Re: SMI clarification

[ANDREASSON <[e-mail]>]

This topic reminds me of the riddles column in some magazines -
I am writing this on the beach ;-)


Olivier Miakinen wrote:
>
> I'm interested in having the answer to your question, and I think
> that people who responded didn't see THE point. Then I cut extra-stuff,
> in order for the `INDEX { t1AltIndex, t1AltIndex }' to appear alone.
>

I think we got 'THE point' - if there was just one variable in the
INDEX clause, there wouldn't be any 'point'.

...

Olivier Miakinen wrote later:
>I suppose that both values are different, because it wouldn't be
>necessary to specify the attribute twice if it was always the same value.
>I mean, you can have an instance of t2Sum that is: t2Sum.7.15, where
>7 is one t1AltIndex value, and 15 is another t1AltIndex value.
>

Yes. Another way to look at the problem is to consider it as a special
case of having one table row be a function of several rows in other
table(s). In the generic case, for example t2Sum.7.15 might be
a different or the same instance as t2Sum.15.7 - (this is implementation
dependent, of course).


>As an other example, if the INDEX clause was:
>   INDEX { t2Sum, t2Sum }
>then I would say this would be impossible, for the following reason:
>If you get t2RowStatus.7.15, you can't know if corresponding t2Sum
>is 7 or 15.

Not really, I would say also the "INDEX { t2Sum, t2Sum }" is both
syntactically and semantically correct. It just implies that the agent
would treat requests for t2RowStatus.x.x as valid, whereas
t2RowStatus.x.y (x!=y) would generate an error. (However, I can hardly
think of a situation where this construction may be of any use...)

Semantically, it's just required of the INDEX clause to provide for a
way to unambiguously identify a row:

(From RFC 1902:)
"
   The instance identification information in an INDEX clause must
   specify object(s) such that value(s) of those object(s) will
   unambiguously distinguish a conceptual row.
   ...
"

...I'll move on to the chess problems column :-)


Sigge Andreasson