Overriding fields in types might not be the desired situation in some cases. Common field-names such as "name" or "description" are prone to be a subject of conflict. I have not investigated how important it might be to prevent this type of overriding. However, i came up with an idea to work-around it.

The following mockup is a speculation on how field-overriding might be prevented:

1     module @[subtype] {
2     
3         type mytype : supertype1 as one, supertype2 as two, supertype2 as twotwo {
4             id : Integer32 => AutoNumber();
5             field1 : Text#800;
6             one_field1 : Text#500;
7             two_field1 : Text#20;
8             twotwo_field1 : Text#20;
9         } where identity(id);
10         
11         mytypes : mytype*;
12         
13         type supertype1 { field1 : Text#500;}
14         
15         type supertype2 { field1 : Text#20;}
16     }

I found the smallest field has a priority; without renaming fields, there would just be 1 'field1'. And it would be 20 characters; instead of 500.