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33.
for each action node n j 2
RS
do
34.
Draw a connector from n j to n f ;
35.
end for
36.
end if
37. Remove all the action nodes that cannot be connected to the finial
node n f from the diagram, and also their associated connectors;
38. Since each path from the initial node to final node in the generated
diagram is a feasible solution to the service composition problem,
partition the diagram into several activity diagrams while keeping
each conditional branch structure in every composite service since
a branch structure cannot be divided.
In the algorithm, each action node n j in the generated activity
diagram represents an available service from community
. Moreover,
an information state S j is associated with n j to denote the current status
after executing the service that the node represents. It contains the
currently available input and output parameters, as well as information
indicating the conditions that are presently true. These paramaters are
used in the next step reasoning. In service composition based on input
and output parameters only, state S j can be just a collection of
parameters obtained by executing a sequence of services—starting
from the initial node, and ending at the current node along a path of
the diagram. The associated state of the initial node n 0 is S 0 ¼
C
I A , which
is the set of available inputs that the service requester provides. At S j ,we
have a set of services V ð
, each of which can be invoked.
After every step of reasoning, we check the set of newly obtained
executable services to see whether any concerned service mentioned in
Pref appears or not. If yes, we have to introduce a branch structure into
the activity diagram under certain conditions as given in Pref .
At the end of the algorithm, the set RS records all the action nodes
whose corresponding states can satisfy the user requirement. According
to these nodes, we can find all the feasible solutions from the con-
structed diagram. RS
S j Þ
¼ 1 indicates that there are no solutions to this
WSC problem.
It is worth noting that we can use any existing reasoning method to
compute state S j and the set of invocable services V ð
under S j in
the algorithm. Many such methods can do this job. Some simple ones
are based only on inputs and outputs of services [153], while others are
based on inputs, outputs, preconditions, and effects [154]. At the end of
S j
Þ
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