Progress in BDI Logic Programming with AgentSpeak(L) Rafael H. Bordini R.Bordini@csc.liv.ac.uk Department of Computer Science University of Liverpool, U.K.
Summary Overview of AgentSpeak(L) AgentSpeak(XL) Interpreter Asymmetry Thesis Principles in AgentSpeak(L) AgentSpeak(F) Verification Ongoing and Future Work 29/11/02 Dagstuhl Seminar p.2/65
Overview of AgentSpeak(L)
AgentSpeak(L) Programming language for BDI agents (faithful to the original conception of the BDI architecture) Natural extension of logic programming (neat notation) Proposed by Rao (MAAMAW 1996) Logical, computable, agent oriented programming language Bridging the gap between BDI theory and practice Abstract interpreter was further formalised using Z by d’Inverno and Luck Joint work with: Rodrigo Machado (UFRGS) First prototype interpreter: SIM Speak, based on SIM AGENT 29/11/02 Dagstuhl Seminar p.4/65
✡ ☞ ☎ ✆ ✆ ☎✆ ✂ ✁ ✟ � ☛ ☛ ☛ ☎ ✆ ✆ ☎✆ ☛ ✌ � ☛ Syntax (I) If is a predicate symbol, and ✁✄✂ ✁✞✝ are (first-order) terms, ✁✠✝ is a belief atom Ground belief atoms are base beliefs If is a belief atom, and are belief literals Belief literals are beliefs If and are beliefs, so is 29/11/02 Dagstuhl Seminar p.5/65
✆ ✆ ✂ ✆ ✡ ✆ � ✁ ☎ ✡ ✟ ☎✆ � ✞ ✡ ✡ � ✡ � ✂ ✡ � ✡ ✁ ✟ ✆ ☎✆ ✁ ✝ ✟ ✟ ✟ ✡ ✆ � ✂ ✂ ✞ ✁ ✡ ✆ ✟ � ✁ ✞ ☎ � � ✡ ✆ ✡ ✆ ✂ ✡ ✟ ✁ ✂ ☎✆ ✆ ✆ ☎ ☎ ✂ ✆ ✁ ✄ ✟ � ✁ ✝ ☎ ✁ ☎ ✆ ✆ � ☎✆ � ☎ Syntax (II) If is a predicate symbol, and ✁✄✂ are terms, ✁✠✝ ✁✠✝ and are goals ‘ ’ denotes achievement goals ‘ ’ denotes test goals ✟ ✝✆ ✟ ✝✆ ✟ ✝✆ If is a belief atom, and are goals, then ✟ ✝✆ ✟ ✝✆ ✟ ✝✆ , , , , and are triggering events ✁✄✂ If is an action symbol and are first-order ✁✞✝ terms, then is an action 29/11/02 Dagstuhl Seminar p.6/65
✂ ✝ ✆ ✆ ✆ ☎ ✂ ✝ ✁ ✄ � � ✂ ✂ ☎ ✆ ✆ ☎✆ ✂ ✂ ✄ ✁ ✁ � ☎ Syntax (III) If is a triggering event, is a belief (plan context), and are goals or actions (plan body), then is a plan (where is called the plan’s head) An AgentSpeak(L) program is specified by a set of initial base beliefs and a set of plans 29/11/02 Dagstuhl Seminar p.7/65
✟ ✂ ✂ ✝ � ✂ ✠ ✂ ☎ ✡ ✂ ✂ ☎ ✂ ✁ ✆ ✆ ☎ ✔ � ✘ ✞ AgentSpeak(L) Interpreter An intention is as stack of partially instantiated plans An event is a pair , where is a triggering event and is an ✁✄✂ intention If the intention is the true intention , the event is called an external event , otherwise it is an internal event An AgentSpeak(L) agent is defined by a tuple ☛✌☞ ☛✌✍ ☛✏✎ Selection functions: ✑✓✒ selects an event from set ✑✓✕ selects an option (i.e., an applicable plan) ✑✗✖ selects an intention from the set 29/11/02 Dagstuhl Seminar p.8/65
AgentSpeak(L) Agent Beliefs Belief Base Beliefs 2 Plan 1 Perception Library BRF Events S E External Events Events Selected Event Internal Plans Events 3 Unify Event Beliefs Relevant Plans Beliefs Selected 5 6 4 7 Intention Unify Execute Action S S I Context O Intention Applicable Intended Plans Means Intentions Update Intention New Intentions Push Intention Subplan ... New New 29/11/02 Dagstuhl Seminar p.9/65
AgentSpeak(XL) Interpreter
Introduction Joint work with: Ana Bazzan, Rafael Jannone, Daniel Basso, Rosa Vicari (UFRGS) and Victor Lesser (UMass) Combining Logic-Based and Decision-Theoretic Agent Frameworks Practical (initial) contribution: using decision-theoretic task scheduling (TÆMS/DTC) to improve intention selection in AgentSpeak(L) Selection functions were taken for granted Greater expressiveness applications where quantitative reasoning is natural control over an agent’s set of intentions 29/11/02 Dagstuhl Seminar p.11/65
☎ � ✆ ✆ ✆ ☎ ✂ ✝ ✂ ✁ ✂ � ✆ ✟ ✁ ✁ ✁ ✂ ✄ ☎ ✂ ✁ ✂ ✡ ✞ ✁ � ✝ ✡ ✁ ✞ � ✁ ☎ ✡ ✆ ✆ ✆ � � ✄ ✟ Language Extensions (I) Addition/deletion of beliefs (in plan bodies) ✟ ✝✆ ✟ ✝✆ Recovering from plan failure: , Special action for speech acts based communication: .send (I.F.: inform , ask , achieve , know-how , deny ) Plans have labels: Internal actions: 29/11/02 Dagstuhl Seminar p.12/65
