The ratings on Goodlettsville, Tenn.-based Dollar General Corp. are based on its good business position, partially offset by concerns about financial and operating controls associated with an aggressive expansion program and an ongoing SEC investigation. Dollar General has a track record of mid-to-high single-digit same-store sales and a niche position in small town markets serving the "extreme value" segment of the discount industry. Its base of about 6,500 small-format stores provides inexpensive consumable basics to low- and fixed-income families. However, the stores are increasingly facing competition from large-format discounters and other "dollar" retailers. This pressure increases the importance for Dollar General to successfully execute its in-store performance. Store-level execution has been inconsistent despite good historical same-store sales, in large part