JACK® Frequently Asked Questions

Why do I need to give you my email address?

If you requested an evaluation copy of JACK® then your email address is required for us to send you a password to enable you to install JACK® and use it for the duration of your evaluation period. We do not use any information provided by you for any other external purpose and any information provided by you is treated with the utmost confidence.

I didn't get my password sent to me? Why?

There are three possible reasons for this.

You may have accidently mistyped your email address
Your SPAM filter may have thought the email was SPAM and has withheld/deleted it.
Mail to/from Hotmail or Yahoo accounts sometimes get blocked along the way for reasons beyond our control. Avoid registering with free accounts if you are affected by this.

Check to ensure one of these reasons is not the cause first before contacting us.

Do I need Java on my computer?

Yes you need a Java Development kit or equivalent installed on your computer. A Java runtime by itself is not enough.

Do you provide any examples?

The JACK® installation comes complete with a set of examples. The examples are in the sub-directory examples. Or look under the Help menu in the JACK® Development Environment (JDE).

Do you provide any examples using the JACK® Development Environment?

Yes. Look under the Help menu.

Do you provide any documentation?

JACK® documentation is provided as part of the JACK® Documentation package. This package is separate from JACK® itself. Once installed, the documents (in PDF and HTML format) are in the doc subdirectory. You can access the JACK® documentation from the Help menu of the JDE. There should also be a link in the automatically installed menu or shortcuts - if not, point your browser at the file doc/jackdocs.html in the place where you installed JACK®and it will guide you to all the available documentation.

My Windows computer tells me that "Registry key 'Software\JavaSoft\Java Runtime Environment\CurrentVersion' has value xxx, but yyy is required". What should I do?

This is a Java installation problem rather than a JACK® one specifically. It sounds like your old Java xxx runtime or JDK has become stuck in the registry. Possibly the previous Java that was installed did not get uninstalled properly and now there are incompatible Java components mentioned in the registry.

Although tedious, we suggest the following.

Uninstall all Java or JDK software (via Control Panel).
Make sure all Java or JDK software are actually removed. (E.g. delete the C:\Software\JavaSoft folder if it exists and the JDK folder, wherever you installed it)
Search the registry for any key or value containing "java" and remove it! (Use the "Run..." command and type 'regedit', then use the find command within regedit)
Install the new JDK again.
Make sure you have PATH & CLASSPATH set properly. Check that the "BIN" directory of the JDK is in your PATH since the Java installer does not seem to do this for you.

The JACK® Compiler tells me " couldn't execute ". What does this mean?

The JACK® compiler needs to be able to locate your java compiler, javac. The message indicates that the java compiler can't be found. You need to have installed a JDK (Java Development Kit) and you need to add the bin directory of wherever your JDK is installed to the PATH environment variable. Unfortunately the Java installer may not do this for you. Under Windows 2000/XP, you can do this from the Control Panel, under System, in the Environment tab. Under Windows 95/98 etc. you would need to edit C:\AUTOEXEC.BAT.

To test this, open a Command Prompt window and type javac and see if the command is found. If found, it should complain about being called without any java file arguments. If it is not found, then there is still a problem. You may need to log out or reboot after setting the PATH variable.

One other potential problem is if your PATH environment variable has quotes in it. If so, the JDE may not be able to compile your programs. Edit the PATH as described above, and remove any quotes.

I get the message "New Executor spawned due to mis-behaving agent". What's going on?

This happens when any plan step of a reasoning method (e.g. body()) takes an unreasonably long time to complete (about half a second). It usually means that something is calling out to Java code and not coming back, normally a bug with your code. Individual plan steps must execute quickly. In any case, the JACK® kernel leaves that thread alone since it is taking too long and starts a new one to handle other plans. If the original one ever comes back then all is ok. If not, then the agent mentioned is hung.

Often this is harmless but it might indicate a bug in your code. There are several ways you can include a lengthy computation within a plan step should the need arise. One quite flexible way is to use an Action cursor (aos.jack.util.cursor.Action). See the JACK® User Guide for details.

My JACK® program just hangs and does nothing.

If the process is using a lot of CPU, then you may simply be stuck in an infinite loop. Otherwise, there may be nothing to do because JACK® is just waiting around for an event to process. There are tracing options described in the JACK® User Guide which may be of use.

Why doesn't my JACK® program exit?

JACK® applications never exit on their own. The JACK® kernel is always waiting for an event to process. If you want the application to exit, you should call System.exit(0) explicitly when required. However, calling System.exit in this way stops everything immediately. If JACK® was still processing, you may get unexpected results.

How are plans scheduled and how many threads does JACK® use itself?

Within a single JVM, all JACK® agents are (normally) executed by just one thread. JACK® includes a time based scheduler, which ensures that all agents get a slice of execution. On top of that, each JACK® agent can have many tasks pending at the same time so each agent can specify its own task manager. This provides the task execution
policy for that agent. The default is for the agent to stay committed to a task as long as possible.

