Trading in a multiplayer board game: Towards an analysis of non-cooperative dialogue

Trading in a multiplayer board game: Towards an analysis of non-cooperative dialogue Markus Guhe (m.guhe@ed.ac.uk) , Alex Lascarides (alex@inf.ed.a.uk) School of Informatics, Informatics Forum, 10 Crichton St, Edinburgh EH1 2HX, Scotland Abstract We collected and analysed a small dialogue corpus of people playing The Settlers of Catan. Dialogues are trading negotia- tions where Gricean maxims of cooperativity often break down as players adopt conflicting intentions in their attempt to win the game. This has consequences for what information players are sharing and for the sincerity of their contributions. In this paper, we motivate and describe a two-level scheme for analysing non-cooperative dialogues, where both levels are in- terdependent. Each dialogue move is a move in the game (e.g., an offer to trade), and a coherent contribution to the dialogue so far, connected to a prior segment with a coherence relation, such as indirect answerhood or rejection. Parsing and gen- erating coherence relations is computationally feasible (e.g., Baldridge & Lascarides, 2005), and here we’ll argue that their semantics help to identify the game move, even when it is im- plicated rather than linguistically explicit. Keywords: non-cooperative dialogue; dialogue move; negoti- ation; The Settlers of Catan; JSettlers; multiplayer game. Non-cooperative dialogue Standard accounts of dialogue usually assume that the agents cooperate with one another on at least two levels (Grice, 1975): they coordinate the conventions that govern linguis- tic meaning (basic cooperativity); and they share attitudes to- wards what is said, including shared intentions (content co- operativity). Tutoring is a widely investigated example where content cooperativity is a reasonable assumption. But there are many dialogue scenarios where conflicting preferences compel agents to perform dialogue moves that aren’t content cooperative. Such situations range from differ- ences in preferences with relatively low stakes (e.g., whether to go to a French or an Italian restaurant) to very high, life changing, stakes (e.g., a cross examination of a defendant by a prosecutor in court). Lying in court has potential high re- wards (if the lie is not uncovered) as well as high penalties (if it is). But telling the truth or lying are just the two extremes in a spectrum of non-cooperative behaviour. To illustrate this, consider the following cross-examination of a defendant by a prosecutor (from Solan & Tiersma, 2005): (a) Prosecutor: Do you have any bank accounts in Swiss banks, Mr. Bronston? (b) Bronston: No, sir. (c) Prosecutor: Have you ever? (d) Bronston: The company had an account there for about six months, in Zurich. The locutionary content of both (b) and (d) are true, but Bronston succeeds in deflecting the prosecutor’s enquiry with a misleading implicature with (d): (d) implicates that Bron- ston never had any Swiss bank account, and this is false. In this paper, we describe dialogue moves in non- cooperative situations, drawing on data from a dialogue cor- pus of people playing The Settlers of Catan. In the corpus, each dialogue move is aligned with a machine readable ver- sion of the game state. We present a scheme of the types of dialogue moves that occur in our corpus. Our eventual goal is to build a dialogue system that plays The Settlers of Catan, engaging in non-cooperative dialogues like humans do. For such a system, the agent playing the game will use the dia- logue moves from that scheme to interact with the other play- ers so as to forward its chosen game moves. This will require us to parse and generate the semantic content of these dia- logue moves; we will exploit coherence relations from SDRT for this purpose (Asher & Lascarides, 2003). The Settlers of Catan The Settlers of Catan is a multiplayer board game set on the fictional island Catan. Catan is represented by a map con- sisting of hexes (see Fig. 1; see catan.com for the full set of rules). Two to four players settle on the island by building set- tlements and cities connected by roads. It is a zero-sum game: the first player to win 10 victory points wins and all others lose. One obtains victory points by, for example, building a settlement (1 point) or a city (2 points). To build, one needs resources: clay, wood, rock, ore and sheep. Players take turns and attempt to obtain resources and to build. A turn starts with the roll of dice. Each player poten- tially obtains or loses resources through dice rolls. This de- pends on a combination of: the number rolled, the location of game pieces on the board, and the resources currently held. (So, future game states are non-deterministic, necessitating players to calculate the risks of moves). The player whose turn it is can trade resources with the bank or other players and can use resources to build roads, settlements or cities. Dialogues where the players trade resources surface dur- ing game play as the players try to exchange resources with one another. Their decisions about what resources they want and what they are prepared to give up are influenced by what they need to build, e.g. a road requires 1 clay and 1 wood. A player can only build on a location if it touches one of his already existing pieces (road, settlement or city); all settle- ments and cities must be separated by at least 2 roads (of any player). Thus, players’ decisions about trades are not only de- termined by the decisions about what they want to build and where they want to build it, but also by their estimates of what will most advance, or undermine, the building strategies of the other players (see Thomas, 2003). Players can agree any trade; they can even lie or bluff, as found in classic concep- tions of bargaining games (Osborne & Rubinstein, 1990).