Influencing A Strategy for Goal Adoption in BDI Agents

Influencing : A Strategy for Goal Adoption in BDI AgentsHrushikesha Mohanty1, Manas Ranjan Patra1, K Sagar Naik21 AI Lab., Dept. of Computer and Information Sc., University of Hyderabad,Hyderabad 500 046, India, hmcs@uohyd.ernet.in2 Network Lab., University of Aizu, Tsuruga, Aizu-Wakamatsu City,Fukushima, 965 Japan, k-naik@u-aizu.ac.jpAbstractIn recent years, computing systems based on Belief-Desire-Intention (BDI) paradigm have received considerable attention in the area of Agent Technology. This paradigm has been proposed to model human cognitive behaviour in terms of three cognitive states viz., belief, desire, and intention. It is believed that one’s goal-adoption behavior largely depends on its cognitive states. Hence, an agent (influencing agent) can influence another agent (target agent) by acting on latter’s cognitive state to make it adopt a goal of former’s interest. On giving a formal definition to agent cognitive states we present a framework for influencing that achieves goal adoption at target agent. Also the uses of communication tones and social norms in a process of influencing are shown. We explain the use of the proposed framework in a production management scenario.Key words : BDI agent, Cognitive states, Influencing, Social Laws1. IntroductionC urrently, there has been a growing interest in developing interoperable software agents which combine cognitive abilities to facilitate understanding of complex real situations, and thereby behave appropriately [9,10,21]. The related issues which are under active research are : co-operation[2,13,29,31], negotiation[16,17,33], c ollaboration [12, 14, 18, 19], planning [8, 11,22], and co-ordination [30]. Of late, another issue which has been studied in connection with agent-interactions is influencing [5]. The purpose of influencing is to make an agent adopt or abandon a goal. In [5], influencing has been achieved by use of strategies(operators) like promise of prize, threat of sanction and search for cooperation. Later in [7], influencing has also been studied from a different perspective which is achieved by operating on evolved information like agent dependencies. There it is said that an agent’s dependence on another is predictive of one’s goal of influencing the other, as well as of the latter’s power of influencing the former.Unlike the above approaches, here we propose that influencing is a process that operates on primitive internal composition of an agent. Towards this end, several proposals on internal composition of agents have been made [6,15,23,25,27]. Among those the Belief-Desire-Intention (BDI) paradigm [14,24] has received considerable attention in which three mental attitudes viz., belief, desire, intention have been used to model human cognitive behaviour. We adopt the BDI agent model and based on that analyze the process of influencing. BDI agents do not adopt goal arbitrarily, rather adoption of goal is based on one’s beliefs. An agent strives to achieve its intended goals unless there are reasons to change them. There can be several reasons (e.g. changes in agent’s environment, imposition of social norms, communication from other agents) because of which an agent may choose to adopt an alternative goal.In this paper, we model an agent as a BDI agent whose activities are also governed by certain social norms. The use of social norms is justified because of the fact that agents do not function in isolation, rather as a society - a view which has been made possible due to technological breakthroughs like Internetand other forms of communication. We define three cognitive states corresponding to the mental attitudes (belief, desire and intention) and show that an agent can be influenced by affecting these cognitive states. In order to modify cognitive states we propose the use of different tones of communication. Further, we show the relevance of social norms which also control the goal-adoption behaviour of an agent.The rest of this paper is organized as follows : Section 2 provides a background to this area of research. Section 3 discusses an use of the process of influencing with the help of a scenario. Section 4 describes an agent model by highlighting its internal attributes. It also defines three cognitive states of an agent which are used in influencing an agent. Section 5 deals with a formal specification of the process of influencing. Section 6 typifies an agent’s behaviour into three categories which explains the behaviour of an agent when it is subjected to an influencing process. Finally, section 7 summarizes the contributions of this work.2. BackgroundThis section provides an informal overview of agent models proposed in [23,25,27] which serve as a basis of our perception of an agent.2.1 Notion of AgencyThough the concept of agent has occupied a key place in both artificial intelligence (AI) and mainstream computer science but a consensus has not yet been reached for the definition and composition of an agent. One of the definitions which looks quite reasonable is : An agent is an entity, situated in a changing environment that continuously receives perceptual input and, based on its internal mental state exhibits reactive or proactive behaviour that potentially changes the environment in which it is situated [25]. Depending on the requirements of applications, developers ascribe different attributes to the internal composition of agents. Two important notions that emerge so prominently are: a weak notion of agency and a strong notion of agency[32]. The weak notion basically deals with agent properties like autonomy, social ability, reactivity, and pro-activity. On the other hand, researchers particularly those in the field of Artificial