Add search by attribute value, especially for person

Raxa needs to be able to search persons by attribute value, although we should define this in a way that works with other attribute types. I see 2 ways of doing this – one as a search on person, the other as a search on person_attribute_type. In both cases there would be a parameter with the uuid/name of the attribute ("attr=" for person, "q=" for person_attribute_type); and a "value=" parameter which would specify the value of the attribute being sought (and if missing, the result would include all persons with the attribute regardless of value). In the case of person, the result would be a list of persons. In the case of person_attribute_type, this would mean changing the full representation to include a "persons" collection which for each attribute would include all persons with that attribute, and in the case of the search, would be limited to those with the specified value. I would prefer to see this as a search on person.

I am unsure as to how to specify the value. In the case of text attributes, it seems easy. In the case of concept- or other table-based attributes, should it be the ID or the UUID? What if it's an external table-based attribute? What if it's a filepath value, do we return the filepath or the file? Right now, person_attribute returns the value field as text.