Migration of a Chosen Architectural Pattern to Service Oriented ...

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Chapter 4. Service Oriented Architecture 84Service Realisation – When services are identified and specified, they have tobe realized. However, realization of a particular service is the final activity; it hasto be avoided when it is possible. This may sound strange or irrational, but it isfully justified. Realisation should be avoided because of reusability. Reusabilityprohibits development of a new service where an existing service can be reused.A new service is needed only when there is no existing service that can performrequired operation. This new service can be build from previously separatedreusable components if there is such possibility or it can be implemented fromscratch.4.4 SOA – architectural point of viewOverview of Architecture of SOA can be presented on three levels of complexity.(see figure 4.2).Each level consists of several layers of abstraction [46].4.4.1 Fundamental SOAFundamental SOA is the first and the most abstract level. It distinguishes onlyEnterprise and Basic layers [46]. Those two layers are sufficient to provide basicSOA functionality. Enterprise layer contains application frontends (clients)(see 4.2.3 for more information about frontends ). Frontends provide access tothe application itself. Basic layer contains basic services (see 4.2.3 for more informationabout basic services ). The structure built on only two layers mayappear to be insufficient, but it is sufficient to provide basic functionality and itis a good starting point for further development of more elaborated and complexstructure. Due to clear separation of clients from basic services, the architecturesupports maintain activities and, in a long run prevents data redundancy. Theredundancy may exist when a company converts existing application into ServiceOriented Architecture.4.4.2 Networked SOAFundamental SOA may be sufficient for small projects but it is hard to maintainwhen a project grows in scope or when an application has to be integrated withanother system. Networked SOAis an upgraded version of Fundamental SOA[46]. The upgrade relies on introduction of one additional layer-Intermediarylayer. This additional layer is placed between Basic and Enterprise layer and ismeant to provide mechanisms facilitating technical and conceptual integrationby introducing Intermediary Services. Those services serve as gateways, facadesand adapters. The names of services of Intermediary Layer derive from designpatterns and behavior of those services correspond the patterns. The role ofparticular types of services is following:
Chapter 4. Service Oriented Architecture 851. Adapter – plays a role of message converter. An adapter service receives amessage in one format and transforms it to another format. Adapters havevery strict role what in turn reduces their potential reuse in both currentand other project.2. Facade – hides underlying complexity and provides unified API which supportsusage of underlying basic services. A goo d example is facade utilizationto hide operation on distributed databases [46].The unified API servesalso as a view, which clarifies usage of a part of the system by hiding unnecessary(from service customer point of view) functionality. This type ofservice serves as an additional layer of abstraction. This reduces reusabilityof the service. Consequently, Facade is rather project scope service andshould be considered in this way.3. Gateway –Gateway or Technology Gateway is a kind of an additional interface,which in opposite to a traditional interface (like interface in programminglanguage) serves as an interface between two different technologies. Atfirst glance, it seems that Gateways are unnecessary or redundant especiallywhen the application is designed from scratch. This is not true because SOAby definition assumes usage of different technologies from different vendors.Taking advantage of Gateways removes the need of introduction of old technologyto new system while the new system is integrated with legacy system.As a result, Gateway simplifies achieving of technology independence.4.4.3 Process–Enabled SOAThe last and the most complex SOA structure is Process Enabled SOA [46]. Infact it is just an enriched version of Networked SOA. The difference between thosetwo versions is that Process Enabled SOA has forth –Process –layer. The layercontains only Process Centric Services which are in one respect very special. ProcessCentric Services are not stateless as the others are. They manage the state inorder to handle long living processes or to share the state between services. Thisis especially important when an application uses asynchronous communication.Utilising of Process Centric Services lighten Application Frontends and bringsthem to role of User Interface, what increases cohesion of single services.
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Master ThesisSoftware EngineeringTh
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List of Figures1.1 Research methodo
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List of Tables3.1 Summary of archit
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Chapter 1Introduction1.1 Background
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Chapter 1. Introduction 3technique
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Chapter 1. Introduction 5was notice
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Chapter 1. Introduction 7do not pro
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Chapter 1. Introduction 9Chapter 4
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Chapter 2. Related Work 11This chap
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Chapter 2. Related Work 15Figure 2.
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Chapter 2. Related Work 17Drawbacks
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Chapter 2. Related Work 19Figure 2.
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Chapter 2. Related Work 21Advantage
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Chapter 2. Related Work 23between a
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Chapter 2. Related Work 252. Applic
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Chapter 3. Architectural Patterns 3
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Chapter 5. Guidelines 135Output: Du
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Chapter 5. Guidelines 137generation
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Chapter 5. Guidelines 139(a) Fronte
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Chapter 5. Guidelines 141Figure 5.1
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Chapter 5. Guidelines 143Figure 5.1
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Chapter 5. Guidelines 145FrontendSc
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Chapter 6. Conclusion 147There are
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Chapter 6. Conclusion 149RQ.6 How t
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References[1] http://www.soa-manife
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References 153[22] Frank Buschmann,
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References 155[46] Dirk Krafzig, Ka
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References 157[67] Xiaohong Qiu. Bu
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