5. REST Server Responses

A server response in REST is often an XML file; for exmaple,

<parts-list>
 <part id="3322">
  <name>ACME Boomerang</name>
  <desc>
   Used by Coyote in <i>Zoom at the Top</i>, 1962
  </desc>
  <price currency="usd" quantity="1">17.32</price>
  <uri>http://www.acme.com/parts/3322</uri>
 </part>
 <part id="783">
  <name>ACME Dehydrated Boulders</name>
  <desc>
   Used by Coyote in <i>Scrambled Aches</i>, 1957
  </desc>
  <price currency="usd" quantity="pack">19.95</price>
  <uri>http://www.acme.com/parts/783</uri>
 </part>
</parts-list>

However, other formats can also be used; unlike SOAP services, REST is not bound to XML in any way. Possible formats include CSV (comma-separated values) and JSON (JavaScript Object Notation).

Each format has its own advantages and disadvantages. XML is easy to expand (clients should ignore unfamiliar fields) and is type-safe; CSV is more compact; and JSON is trivial to parse in JavaScript clients (and easy to parse in other languages, too).

One option is not acceptable as a REST response format, except in very specific cases: HTML, or any other format which is meant for human consumption and is not easily processed by clients. The specific exception is, of course, when the REST service is documented to return a human-readable document; and when viewing the entire WWW as a RESTful application, we find that HTML is in fact the most common REST response format...