American Eagle is considered a "Service Partner", not an Airlink.
Airlink's are painted with an NW colorscheme. Service Partners operate as an independent carrier which codeshare with NW.
Airlinks are: Mesaba, Express Airlines I, Pacific Island Aviation.
Service Partners include: AS, QX, AZ, KQ, GQ, American Eagle, Business Express, Gulfstream.
Continental and KLM are Alliance Partners, because the agreements with them go beyond mere codesharing.