Intelligence tend to ascribe mental attitudes to agents which are usually applied to humans. This forms the basis for strong notion of agency. In addition to these notions, other attributes of agency like rationality, benevolence, veracity, mobility have also been proposed. Shoham [27] characterizes an agent using mentalistic notions such as knowledge, belief, intention and obligation. Georgeff et al [15,23] investigates a particular type of agents, called BDI agents based on the view that belief, desire and intention are the three primary mental attitudes which capture the informational, motivational and decisional components of an agent respectively. Ascription of such notions which are usually used in connection with human behaviour to artificial artifacts like software agents looks quite legitimate as they are useful to express and understand human problem-solving behaviour. In an attempt to answer “which attributes are appropriate for representing an agent”, Wooldridge and Jennings [32] categorize the attitudes into two broad classes, viz., information attitudes and pro-attitudes. The information attitudes (beliefs and knowledge) are concerned with the information that an agent has about the world it occupies and the pro-attitudes (desires, intentions, obligations, commitments, choices etc.) are those that in some way guide an agent’s actions. Further, it is suggested that an agent must be represented in terms of at least one information attitude and one pro-attitude. Thus in our agent model we take belief as the information attitude, and both desire and intention as the pro-attitudes.2.2 Cognitive Social AgentIn [4], a Cognitive Agent has been defined as an agent who founds its decisions, intentions and actions on its beliefs. Thus the concept of cognitive agent is a product of the strong notion of agency. Some even go beyond the notion of cognitive agent and promotes a societal view of computation in which multiple agents interact with each other on various issues [11,22,31]. In such setups utility of social laws [20,28] has been advocated to ensure successful co-existence of agents. Thus Social Agents are those which operate in the presence of other agents and whose interaction patterns are governed by certain social norms. Concepts drawn from both social and cognitive agents define a Cognitive Social Agent whose functionality is defined based on the mentalistic attributes as well as on social norms.2.3 Agents in Influencing processInfluencing refers to an agent’s behaviour which is meant to motivate another agent towards the adoption of some goal of former’s choice. As agentsinteract with each other while pursuing their respective goals at some occasion or other one may try to influence another agent to make it adopt or abandon a goal. This type of agent interaction has been studied in [7] based on a model of dependence. There it is evident that dependence can be treated as a cause for an influencing process. Since in BDI agents adoption or abandoning of a goal is supported by one’s beliefs, in order to influence an agent one must first modify the target agent’s beliefs supporting those goals. This may lead to a situation where the influencing agent need to know the beliefs of a target agent to be influenced, and the target agent’s beliefs about the beliefs of the influencing agent and so on. However, we do not consider such a situation which leads to an infinite loop rather we assume that the beliefs of one agent are transparent to another for the purpose of our analysis. This enables us to assume that an agent can cognize the mental attitudes (beliefs, desires, intentions) of another agent during interaction which helps an influencing agent to adopt appropriate strategy to influence the target agent.2.4 Agent CommunicationAgents Communicate with each other through message passing. The messages which are usually exchanged are communicative acts of the type -informing, requesting, instructing, confirming, commanding persuading, warning etc. The use of such communicative acts has a basis on Speech act Theory [1,26]. A Speech act has two components, viz., a propositional content -describing the state of the world and an illocutionary force - indicating the strength of a speech act. In the literature speech acts have been categorized into various types like - assertives, directives,commissives,permissives,prohibitives, declaratives. Each type of speech act involves different presuppositions and has different effects. An agent intending to communicate to another agent with a purpose chooses appropriate speech act and sends a message. Such a message may have an intended effect on the receiver. The message is communicated in a predefined format of the type :<message> :: { sender: <sender-id>addressee: <addressee-id>message-id : <message identificationnumber>message-tone : <tone of message>content : < propositional content ofmessage >}A message-tone is one of those informing, requesting, instructing, warning, commanding, confirming etc.. A taxonomy of message tones can be found in [3]. The content is actually the subject matter of a message(propositional content). For example, a message-tone could be “requesting” while the message content is “provide service X”.3. An Application of Influencing3.1 OverviewIn this section, we analyze the process of influencing with the help of a shop floor scenario in a Production Management environment. Various aspects of the scenario are progressively introduced as the analysis progresses. We begin with an informal narration of the scenario and state the functional objectives of the agents involved. The shop floor scenario of a production unit is generally characterized by various production activities. There is a hierarchy of personnel who are involved