This approach is akin to (and in fact generalizes) the common method of studying a ring by investigating the modules over that ring. The ring takes the place of the category , and the category of modules over the ring is a category of functors defined on .
This approach is akin to (and in fact generalizes) the common method of studying a ring by investigating the modules over that ring The ring takes the place of the cat.egory , and the category of modules over the ring is a category of functors defined on .