Amazon has a robust API and many Web Services which are open to the public. This means developers can take advantage of Amazon services directly from their own applications.
The AMS service is for Merchants who want to connect with Amazon’s main database and utilize the affiliate services. Merchants can add Amazon products directly on their own webSite and take a commission off the sales of those products.
Amazon also has services to connect to other products they offer such as their payment services, which are similar to PayPal in their integration. Also, some storage services and web statistics computing services. Along with the rest of their arsenal. All of these services are available via a standard merchant account.
They also have a service called AIMS. AIMS is their open API for their inventory and repricing data. Only merchants with a professional account can access this API. It uses something like XMLRPC or SOAP to manage calls to and from the Amazon server. This is close to getting real time inventory updates. This means a developer can utilize this API to create inventory updates from their own Database or webSite.
This is a great way to do E-Commerce SEO. Get your products listed on Amazon but maintain the inventory directly from your own webSite!