Wiki code for Frequently Asked Questions

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1: 1 Frequently Asked Questions (FAQ)
2: 
3: *How can I create and start a Jadex agent on a JADE apapter platform (e.g. jadex-jadeadapter-0.96) by programming in an external application?*
4: 
5: To start a Jadex agent from an external application you can follow the instructions of the JADE programmers guide on how to create a new agent container and then execute the following code:
6: 
7: {code}
8: jade.wrapper.AgentContainer container;
9: ...
10: String name = "myagent"; // Any string can be used as agent name.
11: String model = "jadex.examples.helloworld.HelloWorld";    // Logical or XML file names can be used to identify the agent model.
12: String config = "default";    // The configuration to be used.
13: String clazz = "jadex.adapter.jade.JadeAgentAdapter";    // JADE adapter class. Do not change this.
14: 
15: Object[] args = new Object[]{model, config}; // Custom args may be included after the config (as "name=value" pairs).
16: jade.wrapper.AgentController ac = container.createNewAgent(name, clazz, args);
17: ac.start();
18: {code}
19: 
20: 
21: *On the platform of jadex-jadeadapter-0.96, when I start a Jadex agent, whose model (XML file) includes an predefined capability of jadex-0.96, e.g. with the statement "<capability name=’procap’ file=’jadex.planlib.Protocols’/>", it will show the message "can’t load capability file ’ jadex.planlib.Protocols’ on the console . Why? How can I start this kind of Jadex agent?*
22: 
23: Please post this question in the forum and provide more details. It could be a classpath issue or something else.
24: 
25: 
26: *When I start the Jadex platform 0.96 (or older) together with the JADE adapter I get a strange error (e.g. ClassCastException) and the JADE RMA does not show up. What can be the reason for that?*
27: 
28: In Jadex 0.96 and earlier, you should set-up cleanly separated environments for running Jadex with the Standalone resp. the JADE platform. For setting up a clean environment you should consider the following aspects:
29: 
30: * Both versions should not be started from the same directory, as both use the jadex.properties and overwrite values in it (or should explicitly use different propoerties). As the settings are incompatible this may cause troubles.
31: * Secondly, you should also separate classpath settings of both Jadex versions. It causes troubles if more than adapter jar is included as the wrong service classes might be used (AMS/DF etc).
32: 
33: 
34: *I start the Jadex platform with "java -jar jadex_standalone.jar" (or "java -jar jadex_jadeadapter.jar") and have added my own classes to the classpath. Nevertheless my classes are not found. Why?*
35: 
36: When you use the "-jar" option Java will ignore all classpath settings (see e.g. 
37: [Java docs>http://java.sun.com/j2se/1.4.2/docs/tooldocs/windows/java.html]) Therefore, add your required classes to the project in the starter panel or do not use the "-jar" option.
38: Typical stack trace is :
39: {code:none}
40: ***  Uncaught Exception for agent agentname  ***
41: java.lang.RuntimeException: Cannot start agent agentname due to errors in model:
42: Report for Agent(MyJadexAgent)
43: File: file:/MyJadexAgent.agent.xml
44: 
45: MPlanBody(expression = ):
46: Unknown type: MyPlan
47: 
48: at jadex.adapter.JadexAgentFactory.createJadexAgent(JadexAgentFactory.java:33)
49: at jadex.adapter.jade.JadeAgentAdapter.setup(JadeAgentAdapter.java:119)
50: at jade.core.Agent$ActiveLifeCycle.init(Unknown Source)
51: at jade.core.Agent.run(Unknown Source)
52: at java.lang.Thread.run(Thread.java:595)
53: ERROR: Agent agentname died without being properly terminated !!!
54: State was 2
55: {code}
56: 
57: 
58: *I get the message while loading an agent in the Jadex-RMA console: No model loaded: java.io.IOException Unable to access binding information for class jadex.model.jibiximpl.MBDIAgent*
59: 
60: Use developer version or run
61: 
62: org.jibx.binding.Compile -v kernel/src/jadex/model/jibximpl/binding.xml
63: 
64: 
65: *What does "retrydelay" flag mean?*
66: 
67: Without retrydelay goal processing works as follows: goal -> plan 1 -> plan 2 -> plan 3 -> ... until the goal is failed or succeeded.
68: The retrydelay just specifies a delay in milliseconds before trying the next plan, when the previous plan has finished, i.e.: goal -> plan 1 -> wait -> plan 2 -> wait -> plan 3 -> ... until goal fails or succeeds. This is e.g. useful, when already tried plans are not excluded from the applicable plan set, leading to the same plan being tried over and over again.
