private boolean isAccessingDiskSummary(String source) {
        SDField field = getConcreteField(source);
        if (field == null) return false;
        if (field.doesSummarying() && !field.doesAttributing()) return true;
        return false;
    }
Returns the first occurrence of an attribute having this name, or null if none
config-model/src/main/java/com/yahoo/schema/Schema.java