Software Agent Computing. Agent Mobility

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Quentin Arnold
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1 Software Agent Computing Agent Mobility

2 Planning mobility roadmap Agent mobility = to migrate or to make a copy (clone) itself across one or multiple network hosts Support for mobility in JADE: a set of API classes and methods, a mobility specific ontology, MobilityOntology, contained in the package jade.domain.mobility. Moving Agent class in the package jade.core contains methods: domove(), beforemove(), domove is called either by the Agent Platform or aftermove(), by the agent itself to start a migration process doclone(), beforeclone() Cloning afterclone(). To move an agent, you just need to call the method domove(location) public void domove(location destination) domove() just changes the agent state to AP_TRANSIT. The actual migration take place asynchronously.

3 Mobility in JADE: intra and inter Intra-platform mobility is that, mobile agent can navigate across different agent containers but it is confined to a single JADE platform Inter-platform mobility provides agent with navigating among Agent Platforms FIPA defines extensions that are necessary to the AMS to support mobility. JADE containers are not FIPA compliant (FIPA does not specify them) It should be noted that the concept of an AP does not mean that all agents resident on an AP have to be co-located on the same host computer. * Therefore FIPA does not specify intra-platform migration JADE supports intra-platform migration by adaptation of interplatform migration specification JADE does not support inter-platform mobility, but Migration Add- On does:

4 Mobility in JADE weak or strong? not-so-weak mobility Status: an agent have to wait before currently scheduled behaviour finishes its cycle JADE agents can migrate in the middle of a conversation and a programmer can exploit the behaviour composition capability in order to define an arbitrarily fine-grained sequence of states in which an agent is allowed to migrate move to a remote container (possibly on a different host) restart its execution there from the exact point where it was interrupted Code: If the code of the moving agent is not available on the destination container it is automatically retrieved on demand An agent must be Serializable in order to be able to move Mobility can be self-initiated through domove() of the Agent class forced by the AMS (following a request from another agent) Agent cloning is also available - method doclone()

5 Tricky point Location (1) You cannot create a Location object by yourself AMS the Boss: All platform management actions (creating/killing agents, killing containers...) are under the control of the AMS Other agents can request the AMS to perform these actions by using The Fipa-Request Interaction Protocol The SL language The JADE-Agent-Management ontology and related actions The AID of the AMS can be retrieved through the getams() method of the Agent class

6 The tricky point - Location(2) Ask AMS by sending it a REQUEST with content or WhereIsAgentAction allows to obtain the location of a given agent; parameter - the identifier of the agent that your are querying the location via method setagentidentifier(aid) QueryPlatformLocationsAction - allows to obtain all available locations within a given platform. It takes no parameter) package jade.domain.jadeagentmanagement

7 AMS as White Pages Services Scenario 1 Agent A asks AMS about all possible containers in the AP Agent A receives set of locations from AMS Agent A migrate to the randomly chosen location Scenario 2 Agent A asks AMS about location of the agent B Agent A receives the response from AMS about location Agent A migrate to the location of agent B Let s talk about ontology

8 Semantic of communication in JADE Documentation: JADE Tutorial Application-defined Content Languages and Ontologies, API documentation (javadoc): jade.content package and subpackage Sample code: examples.content package in the examples included in the JADE distribution

9 Agent Communication Info A B Inside the ACL message, Info is represented as a content expression consistent with a proper content language (e.g. SL) and encoded in a proper format (e.g. string). Both A and B have their own (possibly different) way of internally representing Info. Example: there is a person whose name is John and who is 35 years old (Person :name John :age 35) class Person { String name; int age; public String getname() {return name; } public void setname(string n) {name = n; } public int getage() {return age; } public void setage(int a) {age = a; }. }

10 Handling Content Expression A B A needs to convert his internal representation of Into the corresponding ACL content expression representation and B needs to perform the opposite conversion. B should also perform a number of semantic checks to verify that Info is a meaningful piece of information, i.e. that it complies with the rules (for instance that the age of John Is actually an integer value) of the ontology by means of which both A and B ascribe a proper meaning to Info

