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Defining Dialogue Systems
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Defining Dialogue Systems

July 8, 2008 Article Start Previous Page 3 of 5 Next

Hub-and-Spokes Dialogue

Though ultimately a variation of the previous method, Hub-and-Spokes Dialogue creates a very different conversation flow compared to basic Branching Dialogue. The player listens to the NPC's lines and then chooses their response from the main "hub" of the conversation.

After hearing the NPC's response, the player either returns to the main hub, from which they can ask the same question again or inquire about another topic, or enters a deeper hub with more options to choose from.

The player can typically always find their way back to any hub by navigating through their responses, and thus can explore the dialogue in any order they wish. In this manner, a player can exhaust a conversation by trying every possible option at their disposal (with no penalty), and the interaction only ends when the player chooses the "goodbye" option.

Most conversations in Mass Effect and other BioWare titles take this form, with occasional basic Branching Dialogue implemented when the player has to make an important decision that may affect quest outcomes or the NPC's disposition towards the player.

Hub-and-Spokes Dialogue gives the player more freedom and control over conversation and often allows them to interrogate NPCs to find out every last piece of information about them. However, this method of dialogue tends to create conversations strongly divorced from reality.

The NPC usually has infinite patience for the player's strange inquisitions, and every dialogue plays out like an interrogation as the player keeps pressing the NPC for info. Furthermore, the player hears a lot of the same lines over and over as he navigates between hubs, potentially breaking immersion.

Parser-Driven Dialogues

While the original conversation simulator, ELIZA, used a text parser to get player input, this method is relatively rare today. Some experimental titles like Façade, however, still explore its possibilities.

In a parser-driven dialogue, players type their exact response and the system attempts to parse the input in a way it can understand. The NPC then replies with one of a number of pre-set responses, or builds a response based around the words used by the player in combination with pre-set phrases. In many cases, the player directly controls the flow of conversation, veering wildly off-topic whenever they wish without eliciting much surprise from the NPC.

Façade's design, however, always attempts to keep the player on track. In this game, the player plays an active part in dealing with marital troubles as a third-party helping a couple work through their problems.

Although input from the player comes from a text parser, Façade tries to keep conversations as natural as possible by choosing a response based on not only the player's immediate input, but also their behavior thus far and the current state of the dialogue.

Procedural Arts' Façade

In Façade, the conversation always moves forward, despite the player's best attempts to change subjects, as the NPCs always try to return to the subject at hand. The conversation can go many different ways, and a message after the game ends encourages the player to replay the game many times.

Parser-Driven Dialogues are rare in modern games for two reasons. The first is that the freedom they provide is extremely time-consuming to produce. The system needs hundreds of potential responses to accurately simulate a single, short conversation.

The second reason is that even the most robust parsers frequently misinterpret the player's input. In Façade, an innocent inquiry can send the NPCs into shock, horrified by what they thought the player just said. These misunderstandings ruin virtual relationships and frustrate the player, while at the same time exposing the program's failings and distracting the user from the interaction.

Article Start Previous Page 3 of 5 Next

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