Composite types or composite keys?

Hi,

I was reading about composite types and wondering if I should use them instead of composite keys. I currently have tables like this:

create table products (
source_system text,
product_id text,
description text,
...
primary key (source_system, product_id)
);
create table inventory (
source_system text,
product_id text,
qty int,
...
foreign key (source_system, product_id) references products
);

and it means having to add the “source_system" column to many queries. Would something like:

create type product as (
source_system text,
product_id text
);
create table products (
product product,
description text,
...
primary key(product)
);
create table inventory (
product product,
qty numeric,
...
foreign key (product) references products
);

be a correct use of composite types? I rarely need to see the columns separately, so having to write “(product).product_id” won’t happen much in practice.

Thanks,

Tony