11 Main Elements of Communication content manager object of the ContentManager class included in the jade.content package received through the getcontentmanager() method content manager delegates the conversion and check operations to an ontology (i.e. an instance of the Ontology class included in the jade.content.onto package) and a content language codec (i.e. an instance of the Codec interface included in the jade.content.lang package)

13 Types of elements an ontology In detail, the types of elements an ontology deals with are defined as follows: Concepts are expressions that indicate entities that "exist" and that agents talk and reason about. Predicates are expressions that say something about the status of the world and usually evaluate to true or false. AgentActions are expressions that indicate something that can be executed by some agent.

14 Define semantical structure of message content. Content represents the domain dependent component of the communication. REQUEST :sender (agent-identifier :name :receiver (set (agent-identifier :name :content (( action (agent-identifier :name (where-is-agent (agent-identifier :name )) :language FIPA-SL0 :ontology JADE-Agent-Management :protocol fipa-request ) Denotes the encoding scheme of the content of the action. Brings representation of message, e.g FIPA SL or it subsets (SLO, SL1). Denotes the ontology which is used to give a meaning to the symbols in the content expression. An ontology gives meanings to symbols and expressions within a given domain language.

16 (REQUEST... :content (( action (ActorOfAction) (ActionName (ActionParameters)) ))... ) (REQUEST :sender (agent-identifier :name da1@zadig:1099/jade) :receiver (set (agent-identifier :name ams@zadig:1099/jade)) :content (( action (agent-identifier :name ams@zadig:1099/jade) (where-is-agent (agent-identifier :name Peter@Zadig:1099/JADE)) )) :language FIPA-SL0 :ontology JADE-Agent-Management :protocol fipa-request Summary: The sender requests the receiver to perform some action Message content: An action description Description: The action can be any action the receiver is capable of performing: pick up a box, book a plane flight, change a password etc. An important use of the request act is to build composite conversations between agents, where the actions that are the object of the request act are themselves communicative acts such as inform

17 (INFORM.. :content (( result ( action (ActorOfAction) (ActionName (ActionParameters)) ) (ResultOfAction) ))... ) (INFORM :sender (agent-identifier :name ams@zadig:1099/jade) :receiver (set (agent-identifier :name da1@zadig:1099/jade)) :content ((result (action (agent-identifier :name ams@zadig:1099/jade) (where-is-agent (agent-identifier :name Peter@Zadig:1099/JADE)) ) (set (location :name Container-1 :protocol JADE-IPMT :address Zadig:1099/JADE.Container-1 )) )) :reply-with da1@zadig:1099/jade :language FIPA-SL0 :ontology JADE-Agent-Management :protocol fipa-request

Handling content expression Creating the Ontology (vocabulary and semantic) Defining the schemas (ontology elements) Defining the corresponding Java Classes Handling

18 Handling content expression Creating the Ontology (vocabulary and semantic) Defining the schemas (ontology elements) Defining the corresponding Java Classes Handling content expressions as Java objects Using the ContentManager to fill and parse message contents Ontologies can be created with Protégé (with the beangenerator plugin)

19 Registering language and ontology instance Registering the defined ontology and the selected content language to the agent // register the SL0 content language getcontentmanager().registerlanguage(new SLCodec(), FIPANames.ContentLanguage.FIPA_SL0); Creating and handling content expression as Java objects that are instances of the classes developed in step 2 and let JADE translate these Java objects to/from strings or sequences of bytes that fit the content slot of ACLMessages // register the mobility ontology getcontentmanager().registerontology(mobilityontology.getinstance());

