public void addIndex(ParsedIndex index) {
        String idxName = index.name();
        verifyThat(! fieldIndexes.containsKey(idxName), "already has index", idxName);
        fieldIndexes.put(idxName, index);
    }
get an existing summary field for modification, or create it
config-model/src/main/java/com/yahoo/schema/parser/ParsedField.java