I'm trying to import excel files into pet table. The pet table contains a pet_owner field. GUID is hard to retrieve, I don't want to use GUID, I want to use alternate keys. Can I use Web API style addressing method to uniquely identity a pet_owner, perhaps looks like pet_owners(external_id='U001') ?

I have tried but failed, the error message is 'The lookup reference could not be resolved.'

Background:
I have two tables: pet_owner and pet. Pet table has a pet_ownerid field.
Pet table has an alternate key with only one column: external_id.
Pet_owner table has an alternate key with only one column: external_id.