20 Creating request to AMS private ACLMessage preparerequesttoams(aid agent) { ACLMessage request = new ACLMessage(ACLMessage.REQUEST); request.addreceiver(getams()); request.setlanguage(fipanames.contentlanguage.fipa_sl0); request.setontology(mobilityontology.name); request.setprotocol(fipanames.interactionprotocol.fipa_request); // creates the content of the ACLMessage Action act = new Action(); act.setactor(getams()); WhereIsAgentAction action = new WhereIsAgentAction(); action.setagentidentifier(agent); act.setaction(action); public class WhereIsAgentAction implements AgentAction { private AID agentname; public WhereIsAgentAction() {} public void setagentidentifier(aid id) { agentname = id; } public AID getagentidentifier() { return agentname; } try { getcontentmanager().fillcontent(request, (REQUEST act); } catch (CodecException ignore) { :sender (agent-identifier :name da1@zadig:1099/jade) } catch (OntologyException ignore) {} :receiver (set (agent-identifier :name ams@zadig:1099/jade)) :content (( action return request; (agent-identifier :name ams@zadig:1099/jade) } (where-is-agent (agent-identifier :name Peter@Zadig:1099/JADE)) )) :language FIPA-SL0 :ontology JADE-Agent-Management :protocol fipa-request)

21 Parsing answer from AMS (INFORM :sender (agent-identifier :name :receiver (set (agent-identifier :name :content ((result (action (agent-identifier :name (where-is-agent (agent-identifier :name ) (set (location :name Container-1 :protocol JADE-IPMT :address Zadig:1099/JADE.Container-1 )) )) :reply-with :language FIPA-SL0 :ontology JADE-Agent-Management :protocol fipa-request ) private Location parseamsresponse(aclmessage response) { Result results = null; try { results = (Result)getContentManager().extractContent(response); } catch (UngroundedException e) { } catch (CodecException e) { } catch (OntologyException e) {} Iterator it = results.getitems().iterator(); Location loc = null; if (it.hasnext()) loc = (Location) it.next(); return loc; }

22 Lectures and others... MyHomepage/www/Lectures Login: agents Password: sawz2016

23 Interaction protocol FIPA defined IPs are: FIPARequest FIPAQuery FIPARequestWhen FIPAContractNet FIPAIteratedContractNet FIPAAuctionEnglish FIPAAuctionDutch FIPABrokering FIPARecruiting FIPASubscribe FIPAPropose

24 JADE-PROTO package The jade.proto package contains behaviours for both the Initiator and Responder role in the most common interaction protocols: FIPA-Request (AchieveREInitiator/Responder) FIPA-Contract-Net (ContractNetInitiator/Responder) FIPA-Subscribe (SubscriptionInitiator/Responder) FIPA-Propose (ProposeInitiator/Responder) All these classes automatically handle the flow of messages checking that it is compliant to the protocol the timeouts (if any) They provide callback methods that should be redefined to take the necessary actions when e.g. a message is received or a timeout expires

25 FIPA CFP

26 CFP communication schema

27 Initiation of CFP ACLMessage initiation = new ACLMessage(ACLMessage.PROPOSE); AID woman = new AID((String) getarguments()[0], AID.ISLOCALNAME); initiation.addreceiver(woman); initiation.setcontent("may I buy you a car?"); addbehaviour(new ProposeInitiator(this, initiation) { }

28 Step by step

29 Handle messages in protected void handleacceptproposal(aclmessage accept_proposal) { //your code protected void handlenotunderstood(aclmessage notunderstood) { //your code protected void handlerejectproposal(aclmessage reject_proposal) { //your code }

30 throw new NotUnderstoodException("I don't understand you");... } Other side (Participant(s)) addbehaviour(new ProposeResponder(this, mt) protected ACLMessage prepareresponse(aclmessage propose) throws NotUnderstoodException, RefuseException {... ACLMessage accept = propose.createreply(); accept.setperformative(aclmessage.accept_proposal); accept.setcontent(...);... ACLMessage reject = propose.createreply(); reject.setperformative(aclmessage.reject_proposal); reject.setcontent(...);... throw new RefuseException(...);...

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