# ARQ - Logging

ARQ uses Apache Commons Logging as the API and ships with Log4J as a deployment system. You can use Java 1.4 logging instead.

ARQ does not output any logging messages at level INFO in normal operation. The code uses level TRACE and DEBUG. Running with logging set to an application at INFO will cause no output in normal operation. Output below INFO can be very verbose and is intended mainly to help debug ARQ. WARN and FATAL messages are only used when something is wrong.

The root of all the loggers is "com.hp.hpl.jena". "com.hp.hpl.jena.query" is the application API. "com.hp.hpl.jena.sparql" is the implementation and extensions points.

If using in Tomcat, or other system that provides complex class loading arrangements, be careful about loading from jars in both the web application and the system directories as this can cause separate logging systems to be created (this may not matter).

ARQ Documentation Page