69: 
70: 
71: *How can the environment of a Jadex MAS be programmed?*
72: 
73: We tried out different approaches for realizing the environment of a MAS. In the most simple case we realized the environment as a singleton object for all agents. Of course this approach is limited in nature as it is not possible to distribute the application over more than one Java VM. In this case we used a simple belief with a fact expression that refers to that singleton object, e.g. you can look at the garbagecollector example in the ADF you can find:
74: {code:xml}
75: <!-- Environment object as singleton.-->
76: <belief name="env" class="Environment">
77:     <fact>Environment.getInstance($agent.getType(), agent.getName())</fact>
78: </belief>
79: {code}
80: 
81: If distribution is needed we used the approach of a separate environment agent. This agent administers the environment and permits several actions being executed on the environment object. Therefore a domain specific ontology is defined, in which the actions are contained together with the FIPA stuff (agent action, agent identifier etc.). In principle each agent has to create the specific action it wants to perform on the environment (such as moveup) and encode it into an AgentAction (see FIPA spec). The environment agent tries to execute the contained action and sends back the result e.g. Done(AgentAction). As this procedure is cumbersome, we used following idea. For every primitive action a goal is defined with corresponding plans that do the message handling. The agent programmer can subsequently use just the goals for interaction with the environment.
82: 
83: 
84: *I have change the .java file, e.g. a plan. Why are my changes not reflected in the running Jadex system?*
85: 
86: Jadex relies on the Java class loading mechanism. This means that normally Java classes are loaded only once into the VM. You need to restart the Platform for taking the changes effect. Since Jadex 0.94 a plan class reloading at runtime is also possible when the Jadex expression interpreter is used and the corresponding option "plan reloading" option is turned on in the Jadex settings. In contrast to plan classes XML changes inlcuding inline plan bodies (only available with the expression compiler add-on available from the [Jadex add-on page>Download.Add Ons]) are directly reflected whenever the model is laoded. The reason for this is that inline plan bodies can be compiled on demand at runtime.
87: 
88: 
89: *In my agents there is always one plan for a goal. Why do I need goals anyway?*
90: 
91: You don’t need to use goals for every problem. But, in our opinion using goals in many cases simplifies the development and allows for easier extensions of an application. The difference between plans and goals is fundamental. Goals represent the "what" is desired while plans are characterized by the "how" could things be accomplished. So if you e.g. use a goal "achieve happy programmers" you did not specify how you want to pursue this goals. One option might be the increase of salary, another might be to buy new TFT monitors. Genereally, the usefulness of goals depends on the concrete problem and its complexity at hand.
92: 
93: 
94: *How can the agent become aware of or react to its own death?*
95: 
96: Since version 0.96 Jadex supports not only initial states but also end states. Whenever an agent is terminated its execution will not be immediately stopped. Instead the agent changes its state to "terminating", aborts all running goals and plans and activates elements declared in the end state. For details please have a look at [Userguide, Chapter 13, "Configurations">http://vsis-www.informatik.uni-hamburg.de/projects/jadex/jadex-0.96x/userguide/index.single.html#configurations]. If you want to be notified when an agent dies you can use an agent listener (cf. [Userguide, Section 15.2, "Agent Listeners">http://vsis-www.informatik.uni-hamburg.de/projects/jadex/jadex-0.96x/userguide/index.single.html#externalinteractions.listeners]).
97: 
98: 
99: *How can I parametrize an agent and set parameter values before starting?*
100: 
101: Since Jadex 0.96 the way agent arguments are specified has changed. All agent beliefs that are "exported" are automatically considered as agent parameters. The JCC gui automatically creates input fields for these exported parameters. Programmatically, the arguments can be directly referenced via their associated beliefs.
102: 
103: 
104: *Is there some preferred persistence mechanism for beliefs?*
105: 
106: In the current version Jadex does not provide a ready-to-use persistence mechanism for the beliefs of an agent. We have successfully used normal object-relational mapping frameworks such as [Hibernate>http://www.hibernate.org/] in combination with Jadex. Nonetheless, the task of persisting data cannot be fully automated and needs to be done in plans. This topic should be an issue of further research and improvement.
107: 
108: 
109: *Can capabilities be used for group communication, i.e. are they some kind of tuple space, where one agent puts in data and other can read it?*
110: 
111: No, this seems to be a common misunderstanding of the concept. A capability is comparabale to a module. Each agent that includes a capability get a separate instance of that module. For details have a look at [Userguide, Chapter 5, "Capabilities">http://vsis-www.informatik.uni-hamburg.de/projects/jadex/jadex-0.96x/userguide/index.single.html#capabilities].
112: 
113: 
114: *When I call agent functionality from a user interface (or some other external application) I am getting an exception, what shall I do?*
115: 
116: Exception in thread awt-EventQueue-0 java.lang.RuntimeException wrong thread calling plan interface...
117: 
118: Concurrent access to the internals of an agent is not allowed by the Jadex kernel to avoid inconsistent states. Hence, Jadex ensures that only the agent thread (or its plans) can access the agent internals directly, other processes have to use external process interface. You can find a detailed explanation and a code example in the [Userguide, Chapter 15.1, "External Processes">http://vsis-www.informatik.uni-hamburg.de/projects/jadex/jadex-0.96x/userguide/index.single.html#externalinteractions.processes].
119: 
120: *How can i retrieve event information from body of some plan (getInitialEvent() in jadex 0.96 version) in jadex 2.0 ?*
121: 
122: The method getInitialEvent() has been replaced by the getReason() method. This has been done, because you can now also get information about other triggering reasons for executing a plan, such as belief changes. The method returns an IElement object, which can be casted to the object that you expect. E.g. for a plan triggered by a message event, you should do:\\
123: {code}
124: IMessageEvent messageevent = (IMessageEvent)getReason();
125: {code}
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