in the process. One finds engineers, supervisors, and a number of operators in the shop floor. While the operators are directly involved with the operation of various equipment and machinery, the role of supervisors is to supervise the activities of the operators so as to meet the production targets. In turn supervisors are accountable to the higher level of management. Thus in order to meet production targets set by the management, supervisors employ different techniques to make operators work. In later sections, keeping this scenario in view we analyze the cognitive states of the agents (operators) for explaining the process of influencing.3.2 ScenarioHere, we focus on three typical situations in which a supervisor (SUP) tries to influence operators (OP1, OP2) towards his intended goals. The supervisor uses different communicative acts (with appropriate choice of tone) in order to influence OP1 and OP2 to adopt such goals in which the supervisor is interested. Situation 1Earlier, operators were eligible to avail a half day off after working 3 consecutive nights. Now, in order to encourage more operators to work at night with a view to increase volume of production the management decides to give one day off instead of half day. SUP informs this to operators in the following manner.SUP : Those who will work in 3 consecutive nights are eligible for one day off.OP1: Well, I am ready to work at night.Situation 2OP1 desires to go home and requests SUP for one week leave. SUP after knowing OP1’s desire for going on leave instructs him to complete job #4 (a job which OP1 committed to finish) in two days. Only then OP1 would be granted leave. Considering it impossible OP1 gives up his desire of going home. This is shown in the following conversation.OP1: Sir, I want to avail one week leave for going home.SUP : Finish job # 4 in two days, only then you will be granted leave.OP1 : Well, I won’t go now.Situation 3OP1 and OP2 were already granted leave for going home. Subsequently, SUP communicates an urgent message informing the visit of General Manager (GM) to their unit for an on-the-site inspection. Also SUP requests them to be present during the inspection. Considering urgency of the message OP1 gives up his intention to go home for the time being and requests SUP to grant him leave after the inspection is over. But OP2 does not agree to stay back because he gives more priority to his own goal of going home (perhaps for some important work). This is show in the following conversation.SUP:Operators ! All of you must be present tomorrow. GM is coming for inspection to our unit. OP1 :O.K. I shall stay back. Kindly grant me leave after the inspectionOP2: Sorry, I can’t stay back because I have to go home at any cost.In the above conversations we see that the supervisor employs different tones of communication at three different situations in order to achieve his goal. In situation 1, SUP simply informs management’s decision which comes as a promise of prize to operators. Through this SUP tries to influence operators to work at nights. In response to that OP1 agrees to work at night. Thus SUP comes out successful in influencing OP1. In situation 2, from the first line of the conversation SUP comes to know that OP1 has a desire to go home. Since SUP has the goal that job #4 must be completed by OP1, he employs a tone of instruction to influence OP1. SUP could succeed as OP1 tells that he won’t go. Finally, in situation 3, both OP1 and OP2 were almost ready to go home since they were granted leave. Considering the fact that both are almost committed to go home, SUP employs two different techniques simultaneously. He communicates an urgent message and at the same time requests them to stay back. OP1 considers the urgency of the message and at the same time positively responds to the request of SUP. Though OP2 realizes the urgency of the message but doesn’t yield to SUP’s request. Thus SUP succeeds in influencing OP1 but fails to do so with OP2. These situations are further analyzed in subsequent sections.4. Specifying Agents for InfluencingIn this section, we describe the internal attributes of an agent. Though we do not claim that our description of an agent is complete and objective, however we believe that the formalisms and properties introduced here are intuitive and serve our purpose for explaining the process of influencing. We also provide a formal description of our model by defining the cognitive states of an agent.4.1 The Agent ModelAn agent is considered to be a member of a multi-agent society. In addition to its own internal components an agent has an environment which defines the scope of its activities. Each agent is endowed with certain cognitive properties and is aware of certain predefined social norms. An agent’s knowledge base is supported by three basic components, viz., the environmental component Env, social component Soc, and cognitive component Cog (See Figure 1). The environmental component incorporates agent’s object-level knowledge about its environment such as knowledge about other agents-their capabilities, availability etc. The social component includes knowledge of certain relevant social aspects such as social relations, obligations, commitments, dependencies and set of social norms that help an agent to perform its activities in a socially acceptable and predictable manner. By ‘socially acceptable’ we mean that an agent does not hinder the activities of other agents, does not lie ( does not provide wrong information), cooperate with other agents whenever asked to do so, and the like. By ‘predictable’ we mean that an agent follows certain social norms while interacting with other agents in its society, for example beliefs of an agent constitute its cognitive resources. Besides