Thanks for reply, this doubt is in general for "link tables",actually im work in this.
the relationship is (role)1..N to 0..1(groups)
I want to make role groups, as you ask.
Imagine this Roles (adminA,adminB,Teachers) belongs to "Administrative" group.
Rol (teachers, adminB) belongs to "Evaluate student" group, and continuous for numerous combinations
The main idea is to create groups to contain roles, and give permissions to that groups to access some activities (one activitie has permission to some grouped pages), and not doing this role by role in a level role-page.
My doubt isn't necesary only to solve this example, I want to know what is the correct way to do, because I have more link tables in my database, and I use the first form in example (PK surrogate, fk, fk).
Thanks in advance Paul (sry my bad english)