Overview of Jason — MASWS Code Examples 0.4 documentation Navigation index MASWS Code Examples 0.4 documentation » Table Of Contents Overview of Jason Setting up Jason Setting up the Environment A Brief Overview of an AgentSpeak Agent Some sample AgentSpeak(L) Agent1 Agent2 This Page Show Source Quick search Enter search terms or a module, class or function name. Overview of Jason¶ Jason is an interpreter for AgentSpeak programs, and a framework to create environments for the development and testing of multi agent systems. You will not need to be familiar with the full power of Jason however. The website for Jason is http://jason.sourceforge.net and it is the best place to start for finding documentation and example code. In particular the documentation section of the site contains links to the manual and a getting started tutorial, both of which are essential reference documents. Setting up Jason¶ An IDE is provided for the easy editing of AgentSpeak, running of the environment and debugging. To set it up simply follow the instructions below, taken from the getting started tutorial (which has more info, and pictures). Download Jason from http://jason.sourceforge.net. Extract the archive to a folder in your userspace. Something like | tar xzf Jason-1.2.tgz should do the trick. Execute Jason by running ./jason.sh from the bin directory. You will probably need to set up the location of your Java JDK. Go to the menu Plugins -> Plugins Options -> Jason. On a DICE machine, “Java Home” should be set to /usr/lib/jvm/java/ At this stage I would encourage loading some of the examples and running them, to get an idea of how things work. The guides online may be of some assistance here. Setting up the Environment¶ The steps below will take you through loading and running the assignment code: Download the Assignment 2 code, and decompress it, e.g. with: unzip masws-assign2.zip. Start Jason, and load up hotels.mas2j. You will then be able to load the .asl files for travel_agent, hotel_agent and bnb_agent. The iactions directory contains the Java code for the checkDB internal action. Edit your code as appropriate, and run or debug with the buttons in the bottom right area of the IDE. The Jason IDE will handle compiling the Java code for you, and any files in lib will be in the classpath. If you wish to add other directories to your classpath, rename bin/build.xml to bin/c-build.xml and edit as appropriate. For example, on a DICE machine to add the Jena libraries to the classpath you would add the lines:
to the project.classpath section of your bin/cbuild.xml file. A Brief Overview of an AgentSpeak Agent¶ This is a very brief overview, for further information it is strongly recommended that you read the Jason documentation and see the examples. The main components of an agent are beliefs, intentions and plans. Beliefs either come from percepts, and are updated automatically each reasoning cycle, or are added from plans. They are expressed as predicates, which may be of arity-0. An example of a position belief might be pos(2,3). Plans are of the following form: triggering-event : guard
<- plan_step;
plan_step. triggering-event: The triggering-event defines which events may initiate a plan. It could be internal, from plans, or external, from percepts. It can be addition, denoted by + or removal denoted by -. It may be either a goal or a belief. So for example +!start would trigger on the addition of a start achievement goal. guard: A guard is a conjunction or disjunction of beliefs, logical formulae and certain built-in special predicates, such as .random(N). An example of a guard depending on the position would be pos(X,Y) & (X == 10). Note that variables must begin with an uppercase letter, while lowercase or numbers are constant. The _ is a “don’t care” variable which unifies with anything. plan step: Plan steps may be 0 or more steps, seperated by ; and terminated with a full-stop. These can be actions, in the form do(action), or goals to achieve, in the form of +!goal. This is an incomplete description of AgentSpeak; please see the documentation for more information. Some sample AgentSpeak(L)¶ To get you started, here are some simple AgentSpeak(L) plans: +!send(Message, Agent) : true
<- .send(Agent, tell, Message)
+!broadcast(Message) : true
<- .broadcast(tell, Message). The first sends Message to agent Agent. This will result in the belief Message being added to Agent‘s belief base. The second plan is to broadcast a message. A simple example of code for two agents to communicate could be as follows: Agent1¶ Agent1 sends a hello to all agents, and prints “yay!” with every response it gets: !go. //this is an initial goal
+!go : true
<- .broadcast(tell,hello).
+hello_from(Agent) : true
<- .println("Yay! Heard from: ", Agent). Agent2¶ Agent1 waits for a hello, and when it receives one, it responds to whoever sent it: +hello[source(A)] : .my_name(Me)
<- .send(A, tell, hello_from(Me)). And finally some simple code to wait for 4 replies: /* Example recursive code to wait for 4 replies
of the form "reply(X,Round)" */
// A counting rule to make this easier
// Has everyone replied this round?
done_round(R) :-
.count(reply(X, R), 4).
+!check(R) : done_round(R)
<- .println("Got 4 replies!").
//still waiting on replies case (we've proposed but not got all replies yet)
+!check(R) : true
<- .wait(250); //wait 250ms before checking again.
!check(R). Navigation index MASWS Code Examples 0.4 documentation » © Copyright 2012, Ewan Klein. Created using Sphinx 1.1.2.
