Finding items you want can be difficult because of the number of items for sale. You can return too many items in a response or return no items at all. Amazon addresses this difficulty by placing every item it sells into a product category, called a search index.
Search indices can be divided in groups of everything for sale on Amazon, as shown in the following example:
By specifying one slice in a request, you avoid returning items in all the other slices. This makes requests more targeted and reduces search times. For example, when looking for a specific book, specify the Books search index in the request.
Titles and keywords used to find items often occur in multiple search indices. For example, if you search for "Harry%20Potter" as your keyword, the Product Advertising API can return results in many search indices, including Books, DVD, Video, and Music. By specifying the search index, your request is better targeted.
Specifying the wrong search index leads to no results or results that don't meet customer search criteria. For example, if your keyword is "carburetor" and the search index is Kitchen, the Product Advertising API might not return items that match the search criteria. However, change the search index to Automotive and you get better results.