Discovery

Basically, the Directory Facilitator agent (DF) is a yellow pages server. Provider agents may register (and deregister) the types of services they perform with the DF. Client agents may search the DF for providers of a given service.

The interface to the DF agent is through the DFService utility class. We also provide a DFUtils class.

ProviderAgent.java

Our provider agent has a single provider behavior that performs two distinct services called "ServiceA" and "ServiceB":

class ProviderBehavior extends CyclicBehaviour {

protected ACLMessage makeReply(ACLMessage msg) {
String info = msg.getContent();
ACLMessage reply = msg.createReply();
if (info.equals("ServiceA")) {
reply.setContent("Performing serviceA for " +
msg.getSender().getLocalName());
} else if (info.equals("ServiceB")) {
reply.setContent("Performing serviceB for " +
msg.getSender().getLocalName());
} else {
reply.setContent("What?");
}
return reply;
}

public ProviderBehavior(Agent a) { super(a); }

public void action() {
ACLMessage msg = myAgent.receive();
if (msg != null) myAgent.send(makeReply(msg));
block();
}
}

Of course we could have created two separate behaviors, one for each service.

During setup, the provider agent creates a DFD (DFAgent description record). The DFD will contain the AID of the agent plus information about the protocols, ontologies, languages, and services the agent supports:

DFAgentDescription dfd = new DFAgentDescription();
dfd.setName(getAID());

For each service the agent performs, we must create a service description and add it to the DFD. For example:

ServiceDescription serviceA = new ServiceDescription();
serviceA.setType( "serviceA" );
serviceA.setName( getLocalName() );

Before registering the DFD, we must deregister previous incarnations:

DFAgentDescription list[] = DFService.search( this, dfd );
if ( list.length > 0 ) DFService.deregister(this);

Now we are ready to register the DFD:

DFService.register(this, dfd);

During takedown the provider agent must deregister itself:

DFService.deregister(this);

Here's the complete code:

public class ProviderAgent extends Agent {

protected void setup() {

DFAgentDescription dfd = new DFAgentDescription();
dfd.setName(getAID());

ServiceDescription serviceA = new ServiceDescription();
serviceA.setType( "serviceA" );
serviceA.setName( getLocalName() );

ServiceDescription serviceB = new ServiceDescription();
serviceB.setType( "serviceB" );
serviceB.setName( getLocalName() );

try {
DFAgentDescription list[] = DFService.search( this, dfd );
if ( list.length > 0 ) DFService.deregister(this);
dfd.addServices(serviceA);
dfd.addServices(serviceB);
DFService.register(this, dfd);
} catch (FIPAException fe) {
System.err.println(fe.getMessage());
}

addBehaviour(new demos.ProviderBehavior(this));
System.out.println("Agent " + getLocalName() + " is ready!");
}

protected void takeDown() {
try {
DFService.deregister(this);
} catch (FIPAException fe) {
System.err.println(fe.getMessage());
}
System.out.println("Agent " + getLocalName() +
" is shutting down");
}
}

RequestAgent.java

Our request agent has two behaviors, one that sends a "ServiceA" request to all agents that provide ServiceA, and another that sends a "ServiceB" request to all agents that provide ServiceB. The RequestB behavior searches the DF for all agents that provide "ServiceB":

AID[] providers = DFUtils.searchDF(myAgent, "ServiceB");

To send a request for "ServiceB" to provider i is simple:

ACLMessage msg = new ACLMessage(ACLMessage.REQUEST);
msg.setContent( "ServiceB" );
msg.addReceiver( providers[i]);
myAgent.send(msg);

Here's the complete code:

class RequestBBehavior extends OneShotBehaviour {
public RequestBBehavior(Agent a) { super(a); }
public void action() {
AID[] providers = DFUtils.searchDF(myAgent, "ServiceB");
if (providers != null) {
for(int i = 0; i < providers.length; i++) {
ACLMessage msg = new ACLMessage(ACLMessage.REQUEST);
msg.setContent( "ServiceB" );
msg.addReceiver( providers[i]);
myAgent.send(msg);
msg= myAgent.blockingReceive();
if (msg!=null)
System.out.print("Response: " + msg.getContent());
System.out.println(" from " +
msg.getSender().getLocalName() );
} // for
} // if
}
}

Here's the code for the request agent:

public class RequestAgent extends Agent {

protected void setup() {
addBehaviour(new demos.RequestABehavior(this));
addBehaviour(new demos.RequestBBehavior(this));
}
}

DFUtils.java

public class DFUtils {
static void register( Agent a, ServiceDescription sd) { ... }
static AID getService( Agent a, String service ) { ... }
static AID [] searchDF( Agent a, String service ) { ... }
}

Single Service Registration

static void register( Agent a, ServiceDescription sd) {
DFAgentDescription dfd = new DFAgentDescription();
dfd.setName(a.getAID());

try {
DFAgentDescription list[] = DFService.search( a, dfd );
if ( list.length>0 )
DFService.deregister(a);

dfd.addServices(sd);
DFService.register(a, dfd);
}
catch (FIPAException fe) {
fe.printStackTrace();
}
}

Search for a single provider of a service

static AID getService( Agent a, String service ) {
DFAgentDescription dfd = new DFAgentDescription();
ServiceDescription sd = new ServiceDescription();
sd.setType( service );
dfd.addServices(sd);
try
{
DFAgentDescription[] result = DFService.search(a, dfd);
if (result.length>0)
return result[0].getName() ;
}
catch (FIPAException fe) {
fe.printStackTrace();
}
return null;
}

Search for all providers of a service

static AID [] searchDF( Agent a, String service ) {
DFAgentDescription dfd = new DFAgentDescription();
ServiceDescription sd = new ServiceDescription();
sd.setType( service );
dfd.addServices(sd);

SearchConstraints ALL = new SearchConstraints();
ALL.setMaxResults(new Long(-1));

try
{
DFAgentDescription[] result = DFService.search(a, dfd, ALL);
AID[] agents = new AID[result.length];
for (int i=0; i<result.length; i++)
agents[i] = result[i].getName() ;
return agents;

}
catch (FIPAException fe) { fe.printStackTrace(); }

return null;
}

Program output

In this example larry, curly, and moe are provider agents and abbot is a request agent:

Agent larry is ready!
Agent curly is ready!
Agent moe is ready!
Response: Performing serviceA for abbot from moe
Response: Performing serviceA for abbot from curly
Response: Performing serviceA for abbot from larry
Response: Performing serviceB for abbot from moe
Response: Performing serviceB for abbot from curly
Response: Performing serviceB for abbot from larry

Adding containers

We can start new containers in separate console windows using the command:

runjade -container

To start a container on a separate machine, we must specify the URL of the main container:

runjade -container -host myServer.cs.sjsu.edu

Of course once the container has started, it appears in the GUI and we can add agents to it:

Alternatively, we can add the agent at the command line:

runjade -container -host myServer.cs.sjsu.edu sue:demos.RequestAgent