Frequently Asked Questions
Why do I need to give you my email
If you requested an evaluation copy of JACK®
your email address is required for us to send you
a password to enable you to install JACK® and use it for the
of your evaluation period. We do not use any information provided
by you for any other external purpose and any information provided by
is treated with the utmost confidence.
didn't get my password sent to me? Why?
There are three possible reasons for this.
Check to ensure one of these reasons is not the cause first before
- You may have accidently mistyped your email address
- Your SPAM filter may have thought the email was SPAM and has
- 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.
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
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®
Do you provide any
using the JACK® Development Environment?
Yes. Look under the Help menu.
Do you provide any documentation?
documentation is provided as part of the JACK® Documentation
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
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
My Windows computer tells me that "Registry key
has value xxx, but yyy is required". What should I do?
This is a Java installation problem rather than a JACK® one
It sounds like your old Java xxx
runtime or JDK has become stuck in the registry. Possibly the previous
that was installed did not get uninstalled properly and now there are
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.
folder if it exists and the JDK folder, wherever you installed it)
- Search the registry for any key or value containing "java" and
it! (Use the "Run..." command and type 'regedit', then use
find command within regedit)
- Install the new JDK again.
- Make sure you have PATH & CLASSPATH set properly. Check that
"BIN" directory of the JDK is in your PATH since the Java installer
seem to do this for you.
The JACK® Compiler tells me " ** couldn't execute **". What
The JACK® compiler needs to be able to locate your java compiler, javac. The message indicates that
java compiler can't be found. You need to have installed a JDK (Java
Kit) and you need to add the bin
directory of wherever your JDK is installed to the PATH environment variable.
the Java installer may not do this for you. Under Windows 2000/XP, you
this from the Control Panel, under System, in the Environment tab.
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
If found, it should complain about being called without any java file
If it is not found, then there is still a problem. You may need to log
or reboot after setting the PATH
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
to complete (about half a second). It usually means that something is
out to Java code and not coming back, normally a bug with your code.
plan steps must execute quickly. In any case, the JACK® kernel
thread alone since it is taking too long and starts a new one to handle
plans. If the original one ever comes back then all is ok. If not, then
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
should the need arise. One quite flexible way is to use an Action
(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
infinite loop. Otherwise, there may be nothing to do because JACK®
waiting around for an event to process. There are tracing options
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
for an event to process. If you want the application to exit, you
call System.exit(0) explicitly
required. However, calling System.exit in this way stops everything
immediately. If JACK® was still processing, you may get unexpected
How are plans scheduled and how many threads does JACK® use
Within a single JVM, all JACK® agents are (normally) executed by
thread. JACK® includes a time based scheduler, which ensures
agents get a slice of execution. On top of that, each JACK® agent
many tasks pending at the same time so each agent can specify its own
manager. This provides the task execution
policy for that agent. The default is for the agent to stay committed
a task as long as possible.
Each JACK® plan is transformed by the compiler into steps in a
machine which can be executed by an agent's task manager. The executing
may leave the plan (task) and come back to it later, and then continue
the plan (task) later.
Thus, JACK® has only one thread. Plus an additional one for
In many applications, the code within an agent is "java interface
may be invoked by threads other than the JACK® scheduling thread.
receiving thread is an example of such a thread).
I get strange compilation errors but if I clean up first everything
ok. Why is that?
Some versions of the JACK® compiler had trouble telling apart Java
were automatically generated by JACK® from user provided Java
lead to many name clashes due to duplicate declarations. Newer versions
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
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
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
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
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
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
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
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
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
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
Copyright (C) 1997-2008, Agent
US Government Restricted Rights
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