private void applyRanking(ImmutableSDField field, Attribute attribute) {
        Ranking ranking = field.getRanking();
        if (ranking != null && ranking.isFilter()) {
            attribute.setEnableOnlyBitVector(true);
        }
    }
Derives one attribute. TODO: Support non-default named attributes
config-model/src/main/java/com/yahoo/schema/derived/AttributeFields.java