Information Technology Reference
In-Depth Information
Change to
context
C
1
Change to
context
C
2
Current
context:
Current
context:
C
1
C
2
Time
System still works according to
solution:
System works according to solution:
System works according to solution:
CS(C
1
)=(K
C
1
;T
C
1
)
CS(C
1
)=(K
C
1
;T
C
1
)
CS
(C
2
)=(K
C
2
;T
C
2
)
That solution
solves:
RP(C
1
)
But that solution is inadequate,
because problem is now:
RP(C
2
)
That solution
solves:
RP(C
2
)
Time after Adaptation to satisfy
context
C
2
Time before Adaptation in
Context
C
1
Time during Adaptation as per change
in context from
C
1
C
2
to
Fig. 2.
System Adaptation Sequence in Time
candidate solution
CS
. At this SAS may perform at sub-optimal level and can exploit
automated reasoning techniques such as planning or decision making techniques such
as analytic hierarchy process (AHP)
3
.
Before Adaptation:
Assume that at time
t
1
, the user's goals
G
∗
are
to connect to the
Internet for checking details of itinerary
and
inform about the flight delays
with the
quality constraint
Q
to have the Internet connectivity not less than 256Kbps
. To satisfy
these requirements, SAS is running according to its candidate solution
CS
i.e., using
the set of tasks
T
∗
,e.g.
search for available connection
,
enable Wi-Fi
,
get itinerary
details
and
show flight itinerary
, in the current context i.e.
C
1
is
at the airport
,andthe
domain assumption
K
t
1
Internet must be available at the airport
, is not violated. This
implies that,
CS
K
C
1
,T
C
1
)
(
C
1
)
=
(
and
CS
(
C
1
)
satisfies the runtime requirements
adaptation problem i.e.
RP
(
C
1
)
. We can rewrite this as:
G
C
1
,
Q
C
1
C
1
,
K
C
1
,
T
C
1
|
cτ
R
(
C
1
∪
K
C
1
∪
T
C
1
)
where
identifies the set of resources
R
available, e.g. (Airport Wi-Fi
hotspot, Mobile Phone of the user) to perform
T
C
1
.
During Adaptation:
SAS while executing
CS
, observes a change in context i.e.
the airport Wi-Fi connection becomes unavailable
at time
t
2
. Due to this change in
context from
C
1
to
C
2
, the existing candidate solution
CS
(
C
1
)
might be valid but is
not adequate to satisfy the current context
C
2
. As a consequence, the SAS needs to re-
evaluate its candidate solutions
CS
by searching in its solution base i.e.
Δ
or looking
for solutions that can be realized through available services. For instance, a new candi-
date solution
CS
(
C
1
)
could be, e.g.
connect to the Internet using data services either
3G or Edge on mobile phone
R
;or
recommending user to move to the area where the
signal strength is stronger
;or
avail the Internet on the free booths
. At this stage, SAS
(
C
2
)
3
Discussing such techniques are out the scope of this paper. We present three scenarios to
illustrate how the SAS can adapt at runtime by resolving the runtime requirements adaptation
problem.
