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

Chapter 4. Service Oriented Architecture 964.6.2 SOA– The target architectureThe target architecture (see figure 4.4) is expressed using identified SOA architecturalpatterns and relations between them. Motivation behind location ofparticular patterns the target architecture is following:1. Schema – is an XML document which describes vocabulary to express businessdata [82]. The schema is divided into domains. The reason why eachlayer depends on the schema is that each information in the system has tobe described according to the schema, consequently each service includes apart of the schema layer.2. Policy – provides a model and a syntax to describe and communicate policies[13]. The policies are defined in one place and as the schemas are applied toparticular services, therefore each layer has to have an access to the policies.3. Frontend – contains service clients therefore it is a top layer. Frontends maycommunicate with UI–Mediator if continuous feedback to user is required.This layer does not exist in patterns presented by T.Erl[32] but legacysystems have some user interface that also have to be migrated.4. Endpoints Layer – contains entry point for each inventory of basic services.If a service from other inventory or a client application wants to consumea service then the consumption has to be conducted via an endpoint. Endpointsdefine also possible operations therefore they serve also as Facade.5. Process Abstraction – consists of process services. Process services dependson basic services.6. Basic Services consist of services that provided by Entity Abstraction(Entity),Utility Abstraction(Utility), Rules Centralisation(Rules), Canonical Resource(Resources)and State Repository(State). Names in round brackets correspond to namesin figure.4.7 Benefits of SOASOA requires many experienced specialists including architects, programmers,requirement engineers and project managers. SOA requires also a lot of timewhat does not support well projects with a short time-to-market. NeverthelessService Oriented Architecture is introduced to companies that operate on a varietyof business domains including banking [46](Halifax Bank Of Scotland), post