It depends a bit on your data access technology, but it's common to take the user's name / identity into account as well as the role membership. In pseudo code the following LINQ query would accomplish this:
bool userIsAdministrator = User.IsInRole("Administrators");
var whatever = from a in Articles
where a.CreatedBy == User.Identity.Name || userIsAdministrator
This selects all articles that belong to a user, or really al articles when the user is an admin.
You can do similar stuff for direct SQL or other database access methods.
Hope this helps,