9. REST Design Guidelines

Some soft guidelines for designing a REST architecture:

1. Do not use "physical" URLs. A physical URL points at something physical -- e.g., an XML file: "http://www.acme.com/inventory/product003.xml". A logical URL does not imply a physical file: "http://www.acme.com/inventory/product/003".
   • Sure, even with the .xml extension, the content could be dynamically generated. But it should be "humanly visible" that the URL is logical and not physical.
2. Queries should not return an overload of data. If needed, provide a paging mechanism. For example, a "product list" GET request should return the first n products (e.g., the first 10), with next/prev links.
3. Even though the REST response can be anything, make sure it's well documented, and do not change the output format lightly (since it will break existing clients).
   • Remember, even if the output is human-readable, your clients aren't human users.
   • If the output is in XML, make sure you document it with a schema or a DTD.
4. Rather than letting clients construct URLs for additional actions, include the actual URLs with REST responses. For example, a "product list" request could return an ID per product, and the specification says that you should use http://www.acme.com/product/PRODUCT_ID to get additional details. That's bad design. Rather, the response should include the actual URL with each item: http://www.acme.com/product/001263, etc.
   • Yes, this means that the output is larger. But it also means that you can easily direct clients to new URLs as needed, without requiring a change in client code.
5. GET access requests should never cause a state change. Anything that changes the server state should be a POST request (or other HTTP verbs, such as DELETE).