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The core feature is necessary, because it contains all fundamental functions for Odysseus.
See Adding features to products how to add a new Feature to an existing product.
Logging
Odysseus comes with the Simple Logging Facade for Java (SLF4J). To use logging add the de.uniol.inf.is.odysseus.slf4j bundle. In this bundle you can find the log4j.properties to configure the logging behaviour.