Language Extensions (II) Internal actions: Run locally by the interpreter, do not affect the environment (i.e., they take effect immediately) Can be used in the context as well as in the body of a plan Side effects: if they appear in the context of a relevant plan, they are executed even if the plan is not applicable Separate libraries for different types of extensions Empty library name: access to the standard library (arithmetic and relational operators) 29/11/02 Dagstuhl Seminar p.13/65
Interpreter Extensions Access to libraries of actions List of (generic) properties associated with each plan in the set of intentions (in a dynamic way) Interpreting illocutionary forces and updating the appropriate data structures Unification algorithm allows uninstantiated variables in negated literals Events with no applicable plans can be either discarded or suspended (select more than one at a cycle) External actions may fail 29/11/02 Dagstuhl Seminar p.14/65
✠ Integrating with DTC The DTC scheduler produces alternative sequences of method (action) execution for a given TÆMS task structure it attempts to satisfy the criteria (quality, duration, and cost), relationships and deadlines as much as possible We create a TÆMS task structure where the methods are plan labels (intended means) Programmers can set specific values for the scheduling criteria, relationships and deadlines of each plan (using internal actions from a specific library) The schedules returned by DTC for the TÆMS t.s. representing defines the order in which to select intentions 29/11/02 Dagstuhl Seminar p.15/65
Free Software – Download http://protem.inf.ufrgs.br/cucla 29/11/02 Dagstuhl Seminar p.16/65
Asymmetry Thesis Principles in AgentSpeak(L)
Introduction (I) Joint work with: ´ Alvaro F. Moreira (UFRGS) Rao aimed at “bridging the gap” between theory and practice of BDI agents Proof system (sketched) for AgentSpeak(L) with which to prove BDI properties of agents (not done) Example of such properties are Rao & Georgeff’s principles based on Bratman’s Asymmetry Thesis 29/11/02 Dagstuhl Seminar p.18/65
Introduction (II) Showing which of the asymmetry thesis principles apply to any AgentSpeak(L) agent An initial contribution towards more formal grounding for BDI programming Definitions for what the three mental attitudes expressible in BDI logics mean for AgentSpeak(L) agents (based on its structural operational semantics) A framework for proving other BDI properties of AgentSpeak(L) 29/11/02 Dagstuhl Seminar p.19/65
Motivation The asymmetry thesis principles express rational properties in respect to the mental attitudes of the BDI framework, and in AgentSpeak(L) are relevant for: Providing further insight into the language itself Informing designers of AgentSpeak(L) agents Defining the BDI logic to which AgentSpeak(L) corresponds 29/11/02 Dagstuhl Seminar p.20/65
Asymmetry Thesis Bratman’s Asymmetry Thesis basically says two things: it is irrational for an agent to intend to do an action and also believe that it will not do it ( intention-belief inconsistency ) it is rational for an agent to intend to do an action but not believe that it will do it ( intention-belief incompleteness ) Rao & Georgeff added: it is rational for an agent to believe that it can do an action without necessarily intending it ( belief-intention incompleteness ) 29/11/02 Dagstuhl Seminar p.21/65
✆ ✂ ✝ ✞ ✂ ✆ ✆ � ✁ ✁ � ✆ ✆ ✄ ✞ ✄ ✄ ✆ ✂ ✠ � ✁ ✝ ✆ ✁ ✝ � ✂ ✄ ✆ ✆ ✠ ✆ ✆ ✝ � ✁ ✆ ✁ ✆ � ✠ ✂ ✞ ✄ ✆ ✁ ✠ � ✁ ✝ ✆ ✆ ✝ ✁ � ✆ ✠ ✠ � ✆ Asymmetry Thesis Principles Label Principle ✂☎✄ AT1 INTEND BEL ✝✟✞ ✂☎✄ ✂☎✄ AT2 INTEND BEL ✂☎✄ ✂☎✄ AT3 BEL INTEND ✂☎✄ AT4 INTEND DES ✝✟✞ ✂☎✄ AT5 INTEND DES ✂☎✄ AT6 DES INTEND ✂☎✄ AT7 DES BEL ✝✟✞ ✂☎✄ ✂☎✄ AT8 DES BEL ✂☎✄ ✂☎✄ AT9 BEL DES 29/11/02 Dagstuhl Seminar p.22/65
☎ ✑ ✍ ✎ ✏ ✘ � � ✁ ✂ ✟ ✆ ✒ ✖ � �✁ ✓ ✂ ✟ ✓ ✆ ✖ ✗ ✠ ☎ ✆ ✌ ✂ ✂ �✁ ✂ ✂ ✄ ✞✆ ✟ � ✠ ✂ ☞ ✝ ✡ ✂ ✠ ✂ ✡ ✞ ✂ ☛ ✂ Preliminaries From the SOS of AgentSpeak(L): ☎✝✆ Agent: Circumstance is a tuple set of intentions set of events the set of actions The semantic rules define a transition relation ✟✕✔ refers to component of C (similarly for others) The intention with plan on top of is denoted by 29/11/02 Dagstuhl Seminar p.23/65
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