that an agent may require other forms of resources to achieve its goals. The Cognitive Reasoner incorporates a local reasoning mechanism which takesa set of desires (that serves as a trigger to act) and generates a set of intentions. The reasoning is based on its own beliefs (supporting those desires) and the weightage it attaches to any other external communications received (relevant to those desires). The Actuator is a decision making mechanism which controls/decides the final action(s) of an agent at a particular point of time. The Actuator takes a set of intentions as input and considering one’s commitments, priorities and availability of resources (like time, space, communication channel) decides the way an agent should act.4.2 Defining the Cognitive StatesAs described in section 4.1 beliefs, desires, and intentions are three primary cognitive components which govern the behaviour of a BDI agent as regard to goal adoption. We think of a scenario where agents operate in the presence of other agents interacting with each other on various contexts. An agent perceives its environment through observations as well as by receiving explicit messages from other agents. As described earlier, beliefs are informational contents of an agent and are rooted on the information that an agent captures from its environment. The environment being dynamic, the information input to an agent may change over time so also the beliefs of an agent. Since desires are supported by one’s beliefs, desires may also vary with time. Finally, intentions which are rational desires and can be considered as a subset of desires, may also vary over time. This motivates us to define three states, viz., Belief state, Desire state, and Intentional state with explicit reference to time intervals.Belief StateAt a given time t an agent A may believe ϕdenoted as Bel t (A, ϕ) and it continues to believe so as long as there is no contradictory evidence (gathered through observation or received-messages) of greater credibility. Since an agent remains in a particular belief state for a period of time, however short the duration may be; we choose to denote it as: Bel ti,tj( A, ϕ), where the time elapsed between the two time points t i and t j (where t i < t j ) is the period during which agent A believes ϕ. The factors that characterize a belief state of an agent are its knowledge about own capabilities, capabilities of other agents, environmental information ( like the structure of agent society in which it is performing, information regarding entry and exit of agents into/from agent society) , and a set of social norms (like commitments , obligations, dependencies etc.). We denote a belief state with a tuple as :Bel ti, tj( A, ϕ) :: < C own , C other , Env, Soc > where C own is a list of activities the agent itself iscapable of performingC other is a table of agent_ids and their capabilities Env stores the structure ( flat, tree, graph ) that linksthe agents together. The structure controls agent -interaction pattern.Soc is a list of committed services, dependencyrelations and obligations.Adoption of a goal largely depends on an agent’s beliefs. For example, if an agent A has committed to provide service S to another agent B then A believes that it has to provide the committed service to B at a time mutually agreed, and hence decides to adopt the goal of performing necessary actions in order to provide service S. On the other hand B also believes the service commitment of A ( possibly communicated through a commitment message ) and accordingly adopts a goal of its own that uses service S.Desire StateDesires can arise from beliefs. Following similar arguments as given while defining a belief state, we denote a desire state of an agent as Des t i , t j ( A, ψ ) ,which means that agent A has desire ψ during the time interval < t i ,t j >. A desire state is characterized by a set of goals which an agent desires to achieve. This desired-goal set comprises of an agent’s own goals supported by its beliefs and also goals of others which it considers for adoption on request (through service requests received as messages) : Thus a desire state is denoted as:Des t i , t j ( A , ψ ) :: < G desired >where G desired is an agenda of goals during the time interval <t i ,t j > which agent A desires to achieve. In fact G desired comprises of a set of agent A’s own goals supported by its beliefs, and also such goals which A adopts at the request of other agents. To give an example, if an agent in a manufacturing scenario believes that a particular type of alarm indicates a short circuit then it immediately adopts the goal to shut down the machine. Similarly, when an agent receives a service request message then it may adopt the goal of executing a procedure that helps in realizing the service.Intentional StateIntentions can be treated as desires which an agent believes to be achievable considering the availability of required resources. We denote anintentional state of an agent as Int t i , t j (A, λ) which means that agent A intends λ during the time interval < t i , t j >. When an agent commits to realize a set of desired goals (that it had in its desire state)considering priorities P, commitments Com , and resource availability R av ; such committed goals define its intentional state which we denote as G intended . Thus we see that G intended ⊆ G desired . An intentional state is denoted as :Int t i , t j ( A , λ ) :: < G intended >where G intended is an agenda of goals which agent A intends to achieve. This intended goal- agenda is sorted taking into account priorities, commitments, and availability of resources during the interval < t i , t j >.For example , when an agent in its desire state desires to achieve a goal α and also believes