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             Christopher B                                                 
             Ferris                                                        
             <chrisfer at us.ibm.                                          To 
             com>                      Mark Nottingham <mnot at mnot.net>,    
             Sent by:                                                   cc 
             openstack-bounces         "openstack at lists.launchpad.net"     
             +zhuadl=cn.ibm.co         <openstack at lists.launchpad.net>     
             m at lists.launchpad                                     Subject 
             .net                      [Openstack] WADL [was: v3 API draft 
                                       (update and questions	to	the  
                                       community)]                         
             2012-06-15 ä¸?å??                                               
             09:57                                                         
                                                                           
                                                                           
                                                                           
                                                                           




+1

Over-reliance on WADL will only make it more challenging to gracefully
evolve the APIs such that implementations can be forwards and/or backwards
compatible, especially when exchanging XML based on an XSD that is not
carefully crafted with proper extensibility points incorporated throughout
the schema design, unless we were to adopt XSD1.1 which has an optional
open content model (but which has not yet seen wide adoption, sadly).

Cheers,

Christopher Ferris
IBM Distinguished Engineer, CTO Industry and Cloud Standards
Member, IBM Academy of Technology
IBM Software Group, Standards Strategy
email: chrisfer at us.ibm.com
Twitter: christo4ferris
phone: +1 508 234 2986


-----openstack-bounces+chrisfer=us.ibm.com at lists.launchpad.net wrote: -----
To: "Nguyen, Liem Manh" <liem_m_nguyen at hp.com>
From: Mark Nottingham
Sent by: openstack-bounces+chrisfer=us.ibm.com at lists.launchpad.net
Date: 06/14/2012 08:34PM
Cc: "openstack at lists.launchpad.net" <openstack at lists.launchpad.net>
Subject: [Openstack] WADL [was: v3 API draft (update and questions to the
community)]

Hi Liem,

I'm one of the folks who helped Marc get WADL off of the ground. At the
time, my use cases were exactly as you describe: documentation (e.g., <
https://github.com/mnot/wadl_stylesheets>) and testing.

Even back then, there was a lot of discussion in the community; e.g., see:
   http://bitworking.org/news/193/Do-we-need-WADL

http://old.nabble.com/Is-it-a-good-idea-to-make-your-WADL-available--tc6087155r1.html


http://www.25hoursaday.com/weblog/CommentView.aspx?guid=f88dc5a6-0aff-44ca-ba42-38c651612092


I think many of the concerns that were expressed then are still valid --
some even within these limited uses. In no particular order:

* People can and will use WADL to represent a "contract" to a service
(really, an IDL), and "bake" client code to a snapshot of it in time. While
it's true that the client and server need to have agreement about what goes
on the wire and what it means, the assumptions around what guarantees WADL
makes are not well-thought-out (in a manner similar to WSDL), making
clients generated from it very tightly bound to the snapshot of the server
they saw at some point in the past. This, in turn, makes evolution /
extension of the API a lot harder than it needs to be.

* WADL's primitives are XML Schema datatypes. This is a horrible match for
dynamic languages like Python.

* WADL itself embodies certain patterns of use that tend to show through if
you design for it; these may or may not be the best patterns for a
particular use case. This is because HTTP and URLs are very flexible
things, and it isn't expressive enough to cover all of that space. As a
result, you can end up with convoluted APIs that are designed to fit WADL,
rather than do the task at hand.

>From what I've seen, many developers in OpenStack are profoundly
uninterested in working with WADL. YMMV, but AFAICT this results in the
WADL being done by other folks, and not matching the reality of the
implementation; not a good situation for anyone.

What we need, I think, is a specification of the API that's precise,
unambiguous, and easy to understand and maintain. I personally don't think
WADL is up to that task (at least as a primary artefact), so (as I
mentioned), I'm going to be proposing another approach.

