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the algorithm, we may obtain several solutions to a specific WSC
problem. For each feasible one, according to the QoS parameters of
each component service, we can compute the value of QoS parameters
of the whole composite service as shown in Chapter 5. Then we can
select the best solution that can satisfy user requirements for QoS
parameters and have the optimal performance.
For a Type I user preference, that is,
conditions
?WS
1
:WS
2
, we use
the PPCE algorithm as follows.
Algorithm PPCE. Processing Preference with Conditional
Expression
1.
w
0
;
w
00
g
V
ð
S
0
Þ then
if
A
¼f
Suppose that
n
0
A
;
n
0
A
2
2.
NS
temp
representing the action nodes
corresponding to services
w
0
and
w
00
respectively;
3.
;
4. According to state
S
0
, examine whether the truth value of
Cond
in user preference can be found;
flag
¼ false
5.
if
found to be true
then
6.
Introduce a decision node into the diagram, and draw a connector
from
n
0
to it;
7.
flag
¼ true
;
n
0
A
;
n
0
A
g
8.
else if
, such that the
truth value of
Cond
can be found to be true under its corre-
sponding state
S
k
there is some node
n
k
2
NS
temp
f
then
9.
Introduce a decision node into the diagram, and draw a connector
from
n
k
to it;
flag
¼ true
10.
;
else
11.
Suppose
NS
0
¼
n
0
A
;
n
0
A
g
;
12.
NS
temp
f
NS
0
13.
while
6¼
f
do
NS
0
with state
S
t
;
14.
8
n
t
2
15.
if
S
t
O
E
then
;
NS
0
¼
NS
0
f
16.
RS
¼
RS
[f
n
t
g
n
t
g
;
NS
¼
NS
f
n
t
g
;
17.
else
18.
According to
S
t
, do one step reasoning to obtain all the
executable services, denoted
V
(
S
t
);
NS
t
¼
f
;
19.
20.
for
each service
w
2
V
ð
S
t
Þ do
