static String getSource(SummaryField summaryField, Schema schema) {
        if (summaryField.getTransform() == SummaryTransform.NONE) {
            return "";
        }

        if (summaryField.getTransform() == SummaryTransform.ATTRIBUTE ||
                (summaryField.getTransform() == SummaryTransform.ATTRIBUTECOMBINER && summaryField.hasExplicitSingleSource()) ||
                summaryField.getTransform() == SummaryTransform.COPY ||
                summaryField.getTransform() == SummaryTransform.DISTANCE ||
                summaryField.getTransform() == SummaryTransform.GEOPOS ||
                summaryField.getTransform() == SummaryTransform.POSITIONS ||
                summaryField.getTransform() == SummaryTransform.TOKENS ||
                summaryField.getTransform() == SummaryTransform.ATTRIBUTE_TOKENS)
        {
            return summaryField.getSingleSource();
        } else if (summaryField.getTransform().isDynamic()) {
            return DynamicSummaryTransformUtils.getSource(summaryField, schema);
        } else {
            return "";
        }
    }
Returns the command name of a transform
config-model/src/main/java/com/yahoo/schema/derived/SummaryClass.java