Adialogue tree, orconversation tree, is a gameplay mechanic that is used throughout manyadventure games[1] (includingaction-adventure games[2]) androle-playing video games.[3] When interacting with anon-player character, the player is given a choice of what to say and makes subsequent choices until the conversation ends.[3] Certainvideo game genres, such asvisual novels anddating sims, revolve almost entirely around these character interactions andbranching dialogues.[4]
The concept of the dialogue tree has existed long before the advent ofvideo games. The earliest known dialogue tree is described in "The Garden of Forking Paths", a 1941 short story byJorge Luis Borges, in which the combination book of Ts'ui Pên allows all major outcomes from an event branch into their own chapters. Much like the game counterparts this story reconvenes as it progresses (as possible outcomes would approach nm where n is the number of options at each fork and m is the depth of the tree).
The first computerdialogue system was featured inELIZA, a primitivenatural language processingcomputer program written byJoseph Weizenbaum between 1964 and 1966. The program emulated interaction between the user and anartificial therapist. With the advent ofvideo games,interactive entertainment have attempted to incorporate meaningful interactions with virtual characters.Branching dialogues have since become a common feature in visual novels,dating sims,adventure games, androle-playing video games.[4]
The player typically enters the gameplay mode by choosing to speak with anon-player character (or when a non-player character chooses to speak to them), and then choosing a line of pre-written dialog from a menu. Upon choosing what to say, the non-player character responds to the player, and the player is given another choice of what to say. This cycle continues until the conversation ends. The conversation may end when the player selects a farewell message, the non-player character has nothing more to add and ends the conversation, or when the player makes a bad choice (perhaps angering the non-player to leave the conversation).
Games often offer options to ask non-players to reiterate information about a topic, allowing players to replay parts of the conversation that they did not pay close enough attention to the first time.[3] These conversations are said to be designed as atree structure, with players deciding between each branch of dialog to pursue. Unlike a branching story, players may return to earlier parts of a conversation tree and repeat them. Each branch point (or node) is essentially a different menu of choices, and each choice that the player makes triggers a response from the non-player character followed by a new menu of choices.
In some genres such asrole-playing video games, external factors such as charisma may influence the response of the non-player character or unlock options that would not be available to other characters.[3] These conversations can have far-reaching consequences, such as deciding to disclose a valuable secret that has been entrusted to the player.[3] However, these are usually not realtree data structure in programmers sense, because they contain cycles as can be seen on illustration on this page.
Certain game genres revolve almost entirely around character interactions, includingvisual novels such asAce Attorney anddating sims such asTokimeki Memorial, usually featuring complex branching dialogues and often presenting the player's possible responses word-for-word as theplayer character would say them. Games revolving around relationship-building, including visual novels, dating sims such asTokimeki Memorial, and some role-playing games such asShin Megami Tensei: Persona, often give choices that have a different number of associated "mood points" which influence a player character's relationship and future conversations with a non-player character. These games often feature aday-night cycle with a time scheduling system that provides context and relevance to character interactions, allowing players to choose when and if to interact with certain characters, which in turn influences their responses during later conversations.[4] Some games use areal-time conversation system, giving the player only a few seconds to respond to a non-player character, such asSega'sSakura Wars andAlpha Protocol.[5]
Another variation of branching dialogues can be seen in theadventure gameCulpa Innata, where the player chooses a tactic at the beginning of a conversation, such as using either a formal, casual or accusatory manner, that affects the tone of the conversation and the information gleaned from the interviewee.[4]
This mechanism allows game designers to provide interactive conversations with nonplayer characters without having to tackle the challenges ofnatural language processing in the field ofartificial intelligence.[3] In games such asMonkey Island, these conversations can help demonstrate the personality of certain characters.[3]