Should GET requests to realtionship urls only return type and id?

Hi, just want to make sure I am understanding the specification correctly.

Groups have many Users.

I have a url in my app

A GET request to that URL returns

  [{"id"=>"6", "type"=>"user"},
   {"id"=>"5", "type"=>"user"},
   {"id"=>"4", "type"=>"user"},
   {"id"=>"3", "type"=>"user"},
   {"id"=>"2", "type"=>"user"},
   {"id"=>"1", "type"=>"user"}],
 "links"=>{"self"=>"/api/v1/groups/1/relationships/users", "related"=>"/api/v1/groups/1/users"}}

Is this the correct approach?

My understanding is that relationship objects should always be limited to type/id ? Where an included object would contain actual resources (more attributes basically)?

Any help clarifying this would be great! Thanks.