Cheers,



On 15/06/2012, at 2:08 AM, Nguyen, Liem Manh wrote:

> IMHO, a well-documented WADL + XSD would say a thousand words (maybe
more)...  And can serve as a basis for automated testing as well.  I
understand that the v3 API draft is perhaps not at that stage yet; but,
would like to see a WADL + XSD set as soon as the concepts are solidified.
>
> Liem
>
> -----Original Message-----
> From: openstack-bounces+liem_m_nguyen=hp.com at lists.launchpad.net [
mailto:openstack-bounces+liem_m_nguyen=hp.com at lists.launchpad.net] On
Behalf Of Mark Nottingham
> Sent: Tuesday, June 12, 2012 8:43 PM
> To: Gabriel Hurley
> Cc: openstack at lists.launchpad.net
> Subject: Re: [Openstack] [keystone] v3 API draft (update and questions to
the community)
>
>
> On 13/06/2012, at 1:24 PM, Gabriel Hurley wrote:
>
>> Totally agree with all of Jay's points, and I also couldn't agree more
with Mark on the importance of being crystal clear, and not operating on
just a "common understanding" which is quickly misunderstood or forgotten.
>>
>> Ideally I'd like to see an OpenStack API feature contract of some
sort... essentially a document describing the FULL list of features, how
those parameters are controlled and how they would interact, and what a
project should do if they do not implement an API feature (hopefully only
for technical reasons such as Keystone paging with LDAP or swift with
complex DB-esque operations). This isn't saying we should have a unified
API spec, I'm talking solely about a contract for the features all APIs
should strive to support.
>>
>> This would be a big project, but everyone would then have a common
agreement about what the user experience of interacting with OpenStack
should be. The project APIs as they stand are siloed and stunningly
inconsistent, and I'd love to work toward fixing that.
>
> Absolutely.
>
> One of my other projects is to rewrite the API as a proper specification
(in a style similar to an Internet-Draft, not that we'd necessarily publish
it as one).
>
> I should have something to show soon; if you're interested in helping
out, that'd be great.
>
> Cheers,
>
>
>> My two cents,
>>
>>   - Gabriel
>>
>>> -----Original Message-----
>>> From: openstack-bounces+gabriel.hurley=nebula.com at lists.launchpad.net
>>> [mailto:openstack-
>>> bounces+gabriel.hurley=nebula.com at lists.launchpad.net] On Behalf Of
>>> Mark Nottingham
>>> Sent: Tuesday, June 12, 2012 7:20 PM
>>> To: Jay Pipes
>>> Cc: openstack at lists.launchpad.net
>>> Subject: Re: [Openstack] [keystone] v3 API draft (update and questions
to
>>> the community)
>>>
>>>
>>> On 13/06/2012, at 3:31 AM, Jay Pipes wrote:
>>>
>>>> This isn't necessarily true. Nova's compute layer goes through a
number of
>>> steps to ensure a semi-transactional nature to certain operations like
>>> resizing. Certain times a query needs to indicate that it intends to
make a
>>> reservation of resources (see quota/reservation system now .. this is
the
>>> SELECT FOR UPDATE paradigm) and other times, the query doesn't care
>>> about such things. In the latter case, there aren't expectations that
the list
>>> returned is 100% accurate according to the state of the database at a
>>> particular timestamp of when the transaction occurred. In this case,
filters
>>> and optimistic pagination works perfectly fine, IMHO.
>>>
>>> That might work, but we need to be crystal-clear about the semantics of
>>> what we're giving back; having it understood between OpenStack projects
>>> isn't good enough.
>>>
>>> I.e., we're not building the APIs just for Horizon; they're for lots of
folks, and
>>> subtle semantics -- even when well-documented, much less when they're
>>> not -- are often misunderstood.
>>>
>>> Cheers,
>>>
>>> --
>>> Mark Nottingham   http://www.mnot.net/
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Mailing list: https://launchpad.net/~openstack
>>> Post to     : openstack at lists.launchpad.net
>>> Unsubscribe : https://launchpad.net/~openstack
>>> More help   : https://help.launchpad.net/ListHelp
>>
>>
>>
>> _______________________________________________
>> Mailing list: https://launchpad.net/~openstack
>> Post to     : openstack at lists.launchpad.net
>> Unsubscribe : https://launchpad.net/~openstack
>> More help   : https://help.launchpad.net/ListHelp
>
> --
> Mark Nottingham   http://www.mnot.net/
>
>
>
>
> _______________________________________________
> Mailing list: https://launchpad.net/~openstack
> Post to     : openstack at lists.launchpad.net
> Unsubscribe : https://launchpad.net/~openstack
> More help   : https://help.launchpad.net/ListHelp

--
Mark Nottingham   http://www.mnot.net/




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