![](bg6.png)
same process step when computing solutions for
different execution paths.
7 CONCLUSION AND OUTLOOK
In highly competitive markets, flexible and efficient
business process execution is indispensable. Follow-
ing the paradigm of SOA, using services from (ex-
ternal) service providers (probably having large ex-
pertise in a certain business field), enables a flexible
and efficient process execution. In case, multiple
service providers offer (quite) equivalent services at
different quality and cost levels on various service
marketplaces (as is probably the case in the Internet
of Services), enterprises have the opportunity to de-
cide which services from which service providers to
select accomplishing the required functionalities
based on their QoS preferences, increasing the
achieved efficiency regarding the business process
execution.
Therefore, the service-selection-problem for
complex workflows is addressed in my research. In
this context, I contributed or contribute the follow-
ing:
An approach for aggregating QoS values for
(combinations of) complex workflow patterns.
An approach for solving the service-selection-
problem optimally (if an optimal solution ex-
ists) without preliminary identifying all execu-
tion paths.
A heuristic algorithm for a nearly optimal solu-
tion of the service-selection-problem due to
scalability issues considering the optimal solu-
tion.
A concept for a quantification of qualitative
service properties in order to integrate security
into the service selection decision.
A re-planning strategy to react upon positive
and negative SLA deviations for complex
workflows.
In particular, the integration of further complex
workflow patterns as multi-choice (OR-split) and
multi-merge (OR-join) into the optimization prob-
lem – yet insufficiently considered (even in the men-
tioned heuristic approaches) in the literature – and
the development of a reasonable concept for quanti-
fication of security is currently investigated. The
extension of the re-planning mechanism for complex
workflows in combination with the progression of
the semantic matchmaker (and the therefore required
semantic annotations) is addressed as well in my
future research.
ACKNOWLEDGEMENTS
This work is supported in part by the E-Finance Lab
e. V., Frankfurt am Main, Germany
(http://www.efinancelab.com).
REFERENCES
Van der Aalst, W., Ter Hofstede, A., Kiepuszewski, B.,
Barros, A., 2003. Workflow Patterns, Distributed Pa-
rallel Databases, 14, 1, pp. 5-51.
Anselmi, J., Ardagna, D., Cremonesi, P., 2007. A QoS-
based Selection Approach of Autonomic Grid Servic-
es. In International Conference on Service-oriented
Computing. Vienna, Austria.
Ardagna, D., Pernici, B., 2007. Adaptive Service Composi-
tion in Flexible Processes, Transactions on Software
Engineering, 33, 6, pp. 369-384.
Domschke, W., Drexl, A., 2007. Einführung in Operations
Research, Springer Verlag. Heidelberg.
Heckmann, O., 2004. A System-oriented Approach to Effi-
ciency and Quality of Service for Internet Service Pro-
viders, PhD thesis. TU Darmstadt, Fachbereich Infor-
matik.
Huang, A., Lan, C.-W., Yang, S., 2009. An optimal QoS-
based Web service selection scheme, Information Sci-
ences, 179, pp. 3309-3322.
Jaeger, M., Rojec-Goldmann, G., 2005. SENECA-
Simulation of Algorithms for Selection of Web Ser-
vices for Composition. In Technologies for E-Services.
Trondheim, Norway.
Jaquith, A., 2007. Security Metrics: Replacing Fear, Un-
certainty, and Doubt, Addison-Wesley Professional.
Krafzig, D., Banke, K., Slama, D., 2004. Enterprise SOA:
Service-Oriented Architecture Best Practices, Prentice
Hall PTR. New Jersey, USA.
Leymann, F., Roller, D., 2000. Production Workflow:
Concepts and Techniques, Prentice Hall PTR. New
Jersey, USA.
Mabrouk, N., Georgantas, N., Issarny, V., 2009. A Seman-
tic End-to-End QoS Model for Dynamic Service-
oriented Environments. In Principles of Engineering
Service Oriented Systems. Vancouver, Canada.
Menascé, D., Casalicchio, E., Dubey, V., 2008. A Heuris-
tic Approach to optimal Service Selection in Service-
oriented Architectures. In Workshop on Software and
Performance. New Jersey, USA.
Miede, A., Nedyalkov, N., Schuller, D., Repp, N.,
Steinmetz, R., 2009. Cross-organizational Security –
The Service-oriented Difference. In International Con-
ference on Service-Oriented Computing (ICSOC 2009
Workshops). Stockholm, Sweden.
Schuller, D., Papageorgiou, A., Schulte, S., Eckert, J.,
Repp, N., Steinmetz, R., 2009. Process Reliability in
Service-oriented Architectures. In Digital Ecosystems
and Technologies. Istanbul, Turkey.
Schuller, D., 2010. Sichere und Zuverlässige
Prozessausführung in Serviceorientierten
OPTIMIZING QOS-BASED SERVICE SELECTION IN SERVICE-ORIENTED ARCHITECTURES
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