[ogsa-rss-wg] Candidate Ordering Language

[Donal K. Fellows]

Ramin Yahyapour wrote:
> I assume Donal just want to be able to calculate with time
> as well as with other scalar values in this ordering language.
> That means, you might want to write
> "order by (x*starttime + y*CPU#)"
> In that case it is essential how starttime is mapped to a scalar
> value.

Exactly. The only other way is to assume some standard "time zero" but
that's even less pleasant in practice. Base times are just easier to
work with.

> I assume Donal is trying to model an individual objective function
> for a candidate request. In this request someone may specify some
> complex function which can be evaluated to get a scalar value for
> each candidate. This value can be used for ordering.

Yes.

> Otherwise, the language is fine for me.
> At our site we did a similar approach in the past. However, we built a richer
> language in which we allowed conditional statements (if/then).
> Assuming that part of your ordering formulation might depend on the
> availability of certain resource features you might shift your weights
> and the complete function. Let's say, if memory is below 4GB you would
> put more weight on this feature, if it is above, you might focus on other
> values like price or responsetime.

Actually, you can effectively do this using the result of the <exists>
term (a zero-or-one value):

  <sum>
    <product>
      <exists> //Memory[. < 4000000000] </exists>
      ...
    </product>
    <product>
      <exists> //Memory[. >= 4000000000] </exists>
      ...
    </product>
  </sum>

Or something like that.

> But anyway, we should not make this language too complicated at this point.
> Thus I would suggest to restrict on basic features. Adding more complexity
> later should not be a problem here.

Agreed.

Donal.