Modularization and Specification of Service-Oriented Systems Modularization and Specification of Service-Oriented Systems Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus Prof. K. C. A. M. Luyben voorzitter van het College voor Promoties, in het openbaar te verdedigen op dinsdag 5 juli om 15:00 uur door Linda Iris TERLOUW ingenieur in de technische informatica en bedrijfsinformatietechnologie geboren te Tilburg Dit proefschrift is goedgekeurd door de promotor: Prof. dr. ir. J. L. G. Dietz Samenstelling promotiecommissie: Rector magnificus, Technische Universiteit Delft, voorzitter Prof. dr. ir. J. L. G. Dietz, Technische Universiteit Delft, promotor Prof. dr. ir. A. Verbraeck, Technische Universiteit Delft Prof. dr. R. J. Wieringa, Universiteit Twente Prof. dr. J. Verelst, Universiteit van Antwerpen Prof. dr. ing. J. B. F. Mulder MBA, Universiteit van Antwerpen Prof. dr. H. A. Proper, Radboud Universiteit Nijmegen Dr. dipl.-ing. A. Albani, Universiteit van St. Gallen Prof. dr. Y. H. Tan, Technische Universiteit Delft, reservelid Verspreid door: Linda Terlouw Martinus Nijhoffhove 2 3437 ZR Nieuwegein Nederland [email protected] ISBN: 978-94-6108-182-7 SIKS Dissertatiereeks nr. 2011-21 Het in dit proefschrift vermelde onderzoek is uitgevoerd onder de auspici¨en van SIKS, de Nederlandse School voor Informatie- en KennisSystemen. Druk: Gildeprint Drukkerijen - Enschede Omslagontwerp: Jeroen Advocaat Gezet in LATEX, diagrammen in OmniGraffle 2011 Linda Terlouw. Alle rechten voorbehouden. Acknowledgments Pursuing a PhD is a painful, yet rewarding experience. Every PhD student and promotor will confirm that the only good dissertation is a done disser- tation. After six years of research I am happy to present the final results. The research is conducted at the Delft University of Technology in a research group consisting of hybrids; people who work in industry with an academic interest and people who work in academia with a wish to put theory into practice. Combining research with a `day job' as IT consultant is a drawback as well as a benefit. The drawback is the chronic lack of time and focus. The benefit is a continuous reality check on the relevance of the research. Though writing a dissertation seems like a very lonely process, many peo- ple in fact contributed to it. First of all, I thank my promotor Jan Dietz, who guided me through the jungle of academic research. My daily supervisor, Antonia Albani, taught me the very specific writing style used in academic papers and gave valuable feedback on my draft papers that helped in get- ting the papers accepted. Also, I would like to express my gratitude to the other members of my dissertation committee for reading the dissertation and providing feedback. The CIAO! doctoral consortia gave me an opportunity to present my work in an early phase to the CIAO! board members and the fellow doctoral stu- dents. Presenting at such an event was never easy; interruptions started at the first slide and razor-sharp comments were made by the board members. But these events contributed highly to the selection of an appropriate research topic and to building the research on strong theoretical foundations. In this dissertation three case studies are presented. I would like to thank the case study participants at the Port of Rotterdam, De Lage Landen and Air France/KLM for giving me the opportunity to validate my findings in practice and for providing valuable new insights. Especially, I would like to v thank the persons who took the time and effort to arrange the interviews and workshops: Edwin de Werk and Kees Eveleens Maarse (Port of Rotterdam), Rens Voogt (De Lage Landen), and Frank Rappange (Air France/KLM). TeamSupport supported these case studies by providing a license for group decision support software. I would like to express my appreciation to Paul Weghorst, Reggie Maas- Schellekens, and Eric van der Ende who supported my PhD research when I was working at Ordina. Furthermore, I am grateful to all the members of the former SOA Focus Team of Ordina for all the interesting discussions. Thanks Bart Pruijn, Art Ligthart, Jan-Willem Hubbers, Marco Brattinga, Willem van Pruijssen, Hermen Grievink, and Lex Haket. For giving tips and tricks on how to combine life as a PhD student and an entrepreneur I would like to thank Wiebe Hordijk. My parents always supported me in my academic activities and encouraged me to bring out my best. I owe my career as an IT consultant as well as my (just-starting) academic career to them. Also, I would like to thank my brother Joeri with whom I had the pleasure of writing a brother-sister paper. Finally, I would like to thank my husband Andr´efor standing by me at all times during this PhD process and for accepting the consequences of PhD research in terms of time and attention. Linda Terlouw, 2011 vi Summary Modularization and Specification of Service-Oriented Systems Rationale and Objective Modern day enterprises face a dilemma. On the one hand they want to be able to respond