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19248Re: [rest-discuss] API versioning

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  • Keith Hassen
    Jan 8, 2013
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      First of all, thanks for the replies and perspective on REST.

      Backing up to the original question it seems like your particular take on it is that there's no need to version URIs or the resource representations provided that a cautious approach is taken to resource evolution.

      To be honest I'm still not sure how this would be handled if two clients diverge in their understanding of the same resource.  Perhaps that divergence leads us to different concepts and thus different resources and I've just been thinking about the problem incorrectly. :)

      Back to your most recent response...

      This seems to be a recommended practice that I've encountered in
      reading about RESTful implementations.


      Perfectly good HTTP API practice; REST, not so much.  The point of
      media types is to provide loose coupling based on shared understanding
      of how the representation is to be decoded.  

      I think I'm actually talking about loose coupling, but this area seems a little fuzzy.  Comprehensive coverage of media type seems to be missing from Fielding's dissertation.  The media type I specified was definitely too specific (vnd.example.com might be a better choice rather than vnd.example.com.order, the latter effectively binding the media type to the representation and starts smelling like RPC modelling rather than the loose coupling promoted by the RESTful style).

      So how tight should this coupling be?  And what about versioning?  I'm tempted to say that if versioning is required, do so in the URi rather than the media type.  The media type seems to be more of an assertion/expectation regarding application context rather than a specification of the resource.

      It's amazing (or maybe not at all amazing) how divided this subject appears to be on the web.  This: http://www.informit.com/articles/article.aspx?p=1566460 is a pretty typical example.

      Thanks again for the feedback.

      K


      On 2013-01-08, at 12:57 AM, Eric J. Bowman wrote:

      Keith Hassen wrote:

      This seems to be a recommended practice that I've encountered in
      reading about RESTful implementations.


      Perfectly good HTTP API practice; REST, not so much.  The point of
      media types is to provide loose coupling based on shared understanding
      of how the representation is to be decoded.  Not tight coupling based
      on interpreting the content of the representation.  I've never seen an
      order API that couldn't be represented as HTML; despite any number of
      variations on this theme (or versions within), the media type doesn't
      vary between more order APIs on the Web than I can count.

      REST has no notion of resource "type" let alone of exposing same on the
      wire, so I've never understood why this solution is so prevalent in REST
      discussions.  Just media types, which are agnostic as to what "type" of
      resource is being represented (with rare exceptions as parameters).


      Anything else is up to the user-agent to work out.  This is actually
      easier for m2m than h2m; a v1 m2m client should already ignore any
      hypertext it doesn't understand, rolling out v2 can then re-use any
      non-deprecated bits of the API already present plus the new stuff,
      and ignore the deprecated stuff.  Can't it?

      Not always, at least not in my experience. :)  I have found that
      while breaking changes don't happen often, they *do* happen.  Add to
      this the possibility of different types of API consumers that start
      off implementing your APIs the same way, but slowly (or rapidly!)
      diverge over time.  In some cases new resources (and thus new URIs)
      will suffice, but in other cases what we are doing is very
      specifically *evolving* the resource representation to accommodate
      new requirements.


      Then design for graceful degradation (or progressive enhancement) using
      client-side feature detection.  Just saying there's no need to swing
      the conneg hammer to turn this particular screw.

      -Eric

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