1 Properties of agents: Properties of agents: rationality - PDF document

2. Single-agent systems 2.1 Formal Definitions and Properties n Term “ agent ” used with many different meanings: Our goal: rather broad definition ● Agent of an agency (see James Bond) Definition : Agent ● Agent as a person acting on behalf of another An agent Ag is a tuple Ag = ( Sit , Act , Dat ,f Ag ) where person n Sit is a set of situations Ag can be in ● Agent as a substance achieving some change/ effect n Act is a set of actions Ag can perform n Even in Computer Science no agreement! n Dat , Ag ’ s internal data, is the set of possible value n Also under discussion if there is such a thing as a combinations Ag ’ s internal data areas can have single-agent system (agent acts in environment and n f Ag : Sit ✕ Dat ➔ Act is the agents decision function some see environment as a second agent) From outside, Ag seems to be a “ function ” g Ag : Sit ➔ Act Multi-Agent Systems Jörg Denzinger Multi-Agent Systems Jörg Denzinger Remarks (I) Remarks (II) n g Ag is not really a function, it can be a relation! n Our definition is really broad: ● If we want to use observations (from outside) to ● Every computer program fulfills it. predict the behavior of an agent, we can be in ● Human beings trouble! ● Animals ● Even if we know the real function f Ag ,predictions ● Lifeless objects are not easy if we do not exactly know the actual F Some authors require additional properties from an values of the agent ’ s internal data areas. agent, � ● Many problems that we have with multi-agent but different authors require different properties and systems have their roots in this problem! some of them cannot be easily formalized! Multi-Agent Systems Jörg Denzinger Multi-Agent Systems Jörg Denzinger Properties of agents: � Properties of agents: � autonomy knowledge-based cogito ergo sum An agent is autonomous , if it tries to achieve goals on its An agent acts knowledge-based , if it can justify its actions own without direction from other agents. An autonomous agent can react even when encountering unforeseen events. Multi-Agent Systems Jörg Denzinger Multi-Agent Systems Jörg Denzinger 1

Properties of agents: � Properties of agents: � rationality reflectivity and reactivity (I) $ $ $ ? $ $ $ $ An agent is and acts rational , if its behavior is oriented An agent acts reflective , if it bases its decisions on how to on fulfilling its goals as completely and as good as act very much on the actual value from Dat . possible. Multi-Agent Systems Jörg Denzinger Multi-Agent Systems Jörg Denzinger Properties of agents: � Properties of agents: � reflectivity and reactivity (II) social No ! Else it acts reactive . An agent acts social , if it does not hinder other agents in their actions Multi-Agent Systems Jörg Denzinger Multi-Agent Systems Jörg Denzinger Some formal properties of agents: � action language of an agent Remarks bbaa abaa n Does this mean an agent can “ do ” only one thing at a bba aba time? � bb ab No! � b a We model performing actions a 1 , a 2 , and a 3 at the same time by performing action a 1,2,3 that is defined as performing a 1 , a 2 , and a 3 at the same time. n In most cases, we are interested in sequences of Let Ag = ( Sit , Act , Dat ,f Ag ) be an agent. A set L Ag ⊆ Act * is actions of agents (i.e words of the action language), an action language to Ag , if for each word w ∈ L Ag not only single actions/decisions. holds: each start word v of w (i.e. w =vu) is element of L Ag Multi-Agent Systems Jörg Denzinger Multi-Agent Systems Jörg Denzinger 2

� � Some formal properties of agents: � Some formal properties of agents: � deadlock free liveliness S O S ! ? Let Ag = ( Sit , Act , Dat ,f Ag ) be an agent with action An agent Ag = ( Sit , Act , Dat ,f Ag ) with action language L ag language L Ag . An action t ∈ Act is alive in L Ag , if for all is called deadlock free , if there is no w ∈ L Ag such that w ∈ L Ag holds: there is a v ∈ Act * with wvt ∈ L ag . for all v ∈ Act *holds: wv ∉ L Ag . Ag is called alive , if for all t ∈ Act t is alive in L Ag . Multi-Agent Systems Jörg Denzinger Multi-Agent Systems Jörg Denzinger Some formal properties of agents: � fairness Remarks n The properties described first obviously are of a certain relevance when looking at multi-agent systems. n The formal properties will be needed later to show a very basic problem of multi-agent systems: � Let Ag = ( Sit , Act , Dat ,f Ag ) be an agent with action language L Ag . Ag is fair , if for all infinite words w Even if all agents in a MAS have a certain property, then the MAS as a whole is not guaranteed to have with all start words of it within L Ag and all t ∈ Act this property. � holds: � If there are infinitely many start words v i of w, such So, do not immediately forget these properties. that v i t ∈ L Ag , then t appears in w infinitely often. Multi-Agent Systems Jörg Denzinger Multi-Agent Systems Jörg Denzinger 3