Information Technology Reference
In-Depth Information
The definition of the runtime requirements adaptation problem reflects the intuition that
by changing the context, the requirements problem may change - as requirements can
change - and from there, a new solution needs to be found to the requirements problem
in the new context.
We now reformulate the requirements problem so as to highlight the role of context
in it, as well as of the resources.
Definition 11.
Requirements problem RP
in context
C
:Given
the elicited or oth-
erwise acquired: domain assumptions in the set
K
,tasksin
T
, goals in
G
, quality con-
straints in
Q
, softgoals in
S
, preference, is-mandatory and is-optional relations in
A
,a
context
C
on which
K
(
C
)
∪
T
∪
G
∪
Q
∪
S
and
A
depend on,
find
all
candidate solutions in
and compare them using preference and is-optional relations from
A
to identify the most desirable candidate solution.
context
C
to RP
(
C
)
Definition 12.
Candidate solution
CS
in the context
C
:
Asetoftasks
T
∗
and a set of
domain assumptions
K
∗
are a
candidate solution in the context
C
to the requirements
problem RP
(
C
)
in context
C
if and only if:
1.
K
∗
and
T
∗
are not inconsistent,
2.
C,
K
∗
,
T
∗
|
cτ
G
∗
,
Q
∗
,where
G
∗
⊆
G
and
Q
∗
⊆
Q
,
3.
G
∗
and
Q
∗
include, respectively, all mandatory goals and quality constraints,
4. all mandatory softgoals are approximated by the consequences of
C,
K
∗
∪
T
∗
,so
that
K
∗
,
T
∗
|
cτ
S
M
,where
S
M
is the set of mandatory softgoals, and
R
(
C
∪
K
∗
∪
T
∗
)
5. resources
needed to realize this candidate solution are available.
As discussed earlier, we view runtime requirements adaptation problem as a dynamic
RE problem. To support the analysis, we add two relations in the CORE ontology. We
now define the
relegation relation
via the inference and preference relations in Techne.
Definition 13.
Relegation relation:
A relegation relation is an (
n
+1
)-ary relation that
stands between a requirement
φ
∈
Δ
and
n
other sets of requirements
Π
1
,Π
2
,...,Π
n
⊆
Δ
if and only if there is an inference relation from every
Π
i
to
φ
and there is a binary
relation:
whereby
Π
i
φ
Π
j
if it is strictly
more desirable to satisfy
φ
by ensuring that
Π
i
holds, than to satisfy
φ
by ensuring that
Π
j
φ
⊆{
Π
i
|
1
≤
i
≤
n
}×{
Π
i
|
1
≤
i
≤
n
}
holds.
The inference relations required by a relegation relations indicate that a relegation rela-
tion can only be defined for requirements that we know how to satisfy in different ways.
For example, if we have a goal
g
(
p
)
, and we have two ways to satisfy that goal, e.g.:
Π
1
=
{
(
q
1
)
,
b
(
(
q
1
)
→
(
p
))
}
(4.9)
t
t
g
Π
2
=
{
(
q
2
)
,
b
(
(
q
2
)
→
(
p
))
}
(4.10)
t
t
g
then we have satisfied the first condition from the definition of the relegation relation,
since
Π
1
|
cτ
.
The second condition in the definition of the relegation relation says that we need to
define a preference relation
(
p
)
and
Π
2
|
cτ
(
p
)
g
g
g
(
p
)
between different ways of satisfying
g
(
p
)
.Observe
that we define
g
(
p
)
between
sets
of information, not pieces of information. The Techne
