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Through this example, we can see that data-driven approach is well
suited for service composition provided that the business/service data
and their relations are available.
3.6 DISCUSSION
In the proposed data-driven approach, we use a subnet decomposition
technique to generate all conflict-free solutions. Note that our definition
of conflict-freeness (Definition 3.4) allows choices over mediation
transitions such that a generic data type can be classified into its child
types. We believe that the decomposition-based approach is an efficient
way to find some feasible solutions. If a desired solution is required to
have conflicts, users can easily change the definition of selection tuple
(Definition 3.8) from one to multiple branches for each conflict place.
By this means, more subnets are obtained and can contain cyclic nets if
choices are allowed.
Although our algorithm can be easily adapted to this scenario that
allows choice places, when we introduce our approach, we still adopt
the conflict-free option because of the following reasons:
1. Less Computation Complexity . Allowing arbitrary combina-
tion of choices among branches will increase the computation
complexity from O( m n ) to O[(2 m )
], that is, O(2 mn ).
2. Compactness and Intuitiveness to Users . When each choice
place selects multiple branches, many meaningless solutions
will result. For example, in the AOPS example in Section 3.5, if
we allow choice places, then the RSN (see the upmost net in
Figure 3.11) itself is a candidate solution, but obviously, this net
is an undesired one.
n
Although the candidate solutions generated by the conflict-freeness
constraint do not contain loop and choice (again, it may contain choice
over subtypes of data), they offer the “backbones” that can be further
refined (e.g., by adding choice branches or loop) by users. This
assumption is realistic since (1) choice branches occur in different
candidate solutions we give and it is easy to combine them; (2) as for
a choice or loop, which branches to select and the start/termination of
looping is beyond the scope that can be handled from services'
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