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Re: Homework Question
At 09:04 PM 2/17/2003 -0700, you wrote:
Hi --
I have a clarification question on homework problem III.
The diagram suggests that a partial ordering has already been determined
in the sense that A1 < A2 and B1 < B2. If A2--Q-->G, then is A1
considered a threat to that causal link?
A threat is an action that can "possibly come between the source and the
destination steps and delete the condition". If A1 is necessarily before A2
then it cannot possible come between A2 and G.
Or can it be disregarded as a threat because the ordering A1 < A2 has
already been determined? A similar question may be asked of B2--P-->G and B1.
I suspect that the point of III.b is that is that it is not possible to
give causal links for the plan such that all causal links are
threat-free. But if the previously mentioned situations are not
considered threats, and if we are assume that the partial ordering has
already been determined, then it seems possible that there is a set of
threat-free causal links for the plan. With A2--Q-->G, A1--R-->A2,
B2--P-->G, and B1--S-->B2.
The point of the question is to make you realize that causal links are
sufficient but not necessary for ensuring that the plan is correct (a
partial order plan is correct if every one of its topological sorts will
necessarily achieve all the goals on execution).
Rao
Or perhaps I am misunderstanding what the question is asking.
Another interpretation of the question which was suggested to me was based
on the fact that the question statement says "such that ALL causal links
are threat-free." Therefore, given that A2--P-->G is not threat-free,
even if it is possible to construct a plan without establishing A2--P-->G
as a causal link, it is not true that "ALL causal links are threat-free."
Because the list of ALL POSSIBLE causal links that could be established
for the plan would include at least one causal link with a threat. But I
don't believe that this is what you are asking.
Can you help clarify this, please?
-- Andrew Davis
drewdavis00@hotmail.com
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