FieldType for a field defined with no type in the ds.xml?

If I have a field defined in a ds.xml file without the type attribute, what FieldType is it associated to?

I am just trying to restrict Operators for field types via the call to setTypeOperators and I am not sure what FieldType to use.

Also, is there a way to set a default set of Operators regardless of the FieldType?

Thanks.