Each JACK® plan is transformed by the compiler into steps in a finite state machine which can be executed by an agent's task manager. The executing thread may leave the plan (task) and come back to it later, and then continue progressing the plan (task) later.

Thus, JACK® has only one thread. Plus an additional one for receiving messages.

In many applications, the code within an agent is "java interface code", which may be invoked by threads other than the JACK® scheduling thread. (The message receiving thread is an example of such a thread).

I get strange compilation errors but if I clean up first everything is ok. Why is that?

Some versions of the JACK® compiler had trouble telling apart Java files that were automatically generated by JACK® from user provided Java files. This lead to many name clashes due to duplicate declarations. Newer versions of the compiler should be ok but if in doubt, clean it out!

What is BDI?

The Belief-Desire-Intention (BDI) agent model is an event-driven execution model providing both reactive and proactive behavior. The BDI agent model is built on a simplified view of human intelligence. In it, agents have a view of the world (Beliefs), certain goals they wish to achieve (Desires), and they form Plans (Intentions) to act on these using their accumulated experience. Agents that are written using the BDI model are at a level of abstraction closer to normal human experience..

What are "Capabilities"?

JACK® supports code reuse through the "Capability" concept.

JACK® Version 1.3 introduced Capabilities to address the issues of modularisation and code reuse in the context of the agent modelling. A JACK® capability represents a cluster of functional components to be used as building blocks during the development of BDI agents. As a design concept they assist in the structuring of agent functionality into meaningful units. At the code level they reduce the amount of source code required when Capabilities are used across different types of agents. Capabilities also support the building of agent code libraries that can be plugged in to new developments.

How do I integrate JACK® agents with legacy applications?

JACK® agents are built as components within an application and allow seamless connection with legacy software. JACK® agents are accessible in Java code as normal Java objects, enabling agents' reasoning to be integrated with the processing of legacy applications.

JACK® also includes support for inter-process data transport between Java and C++ processes (using JACOB). JACK® may also be used with the Java Native Interface (JNI) to inter-link C++ and Java code within a single process.

What reasoning models does JACK® support?

JACK® has a modular design incorporating a generic inference engine that can be tailored by means of plug-in code modules. The default agent model provided is the BDI agent model, which is aimed at "practical reasoning", i.e. reasoning for action. The BDI inference engine implements the procedural reasoning principle of processing plans to fulfill goals.

JACK® also provides a Teams reasoning model.

What communication protocols does JACK® use?

The JACK® package includes a standard communications layer that uses UDP/IP based messaging with a reliability layer. While JACK® is delivered with a communications infrastructure of its own, an application may also use a pre-existing or other means of communications (such as CORBA, RMI, etc.).

JACK® agent messages are declared in a similar way to Java classes and end up being Java objects to be sent and received. These objects are then streamed using Java serialization, or by using the companion package JACOB, for improved messaging performance and flexibility (the JACOB binary format is up to ten times faster than Java serialization).

At the programming level, JACK® agents interact via "send" and "reply" primitives. These support multi-casting; that is, the same message may be sent to several recipients and an agent may wait for the replies in a resource free manner. Higher level communications protocols are implemented as "capabilities" that are reusable among agents.

How do I write distributed agent applications in JACK?

JACK® agents communicate via peer to peer messaging. Messages are sent to a named agent at a named portal, and it is unimportant to the sending agent whether the receiver is in the same process or in a different process. JACK® agents are therefore easily distributed to multiple processes and even multiple machines.

How efficient are JACK® agents?

JACK® agents are extremely efficient and light weight. This is demonstrated by having JACK® running on a handheld Psion 5mx.

Benchmarks using JACK® have shown the following:

Agents can be created at a rate of over 1,000 per second. An example program which times the creation of 100,000 agents reported 72,811ms total time running on a typical midrange PC under Linux.

Moreover, Agent destruction delay is insignificant. It is of the order of 10µ-s (ten microseconds) or 100,000 agents destroyed per second. An example program which times the destruction of 100,000 agents reported 329ms total time running on an average PC under Linux.

Agents can send messages to another agent within the same process in times of the order of 10µ-s (ten microseconds) or 100,000 messages per second. An example program which times the sending of 200,000 such messages reported 2662ms total time running on an average PC under Linux.

The JACK Modules and relevant Software Material have been developed entirely at private expense and are accordingly provided with RESTRICTED RIGHTS. Use, duplication, or disclosure by Government is subject to restrictions as set forth in subparagraph (c)(1)(ii) of DFARS 252.227-7013 or subparagraph (c)(1) and (2) of the Commercial Computer Software Restricted Rights and 48 CFR 52.2270-19, as applicable.