The xvalidation package contains all classes for a cross validation flow. The workflow between the {@link org.knime.base.node.meta.xvalidation.XValidatePartitionModel} node and the {@link org.knime.base.node.meta.xvalidation.AggregateOutputNodeModel} node should consist of at least a learner and its predictor. The output of the predictor should be connected to the aggregator node. The class column set in the aggregator node and the predictor has to be the same.