NetKernel News Volume 1 Issue 6

November 27th 2010

What's new this week?

• Ongoing refinements to core modules
• Some new features for DPML
• rdf-jena updated
• JMS transport makes a showing.

All the following updates can be installed through Apposite on a standard NKSE 4.0.1 installation. Go to Apposite Admin -> Synchronize and then select "Update" on the orange highlighted packages. (Yes we know its a pain that there's no "install-all-updates" option - we will add this soon!).

System Updates

Standard Module has been through a further round of review. Some robustness enhancements have been made for the commission/recommission cycle. In particular, if a low-level java.lang.Error is thrown, for example if a ClassDef is not found or there is JVM class versioning mismatch. The Standard Module now gracefully handles these low-level JVM issues and provides broken module reports viewable in the Space Explorer.

A corollary to the Standard Module update is that the Module Manager is now able to detect removal of all modules even if they are broken. Previously this required a full restart.

While looking at Java-level error handling we fixed the exception stack trace to limit the stack depth size of general Java Exceptions to the value specified in the kernel settings. Previously only the NKFExceptions were managed by this setting. This change makes deep stack traces much less cluttered and readable. (as ever you can set the value dynamically in the kernel setting control panel if the vital details are not showing for a bug you're tracking down).

The cron module's logging has been enhanced, and through much gnashing of teeth at the intransigence of Log4J, has been persuaded to issue its logs to the NetKernel log infrastructure and so can be viewed with the log viewer. One consequence of this - if/when you install the cron update, afterwards you should go to the log-level management tool and turn off Fine, Finer, Debug http://localhost:1060/tools/log-levels (otherwise you will see log messages every 5 seconds from the cron job that detects new cron jobs!).

The NO_CACHE response header (which indicates that a representation should not be cached itself, but which does not prevent higher order composite resources from being marked cacheable and/or depending on it) was previously not something that could be overridden when relaying a response (for example in a DPML process). This restriction has been removed and NO_CACHE can now be overridden (DPML users can use the modify-response tag for this).

DPML gains a new "log" tag - which provides comprehensive access to the logging infrastructure and puts DPML on parity with procedural NKF logging. Details are documented in the DPML reference book.

Repository News

rdf-jena library has been updated to use the latest Jena 2.6.2 library. This update was prompted by some ongoing development work to create an OWL ontology resource model based on Pellet 2.0 - anyone interested in an early release copy of this let us know.

jms-transport: a JMS transport library is now available. Similar to the design of the JMS transport on NK3, it provides a Transport that can listen to topics/queues and when received will issue a ROC request into its hosted space with the message. An accessor provides client/server symmetry and enables messages to be initiated to topics/queues.

The jms-transport includes detailed documentation on how to use the services out of the box and customization notes if you need to adapt the implementation for a specific JMS vendor's proprietary headers etc.

Also provided is a step-by-step tutorial showing how to set up and use the jms-transport. It uses Apache Active MQ as the reference JMS tool. The tutorial shows how to create an ESB-like message relay, where a REST/HTTP POST message is received and reissued to JMS topic, in 5 lines of code.

ROC News

Our American friends will know its been the Thanksgiving holiday. One more thing to be grateful for, is that Tony didn't have time to blog this week.

Enjoy the weekend!