I think dialogue systems have gone as far as they can go, at least as far as basic mechanics go. At this point, any given dialogue is as open or as closed as the designer wants it to be - a general, ambiguous response can allow as much interpretation as many very specific responses. However, supplementary systems, overall presentation, as well as more responsiveness can add greater weight to a conversation in much the same way as the myriad of subsystems have made combat a very complex thing (but without really changing how things actually work). Purely a thought and not necessarily a practical system, but tracking what movements a player does before picking a response could allow a designer to pick out additional 'flavors' of any given response (ie a player that flips back and forth between choices before picking could be understood as verbally hesitant while someone who does nothing before picking as thoughtful and introspective while someone that picks a choice but then waits as cautiously spoken) or a system that reads a player's button presses and responses to that (a player tapping a button continually is impatient, a player that presses a button hard is giving more 'oomph' to the statement they select). Making conversations more than talking heads (even Mass Effect does this) can give conversations more of a realistic feel even if they aren't realistic themselves - allowing players or showing players their character's moving while talking (walking down a hall or merely waving their hands and doing something other than ignoring the game world while taking) would give more immersion to dialogue. As conversation (and personality) are very intangible and even two very different people can say the same thing, blending dialogue and action (and character action) can give more weigh which I think is the real current limitation. In the real world, how often do you talk as you do in RPGs - that is, stopping everything you are doing, facing each other, and talking without any other action. Probably very little - more likely, you are talking within context of another action.

John Mawhorter
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You mention non-branching dialogue only briefly when it is one of the most used mechanics for dialogue in certain genres. While I get that your focus is on gameplay and dynamic dialog systems, a non-branching dialogue can also have a gameplay element. Choosing who to talk to, when to talk to them, and at what time is a factor in many games, even those with branching dialogue that let you make choices in conversation. In this context I feel you shouldn't ignore non-branching dialogue as non-interactive. The interaction is starting the dialogue.

Mark Zartler
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Excellent article.

I've always been curious as to what Machine Learning could accomplish here. Is there a ML community at work in games? Dialoging and user driven actions seem ripe for this, but then again, it may be another application where there never enough data.

Anyone using statistical methods?

Mark Zartler