Complex sentence: Nevertheless, World's Biggest Bookstore still claims the title on the basis that it depends on how "biggest" is defined: while Barnes and Noble has more floor space, World's Biggest Bookstore carries more titles.
Split into simpler sentences: Nevertheless, World's Biggest Bookstore still claims the title on the basis that it depends on how "biggest" is defined. The Barnes and Noble has more floor space, although World's Biggest Bookstore carries more titles.