that it has the capability to do so with the available resources; then it adds α to its agenda of intended goals. Similarly, when an agent receives a message from another agent regarding some goal β then agent A may decide to add it to or delete from its goal-agenda after proper reasoning.5. The Process of InfluencingIn this section , we turn our attention to a formal specification of the process of influencing and show how it can act on the three different cognitive states of an agent. We also discuss on the roles of message tones and social norms in process of influencing. We will base our analysis on the following postulate :Intended goal-agenda of an agent can not be manipulated by another agent directly. One way of modifying the goal-agenda is influencing, which can be realized by bringing in a change in the beliefs and the environment of a target agent.Corollary 1 : An agent can be influenced to adopt a goal on being supported with sufficient beliefs.Corollary 2 : Goal priority , social norms and availability of resources are parameters used to update desired goals to intended goals.Ordinarily an agent behaves according to its own beliefs, desires and intentions. It adopts goals which are supported by its beliefs and schedules them according to its own priorities . However in a multi-agent set up,an agent is exposed to external influences aimed at modifying its goals. External influences on an agent can be made possible through message communications or by manipulating the environment in which the target agent is situated.5.1 Influencing and Cognitive StatesBelow, we show how an agent can be influenced when it is in any one of the three cognitive states. We explain process of influencing with reference to the three situations narrated in the example scenario of section 3.Modifying a Belief StateIn section 4.2, factors that characterize a belief state of an agent are described. An agent may modify its belief state due to two reasons: 1) based on some external stimuli (receiving messages of the type assertive, and declarative), 2) by introspection (i.e.reasoning over a given situation). We denote a state transition from one belief state to another belief state asBel t i , t j ( A , ϕ ) → Bel t j , t k ( A , ϕ′ )where ϕ is a set of beliefs which supported agent A’s goals during the time interval <t i ,t j > and ϕ′ is a modified set of beliefs which would serve as a basis for goal adoption during <t j ,t k >. An agent causing a change in the belief set of another agent can influence the latter to adopt a new goal or refrain from an earlier goal.Example : (situation 1)Here, SUP’s message initiates a process of influencing with a goal of encouraging operators to work at nights.This message modifies the earlier belief state of OP1 as indicated below.Belief of OP1 prior to receiving SUP’s message : “One is eligible to avail half day off after working 3consecutive nights ”.Modified belief of OP1 after receiving SUP’s message :“One is eligible to avail one day off after working 3consecutive nights ”.Based on this modified belief, OP1 adopts the goal of working at night. OP1 continues to act with this belief until some change in the rules for availing off day is communicated to him.Modifying a Desire StateThe desire state of an agent is characterized by a set of goals which an agent would like to achieve. All desires need not be rational and an agent may have conflicting and unrealistic desires. Another agent may take advantage of this adhoc state and try to influence an agent for addition or deletion of a goal to/from its agenda of goals. If during the time interval <t i ,t j > anagent’s desire state is given by Des t i , t j (A , ψ) where agent A has a set of desired goals ψ, then due to possible change in beliefs, A may adopt new desires or abandon some; thus having a modified set of desires ψ′which may persist for a time interval <t j ,t k >. A state transition from one desire state to another desire state can be denoted as :Des t i , t j ( A , ψ ) → Des t j , t k ( A , ψ′ )Example : (situation 2)OP1 had a desire to go home. But SUP initiated an influencing process with the instruction (“complete Job #4 in two days”) so as to modify the desire state of OP1.As a result OP1 abandons his goal of going home.Desire of OP1 before the conversation: “To go home”Desire of OP1 after the conversation: “Not to go home ”OP1 continues with his modified desire state (i.e. not to go home) until he completes job #4.Modifying an Intentional StateAn agent in an intentional state is committed to achieve a goal, however this state can be modified by manipulating goal priorities ( i.e. by sending urgency messages) as well as resources (e.g. informing availability or non availability of resources). Thus an agent with an intended goal set λ during a time interval <t i ,t j > can be influenced by communicating to it appropriate message(s) such that it adopts a modified set of intended goals λ′ which may persist for a time interval <t j ,t k >. We denote a state transition from one intentional state to another intentional state as :Int t i , t j ( A , λ ) → Int t j , t k ( A , λ′ )Example : (scenario 3)OP1 was granted leave and was committed to go home.Subsequently, SUP initiates a process of influencing by communicating an urgent message (“ GM is coming for inspection”) with a goal that OP1 should stay back.This message acts on the intentional state of OP1. As a result, OP1 considering the urgency of the message abandons his intended goal of going home for the time being.Intention of OP1 before receiving the message : “To go home ”Intention of OP1 after receiving the message : “Not to go home for the time being ”As long as GM’s inspection is on progress, OP1continues with its modified intention of “not going。