Doug,
On Thu, 12 Apr 2007, Doug Tody wrote:
>>> What is important is to get the underlying messaging model right.
>>
>> I'm not trying to be funny, but: why? Leaving aside any difficulties
>> about coming to agreement on the details of such a model, can you
>> explain what you see as the practical advantages of having a "right"
>> messaging model ...
>
> This is extremely important, as it will be the basis for all
> the message-related protocols which are layered on top of it,
> and the basis for all messaging-related software implementations.
> A model like this tends to get built into all software which uses it.
> It defines the basic semantics of how you do messaging.
The benefits that you list sound to me more ideological than practical. As you can probably tell, I am somewhat (though not totally) sceptical that designing a multi-layered model-based abstract generalised messaging architecture followed by separately designing multiple alternative prescriptive specifications of how to implement this, as opposed to starting with the specifications of what applications need to do in order to talk to each other, is the best way to go about things. Such additional layers of abstract design *may* pay dividends, but only if it turns out that new messaging situations arise which both are difficult/impossible in the basic profile and must/should share part of their specification with it, and it's not clear to me that that will be the case. Such multi-layered approaches also face dangers not presented by one-size-fits-all designs, such as the possibility of partial implementations and of "compliant" implementations or messages which are mutually incompatible. Whether I am being admirably pragmatic or woefully short-sighted here will only be answered by future developments.
However, we're probably not going to progress further on this by continuing to argue about it. Some people in the debate are more concerned with how the data model underlying messaging is formulated (with a view to permitting various different implementation profiles as needs arise in the future), and others are more focussed on sorting out the nuts and bolts of what an application has to do in order to participate in a messaging or data-sharing conversation, in particular on issues like bootstrapping a connection with the hub and selection of a wire protocol. To some extent these concerns are orthogonal (though of course the former will influence the latter), so I think we should be able to come up with something satisfactory to both sets of interests without too much disagreement.
*If* we go down the route of revolution (scrapping PLASTIC as it stands and replacing it with something which can do similar things but which may have advantages such as more flexibility and securer theoretical underpinnings) rather than evolution (incremental modifications of the existing PLASTIC standard to allow it to do new things where new capabilities are required), then I am happy that this is done along lines similar to those that Mike and Doug are advocating, although there are still matters of detail to address. I agree with the comment:
> Also: this does not have to be all that hard. I don't think we are
> far from having such a basic messaging model. What Mike outlined
> earlier, with some more work along the lines of these discussions,
> would probably work for our applications (not just for high level
> inter-tool messaging).
as far as it applies to the task of specifying a standard from scratch: what will require some effort however is reworking existing code in PLASTICised applications (and, less importantly, in hub implementations), and organising things such that the changeover between the existing and future messaging systems does not leave users with tools on the desktop unable to to communicate because they speak different messaging protocols.
The opinions in this message are basically my personal ones; I've got some idea, but I'm not sure, how far they are shared by other active and passive participants in the debate, and I don't wish to push them if they are not widely shared. It might be a good point for such participants who have an interest or opinion (particularly those who hope in the short or long term to adopt whatever it is we end up agreeing on) to provide input about where they stand on these issues.
Mark
P.S. I should mention that I will be away all next week; I understand
that John Taylor and Alasdair Allan will also be busy.
-- Mark Taylor Astronomical Programmer Physics, Bristol University, UK m.b.taylor@bris.ac.uk +44-117-928-8776 http://www.star.bris.ac.uk/~mbt/Received on 2007-04-13Z16:35:53