[ogsa-wg] Thoughts on extensions mechanisms for the HPC profile work

[Donal K. Fellows]

Marvin Theimer wrote:
> Regarding your suggestion for having a runtime meta-language for marking 
> content as "ok to ignore" or must be understood", I have several 
> questions/requests:
> 
>     * When you say "meta-language" are you implying something richer
>       than these two choices?  I can imagine at least two answers to
>       this question:
>           o "Simple" (and hence also efficient) resource matchmaking
>             typically involves (mostly) exact matches.  Adding a simple
>             binary notion of an optional resource requirement adds a
>             powerful descriptive capability without substantially
>             complicating the matchmaking system.

It would be so nice if that was true. Simple matchmaking comes in two
varieties according to the basic type of the resource being matched.
Capabilities (like the ability to run a particular application) are
straight matched as described, but capacities are typically matched
according to the scheme where a user wants "at least this much" and the
provider has "at most that much" so it's really testing for inequality
satisfiability or set overlap.

What's more, alternatives are another one of these things that seems to
be distinctly confusing, especially as it turns out to be very difficult
for users to really understand the space of potential alternatives open
to them. A better approach seems to be for users to specify their *real*
requirements, and for some kind of intermediate agent to translate from
those into terms understood by the resource providers.

>           o You want a much more expressive resource
>             description/matchmaking language that lets you specify all
>             kinds of complicated concepts, such as prioritization of
>             optional alternatives.

Personally, I think that prioritization sucks. Scoring (which is sort-of
but not quite the same thing) works better as it is far more flexible.
It's also easier to apply to things other than the initial job request;
far better to say "I prefer cheapest/quickest" after getting the tenders
than to try to figure out what the space of tenders is going to look
like before soliciting for them.

Donal (I suspect I'm not being clear enough...)