While the W3C's Technical Architecture Group (TAG) argues about the safety of various flavors of HTTP programming, two icons of the Web have gone different directions: Google toward SOAP, and Amazon (whether they know it or not) toward REST.

The Google SOAP API has been fairly widely reported and is built on SOAP and WSDL.

The Amazon approach (Associates account required) is very different, relying only on a simple XML vocabulary and queries built on HTTP GET. While intended only for Amazon Associates to build more sophisticated catalogs, it offers a similar level of information to Google's offering.

The DTD for the vocabulary is very simple XML: just elements, no attributes or namespaces. No SOAP wrapper is used. A GET-based query contains the information associates are requesting, along with their ID:

http://rcm.amazon.com/e/cm?t=[Associates ID goes here]
&l=st1&search=[subject keyword goes here]
&mode=[product line goes here]
&p=102&o=1&f=xml

The combination of a GET request and XML response should be enough to take care of requests from Associates, as Associates are accessing information, not changing information.

Amazon requests that developers only use the information for Associates-site development, and that they restrain queries to once per day per query.