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if the system asks the user a question of the form: Your flight is delayed by 5 hours or
more. Do you wish to rebook a flight for the next day? This question can be reformulated
as a question on which of these two formulas to add to the current context of the user
(i.e. the context in which we asked the user that question):
c
(
c
(
p
)
g
(
q 1 ) →⊥ )
(4.6)
c
(
c
(
p
)
g
(
q 2 ) →⊥ )
(4.7)
where c
(
p
)
is for “flight delayed by more than 5 hours”, g
(
q 1 )
is for the goal “keep the
booked flight”, and g
is for the goal “rebook the same flight for the next day”. If the
user answers “yes”, then add formula c
(
q 2 )
(
(
p
)
(
q 1 )) →⊥
to the context in which we
asked the user that question; if the user answers “no”, then we add c
c
g
(
(
p
)
(
q 2 )) →⊥
c
g
to the current context.
We now add the Resource concept. Since the formal language that we use in this
paper is propositional, we will keep the resource concept out of it.
Definition 8. Resource: An instance R of the Resource concept is an entity referred to
by one or more instances of Communicatedinformation .
In order to introduce resources in the definition of the runtime requirements adaptation
problem, we need a function that tells us which resources are referred to by a task,
domain assumption, or a context proposition, as these resources will need to be available
and used in some way in order to ensure that the relevant domain assumptions and
context propositions hold, and that the tasks can be executed.
Definition 9. Resource selector function: Let C be the set of all contexts. Given a set of
tasks, domain assumptions, and/or context propositions, the resource selector function
returns the identifiers of resources necessary for the domain assumptions and/or context
propositions to hold, and/or tasks to be executed:
C
R :
(
T
K
) −→
(
R
)
(4.8)
The domain of
are domain assumptions, context propositions, and tasks. The reason
that goals, softgoals, and quality constraints are absent is that the resources will be
mobilized to realize a candidate solution to the requirements problem, and the candidate
solution includes only domain assumptions and tasks. Since these domain assumptions
and tasks are contextualized, we need to ensure the availability of resources that are
needed in the context on which these domain assumptions and tasks depend on. Note
also that we have C because C is a set of sets, so that we need to get the union of all
of the sets in C .
We can now formulate the runtime requirements adaptation problem for SAS .
R
Definition 10. Runtime requirements adaptation problem: Given a candidate solu-
tion CS
(
C 1 )
in the context C 1
C to the requirements problem RP
(
C 1 )
in context
C 1
C , and a change from context C 1
to C 2 =
C 1 , find the requirements problem
RP
(
C 2 )
in context C 2
C and choose among candidate solutions to RP
(
C 2 )
a solution
CS
(
C 2 )
in the context C 2 to the requirements problem RP
(
C 2 )
in the context C 2
C .
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