3APL

An Abstract Agent Programming Language or Artificial Autonomous Agents Programming Language or 3APL (pronounced triple-A-P-L) is an experimental

Belief-Desire-Intention

(BDI) approach.

Overview

3APL was developed and is maintained by a team at the

papers and conferences, and at least 4 theses

.

Platform

The 3APL

3APL-M "Toymaker

", has also been released.

Language

The 3APL language is relatively simple. The syntax has basic

variables cannot be created except by calling plug-in methods or belief/goal conditions, iterative

counter loops can be constructed using a combination of WHILE-DO loops, beliefs and capabilities.

A 3APL agent contains formal definitions of agent beliefs, capabilities, goals and plans. Specifically, there are six skeletal blocks that must be defined.

PROGRAM "agent"
BELIEFBASE {}
CAPABILITIES {}
GOALBASE {}
PLANBASE {}
PG-RULES {}
PR-RULES {}

The beliefs, defined using Prolog syntax, are used to remember information and to perform logical computations. Beliefs can be read by one another, edited by the capabilities, and read by conditional statements in the plans. The initial beliefs of an agent can be defined in its belief base.

BELIEFBASE {
	status(standby).
	at(0,0).
	location(r1,2,4).
	location(r5,6,1).
	dirty(r1).
	dirty(r5).
}

Capabilities define the prerequisites and effects of actions in a STRIPS-like format, reading preexisting beliefs, removing some using the NOT operator, and adding new ones by stating them.

CAPABILITIES {
	{status(S1)} SetStatus(S2) {NOT status(S1), status(S2)},
	{at(X1,Y1)} NowAt(X2,Y2) {NOT at(X1,Y1), at(X2,Y2)},
	{dirty(R)} Clean(R) {NOT dirty(R)}
}

Goals are also defined using Prolog syntax, and new goals can be adopted during runtime. Initial goals are defined in the goal base.

GOALBASE {
	cleanRoom(r1).
	cleanRoom(r5).
}

Each goal ideally has associated goal planning rules, its PG rules, which serve as an abstract plans and are called from the goals as long as their guard conditions are met.

PG-RULES {
	cleanRoom(R) <- dirty(R) | {
		SetStatus(cleaning(R));
		goTo(R);
		clean(R);
		SetStatus(standby);
	}
}

The PG rules in turn can call plan revision rules, or PR rules, which serve as subroutines, and can be called upon to execute lower level and/or repetitive tasks as long as their guard conditions are met. Initial plans are defined in the plan base, executed at the beginning of the deliberation cycle.

PLANBASE { SetStatus(started); }
PR-RULES {
	goTo(R) <- location(R,X,Y) AND NOT at(X,Y) | {
		NowAt(X,Y);
	}
	clean(R) <- location(R,X,Y) AND at(X,Y) | {
		Clean(R);
	}
}

External methods may be called to access the environments modeled in the plug-ins. However,

predicate logic

.

Java("JanitorWorld", moveNorth(), M);

Agents can also communicate with one another using Send commands. When a piece of information X is sent with the performative P from agent A to agent B, the sending action is recorded in A's belief base as sent(B,P,X) and is registered in B's belief base as received(A,P,X).

Send(Partner,inform,dirty(R));

Download

3APL is available for download at the University of Utrecht's 3APL website, packaged with sample lone and communicative agents, and a discrete multi-agent foreground environment plug-in called BlockWorld.

External links

3APL Homepage