openstack team mailing list archive

[Doug Davis <dug@xxxxxxxxxx>]

I don't see this as an either-or type of thing. 

Totally agree with Mark that the APIs need to be more clearly documented 
and that should be independent of any kind of IDL (ala WADL) artifact.  I 
say this mainly because I think we always need to have something that's 
human readable and not machine readable.  There will always be semantics 
that can not be expressed via the machine readable artifacts. Having said 
that, there are people that like to have IDL-like artifacts for some kind 
of tooling.  So, along with the well-documented APIs should be whatever 
artifacts that can makes people's lives easier.  This means XSD, WASL, 
WSDL, etc... whatever - pick your favorite. 

No matter what artifact you choose to use to guide your coding (even if 
its just the "well documented human readable API doc"), you're still bound 
to that particular version of the APIs.  Which means a change in the 
APIs/server-code might break your client.  In this respect I don't think 
WADL or docs are more or less brittle than the other.  To me the key 
aspects are the extensibility points.  Once the APIs are deemed 'stable', 
we just need to make sure that new stuff is backwards compatible which 
usually means defining and leveraging well placed extensibility points. 

thanks
-Doug
______________________________________________________
STSM |  Standards Architect  |  IBM Software Group
(919) 254-6905  |  IBM 444-6905  |  dug@xxxxxxxxxx
The more I'm around some people, the more I like my dog.



Mark Nottingham <mnot@xxxxxxxx> 
Sent by: openstack-bounces+dug=us.ibm.com@xxxxxxxxxxxxxxxxxxx
06/14/2012 08:20 PM

To
"Nguyen, Liem Manh" <liem_m_nguyen@xxxxxx>
cc
"openstack@xxxxxxxxxxxxxxxxxxx" <openstack@xxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxx 
[mailto:openstack-bounces+liem_m_nguyen=hp.com@xxxxxxxxxxxxxxxxxxx] On 
Behalf Of Mark Nottingham
> Sent: Tuesday, June 12, 2012 8:43 PM
> To: Gabriel Hurley
> Cc: openstack@xxxxxxxxxxxxxxxxxxx
> 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@xxxxxxxxxxxxxxxxxxx
>>> [mailto:openstack-
>>> bounces+gabriel.hurley=nebula.com@xxxxxxxxxxxxxxxxxxx] On Behalf Of
>>> Mark Nottingham
>>> Sent: Tuesday, June 12, 2012 7:20 PM
>>> To: Jay Pipes
>>> Cc: openstack@xxxxxxxxxxxxxxxxxxx
>>> 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
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>> 
>> 
>> 
>> _______________________________________________
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> 
> --
> Mark Nottingham   http://www.mnot.net/
> 
> 
> 
> 
> _______________________________________________
> Mailing list: https://launchpad.net/~openstack
> Post to     : openstack@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~openstack
> More help   : https://help.launchpad.net/ListHelp

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




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