rapidly to market changes, i.e. they want to be agile. On the other hand they want (or actually need) to introduce complexity in their orga- nization because of strategic choices like the mass-customization of products and services, the introduction of more complex products and services, and the participation in interorganizational networks. For example, getting an overview of their business processes and their supporting software systems is quite a challenge due to their sheer size and their interwoven structure. An even bigger problem is that `the rules' for designing enterprises are still ill-understood or at least ill-documented. In general systems theory modularity is proposed as a means for dealing with complexity. The objective we wanted to achieve through this disserta- tion is to provide practitioners with a better understanding of how to deal with modularity of enterprises and their supporting software systems by ap- plying service-orientation. Currently, most practitioners (usually enterprise architects) make decisions based on gut feeling and experience. Our intention was to make this design knowledge more fundamental and explicit. We based our research on literature from the field of software engineering as well as from the organizational sciences. vii First, we sought to find criteria for decomposing service-oriented systems into coarse-grained modules. These modules can comprise humans and/or software systems. So we did not focus on how to structure a single software system, but we focused on how to structure the complete set of services of an enterprise. Advantages of introducing this modularity are, among others, making the total enterprise more comprehensible and minimizing the effect that changes in one module may have on other modules. To minimize interde- pendencies between modules it is important to take into account the principle of `maximum cohesion and minimal coupling'. This led to the question how we can conform to this maximum cohesion and minimal coupling principle. And are any other criteria important for module identification? Moreover, are these criteria only software engineering principles or maybe (also) organiza- tional criteria? We answered these questions in our `laboratory', i.e. real-life, large organizations with complex IT environments. Second, we saw that current service specification approaches are very im- mature. This poses a problem, because confusion arises when parties have different interpretations of each other's syntax, semantics, or responsibili- ties. For example, providers and consumers will not be able to exchange any useful information if one party only speaks English (or XML) and the other only Dutch (or EDIFACT). Also, problems can occur when the provider thinks the height of a product is in centimeters while the consumer specifies height in inches. Or maybe provider and consumer do not call the same side of a product `height', because it can be positioned on the floor in different ways. Another type of problem comes into life when the consumer expects the provider to deliver a product at the highest possible quality level while the provider actually delivers the cheapest, low-quality product. To structure the information about a service we wanted to design a specification framework. This framework supports the provider in describing his services by stating what aspects need to be specified to enable the service consumer to find the service, to access it, and to judge whether or not the service meets his re- quirements. We derived the framework from the Ψ-theory, in order to base it on appropriate scientific foundations. Summarizing, we aimed at two things: (i) to formulate criteria for delim- iting coarse-grained modules of a service-oriented system and (ii) to design a framework for specifying services. viii Research Approach For the design of the service specification framework we followed the design science research methodology. The theoretical part of our research is based on the notions of Enterprise Ontology and Enterprise Architecture, as adopted by the Enterprise Engineering community (www.ciaonetwork.org). We designed a service specification framework based on the Ψ-theory, the theory that un- derlies the notion of Enterprise Ontology. The Generic System Development Process (GSDP), which clarifies the notion of architecture, gives guidance in the design process by proposing a clear and consistent terminology. We specialized the GSDP for service-orientation, the most recent paradigm for information system modularity. Subsequently, we verified whether practition- ers agree that the service specification framework is complete and that it does not contain irrelevant aspects. In our case studies we used semi-structured interviews, because written questionnaires about complex matters are often not filled in very thoughtfully (`just get it done with'). Also, we do not want to structure the interviews completely to give the interviewees the chance to elaborate on what they think is important.