LECTURE 3: BDI LOGICS

Transcription

1 are mutually exclusive LECTURE 3: BDI LOGICS Marc Pauly & Mike Wooldridge University of Liverool, UK What is intention? Two sorts: resent directed attitude to an action function causally in roducing behaviour future directed attitude to a roosition serve to coordinate future activity We are here concerned with future directed intentions 2 1 The Logic of Intention We have one asect of an agent, but knowledgebelief alone does not comletely characterise an agents We need a set of connectives, for talking about an agent s ro-attitudes as well Agent needs to achieve a rational balance between its attitudes: should not be over-committed; should not be under-committed Here, we review one attemt to roduce a coherent account of how the comonents of an agent s cognitive state hold together: the theory of intention develoed by Cohen & Levesque Here we mean intention as in It is my intention to reare my slides 1 Desiderata for Intention Cohen-Levesque identify seven roerties that must be satisfied by intention: 1 Intentions ose roblems for agents, who need to determine ways of achieving them If I have an intention to, you would exect me to devote resources to deciding how to bring about 2 Intentions rovide a filter for adoting other intentions, which must not conflict If I have an intention to, you would exect me to adot an intention such that and 3

2 was not ossible also Intentions are not closed under imlication) 6 action action i believes i has goal of haens next has just haened Cohen-Levesque use a multi-modal logic with the following major constructs: The Language 4 It would not be rational of me to adot an intention to believed if I Agents do not believe they will not bring about their intentions Agents believe their intentions are ossible That is, they believe there is at least some way that the intentions could be brought about being equal, it will try an alternative lan to achieve Agents track the success of their intentions, and are inclined to try again if their attemts fail If an agent s first attemt to achieve fails, then all other things 7 belief accessibility relation B for every agenttime air, gives a set of belief accessible worlds; Euclidean, serial, transitive gives belief logic KD4 goal accessibility relation G for every agenttime air, gives a set of goal accessible worlds Serial gives goal logic KD Each agent allocated: Semantics are Krikeossible worlds: each world is infinitely long linear sequence of states The Semantics This last roblem is known as the dentist roblem I may believe that going to the dentist involves ain, and I may also intend to go to the dentist but this does not imly that I intend to suffer ain! and I intend that If I believe, I do not necessarily intend 7 Agents need not intend all the exected side effects of their intentions it as an intention It would not normally be rational of me to believe that I would bring my intentions about; intentions can fail Moreover, it does not make sense that if I believe is inevitable that I would adot 6 Under certain circumstances, agents believe they will bring about their intentions

3 test action B, and then done * * * * * * ) - 10 the agent believes the goal has been satisfied; the agent believes the goal will never be satisfied Before it dros the goal, one of the following conditions must hold: It has a goal that eventually becomes true, and believes that is not currently true, an agent has a ersistent goal of if: &!,! '! Persistent Goals agents do not indefinitely defer working on goals agents do not ersist with goals forever; C&L intend this assumtion to cature following roerties: Another constraint: A realism roerty agents accet the inevitable Gives the following inter-modal validity: A constraint: G 11 Adatation of definition allows for relativised intentions Examle: I have an intention to reare slides for the tutorial, relative to the belief that I will be aid for tutorial If I ever come to believe that I will not be aid, the intention evaorates Main oint: avoids ever commitment C&L discuss how this definition satisfies desiderata for intention So, an agent has an intention to do if: it has a ersistent goal to have believed it was about to do 2 ' 0 x 3 1x Intention to Act 9 A temoral recedence oerator, &! q! strict sometime oerator, #x x!: Also add some oerators of temoral logic, always), and sometime) can be defined as abbreviations, along with a followed by Add in some dynamic logic) oerators for describing the structure of event sequences Actions & Time

4 76 * * * * * * ) q - e < x e = q 14 9 y : n 4 n x y And the related concet of mutual belief 4 n x y y n times x n times 76 First, define alternating belief 12 does not cature and adequate notion of cometence ; does not adequately reresent intentions to do comosite actions; requires that agents know what they are about to do fully elaborated intentions; disallows multile intentions Critique of C&L theory of intention Singh, 1992): 1 reresents ultimate goal that agent is aiming for by doing e; roosition q reresents what it takes to at least make an honest effort to achieve Here: An attemt is a comlex action that agents erform when they do something e) desiring to bring about some effect ) but with intent to roduce at least some result q) In English: 0 1x e x e ; 4 An attemt is a comlex action: 13 We will look at request C&L use their dynamic logic-style formalism for reresenting these actions Key observation: illocutionary acts are comlex event tyes cf actions) C&L used their theory of intention to develo a theory of several seech acts 2 Semantics for Seech Acts

5 * * ) - * * ) > skr e < 1 A request is an attemt on the art of skr, by doing e, to bring about a state where, ideally, 1) addr intends, relative to the skr still having that goal, and addr still being helfully inclined to skr), and 2) addr actually eventually does, or at least brings about a state where addr believes it is mutually believed that it wants the ideal situation Requests Defined in English In English: 16 [C]onsider an agent [x] to be helful to another agent [y] if, for any action [e] he adots the other agent s goal that he eventually do that action, whenever such a goal would not conflict with his own In English: :e & y x e x e x e > y Definition of helfulness needed: 19 [A] seaker is viewed as having erformed a request if he executes any sequence of actions that roduces the needed effects By this definition, there is no rimitive request act: 17 9 addr skr skr and & 0 addr 1addr skr addr > addr skr where ;? = skr addr e ; 4 = Requests Defined