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

Chapter 4. Service Oriented Architecture 764.2 Elements of SOAThis section describes briefly elements of service oriented architecture.1. Main elements – This section focuses on elements presented in the defitionprovided by Krafzig[47].2. Other elements – The second section presents other elements of SOA thatare not mentioned in the definition but they were identified during researches.3. Types of Services – While the first section describes the idea behind services,this section presents briefly types of services.4. Structure of a service – this section presents structure of a service4.2.1 Main elementsService — derives from business context of an organisation. Service can bedescribed as [59] “an asset that corresponds to real–world business activities orrecognisable business functions.” Service does not only provide functionality, italso consumes or consumes and provides functionality. A service should be discoverable(available through discovery mechanism like for instance service registry)and bound in run-time, however static bound is also possible . A service can bealso be characterized by some properties [42] ] such as performance, capacity, andreliability. Service is a complex entity and consists of Service Contract, Interfaceand Implementation [46].Service repository [46][31] —contains descriptions of services and providesall information required to access them. The information includes localization,provider, technical constrains, terms of usage, fees, service subscription and userregistration if the services are public. Repositories can be stored in databases tostore contract of descriptions for each service version. The database may storecontracts, description of each version of a service and some administrative data.The term repository is also interchanged in literature with registry. In fact bothterms are very similar and differ only in one aspect. Repository is a term usedduring design time, while registry is associated with runtime usage [31]Enterprise Service bus — Service Bus is also referred as Enterprise ServiceBus (ESB). The bus is a middleware concept that enables interaction betweendifferent applications [25].(Enterprise) Service Bus can be implemented as forinstance Enterprise Application Integration middleware [25] [13], brokering technology[13] or a platform specific component like WebShare application Server[13] [60]. In fact, ESB is a communication mechanism that performs followingactivities [59]: