ps4: meaning of abstract type "user"?

In ps4, the table table km_metadata_elements has these two
attributes

abstract_data_type varchar(30) not null, -- ie. "text" or
"shorttext" "boolean" "user"

-- this one is not null except when abstract_data_type is "user"

oracle_data_type varchar(30), -- "varchar(4000)"

(1) Does the abstract type "user" refer to the (acs) user table?

(2) Why the null when it's a user?

Or, does this have something to do with user-defined objects in
Oracle?

-- Bill Campbell, April 28, 2000

Answers

to define what are the steps?

-- Ella Cecilia Remando, September 1, 2005