The cart/order service is used to maintain the cart operation and deals with the deletion or addition of items, in much the same way that the categories and cataloger service is used to show the available categories and the different products under those categories, as well as their catalogs. The offers service is used to store offer-related information, such as which offer is live, and in which geolocation. The offers service can have a validation service as well. For instance, it can validate whether one offer should be used twice on the cart, or if the offer that the user applied is still live or not, or applicable to a certain category, and so on. There could be many, many different combinations of these offers and their validity, so the developer could think of having the validation service as separate from the offer service. But, for now, this is not required in our example.