Allow custom key type in argument and result maps

[vruusmann]

The Evaluator#evaluate(Map) method requires argument and result maps to be keyed using org.dmg.pmml.FieldName type:

Map<FieldName, ?> arguments = ...;
Map<FieldName, ?> results = evaluator.evaluate(arguments);

Most applications employ some other key type (typically java.lang.String) in their data schemas, which necessitates explicit custom key -> org.dmg.pmml.FieldName -> custom key translation.

The explicit key translation could be avoided if the org.jpmml.evaluator.Evaluator interface was generified:

public interface Evaluator <InKey, OutKey> {
  Map<OutKey, ?> evaluate(Map<InKey, ?>);
}

The translation between application-specific key types and the org.dmg.pmml.FieldName type would be handled by configuring appropriate org.jpmml.evaluator.InputMapper and org.jpmml.evaluator.ResultMapper instances.

This is a breaking change, to be implemented in the beginning of the 1.5.X development series.

[vruusmann]

Was addressed in the 1.6.X development branch by changing the key type of argument and result maps from org.dmg.pmml.FieldName to java.lang.String.

String-keyed maps should be much easier to interface with application-specific data records.