[occi-wg] OCCI MC - State Machine Diagram
Roger Menday
roger.menday at uk.fujitsu.com
Thu May 14 07:07:53 CDT 2009
On 14 May 2009, at 12:24, Sam Johnston wrote:
> On Thu, May 14, 2009 at 12:52 PM, Roger Menday <roger.menday at uk.fujitsu.com
> > wrote:
>
> On 14 May 2009, at 10:59, Alexis Richardson wrote:
>
> +1 to Sam's "we may need to revisit this point in the name of interop"
>
> I'm not sure if this is *just* an interop thing ...
>
> I thought my suggestions yesterday on how to transition state, error
> reporting, handling 'processing' states, etc ... were reasonable.
>
> Kind of disappointed this morning that I didn't get some feedback
> from you guys ... :(
>
> Roger, I was working on OCCI until 5am this morning and while this
> is by far the most interesting part of the work it's only half of
> the problem. The other half, adoption/marketing, is boring grunt
> work that keeps us organisers very much on our toes, preventing us
> from being responsive at times.
Hi Sam,
I really wasn't questioning your commitment !
I'm interested in learning/participating/influencing - why I was
hopeful for a reply.
Roger
> In particular the absence of consensus around formats has put me in
> a fairly awkward position for my scheduled talk at Prague on Tuesday
> (which was due yesterday) and is jeopardising previously agreed
> deadlines that I have been advertising heavily in my own name. It
> doesn't help that I don't really share your concerns about states
> being a problem and am confident both that what we have will work
> and that it will invariably be refined in due course.
> Thanks for your understanding - I think you would be surprised to
> see how much behind-the-scenes work goes on in constantly driving
> this kind of initiative forward, which is why one has to be 100%
> committed to, and believe in, the cause.
>
> Sam
>
>
>
> At this stage we are shooting for a draft. The draft will let people
> implement prototypes which will let us debug interop and refine the
> model.
>
>
> On Thu, May 14, 2009 at 10:55 AM, Sam Johnston <samj at samj.net> wrote:
> On Thu, May 14, 2009 at 10:23 AM, Andre Merzky <andre at merzky.net>
> wrote:
>
> Quoting [Sam Johnston] (May 13 2009):
>
> Yes, me, I don't think HATEOAS should be applied in this
> context. But I realise/accept that I maybe the only one
> with that opinion - thats ok. So I'll say it here one last
> time, for the record, and then will shut up: "a static
> simple state model allows for very simple clients.
> Extensions can be defined via substates, or additional
> transitions."
>
> I would counterargue that HATEOAS allows for even simpler clients
> because they don't have to worry about hardwiring even a simple
> state
> model. Using HTTP we can even feed them plain $LANG descriptions of
> what the transitions and targets are - it doesn't get any easier
> than
> that and you don't have to worry about updating clients to implement
> new goodies.
>
> I don't see that. If I want to write a client tool which
> starts a resource, I want to make sure the resource is in
> RUNNING state when the client reports success. But if that
> client (a) has to infer the available states from a
> registry, it cannot posisbly know which state has the
> semantic meaning of RUNNING attached. Further (b), if the
> client only sees those state transitions it is allowed in
> its current state, how does it know what transition path to
> take to reach that target state? Is it (I am making those
> up obviously):
>
> INITIAL -> create() -> CREATED -> elevate() -> ELEVATED () -> run()
> ->
> RUNNING
>
> or
>
> INITIAL -> create() -> CREATED -> init() -> INITIALIZED -> run() ->
> RUNNING
>
> Or should the tool simply fail because it cannot see a run()
> transition in its INITIAL state?
>
> The client must at least know how to create a resource and when it
> has done
> so successfully a "start" actuator will appear, perhaps with a
> target state
> of "running" (TBD). In that case it knows that if it pulls the "start"
> handle eventually the resource should end up "running". Otherwise it
> could
> know (from the registry) that "start" is the right button to push, but
> that's starting to break HATEOAS principles. We have options - it's
> just a
> matter of finding the right one.
>
>
> I think HATEOAS works pretty well if a human is in the loop
> who can parse the available transition description, and
> deduce a semantic meaning. I don't think it makes for
> simple tooling, really.
>
> I agree that humans are better at this stuff than computers but I'm
> unconvinced this translates to complex tooling.
>
>
> Then again, I may misunderstand the proposed usage of
> HATEOAS in OCCI. So, can you help me out: what mechanism
> will avoid the confusion from the example above, if a vendor
> can provide init() and elevate() transitions on the fly,
> with no predefined semantics attached? How would my tool
> deduce the transition path it needs to enact?
>
> The semantics for common functions will be in the registry. It's
> ones that
> are uncommon and impossible to predict like "translate" and
> "migrate" that
> we're catering for here, and generally there will need to be some
> kind of
> client side support for these.
>
> As I said below, "we may need to revisit this point in the name of
> interop",
> and I suggested categories as one possible solution (e.g. a
> "starting" vs a
> "stopping" transition)... parametrised transition calls are
> another... for
> example, how do I tell something to start *without* saved state if
> saved
> state is present (ala cold start vs resume)?
>
> Sam
>
>
> I don't think anyone knows every possible thing that users are going
> to
> want to do with the API (I certainly don't have the confidence to
> say
> I
> do anyway) but we may need to revisit this point in the name of
> interop... Atom categories would be one way to achieve this (e.g.
> "Cold
> Reboot" and "Warm Reboot" might go in the "restart" category).
> Sam
>
> References
>
> 1. mailto:andre at merzky.net
>
>
>
> --
> Nothing is ever easy.
>
>
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>
> Roger Menday (PhD)
>
> <roger.menday at uk.fujitsu.com>
>
> Senior Researcher, Fujitsu Laboratories of Europe Limited
> Hayes Park Central, Hayes End Road, Hayes, Middlesex, UB4 8FE, U.K.
> Tel: +44 (0) 208 606 4534
>
>
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Roger Menday (PhD)
<roger.menday at uk.fujitsu.com>
Senior Researcher, Fujitsu Laboratories of Europe Limited
Hayes Park Central, Hayes End Road, Hayes, Middlesex, UB4 8FE, U.K.
Tel: +44 (0) 208 606 4534
______________________________________________________________________
Fujitsu Laboratories of Europe Limited
Hayes Park Central, Hayes End Road, Hayes, Middlesex, UB4 8FE
Registered No. 4153469
This e-mail and any attachments are for the sole use of addressee(s) and
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use or copying for disclosure is strictly prohibited. The fact that this
e-mail has been scanned by Trendmicro Interscan and McAfee Groupshield does
not guarantee that it has not been intercepted or amended nor that it is
virus-free.
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