[ogsa-rss-wg] Candidate Ordering Language

[Donal K. Fellows]

Sorry for not getting back to you earlier, but I was on vacation.

Arvid Norberg wrote:
> The documents those XPath queries are looking in wasn't really
> discussed. I presume that document is supposed to describe the
> properties of a particular resource (which is to be ranked).

A Candidate Execution Plan is a document containing a reference to a BES
container, a JSDL document to submit to that container, and a QoS
estimate (a place to describe things like the likely cost, delay between
submit and start, etc.) It might contain other things too (such as a
suggested CDDLM deployment descriptor or a proposed WS-Agreement
template) but they're optional (and out of scope too).

> The example suggests having a whole jsdl document, which I'm not
> sure makes alot of sense. There's no Application, file staging
> or project involved.

In general, the JSDL document might be rewritten as part of the
candidate generation process. This would allow the original JSDL to
contain (for example) application-specific extension terms that are
mapped by the EPS to standard terms understood by the BES container.
This is an approach I've used with good success in several projects, and
it's one of the best ways I've seen of coupling the basic service grid
with higher level application grids.

> The Resources element (from the jsdl spec) on the other hand is
> (probably) capable of describing all important properties of a
> resource. It could even contain the name/URL of the BES in
> Resources/CandidateHosts/HostName.

It can't describe the executable path (which is not equal to the
application name and version!) arguments, environment variables or
system limits, all of which are needed for some apps on some platforms.
Of course, users could figure all that out for themselves, but that's
just plain stupid as it is forcing them to know about installation-
specific details even though there is a mechanical selection step in the
overall process.

Full JSDL documents come back in the Candidate for good reason. It's not
by whim or wilful misdesign (it would have been nice if it was possible
to leave it out as that would make the EPS implementations have a much
higher limit efficiency) but rather a key aspect that has to be there
for the overall vision to work at all.

Donal.