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

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Chapter 5. Guidelines 120How to: Reduces memory load of a stateful service by deferring their statesto a specially designed repositories like databases. State deferring requiresadditional effort related to memory load controlling as well as state storingand recovering, but it may occur crucial for performance. Access to deferringmechanism should be enabled via Canonical Resource [32]. Literatureprovides two possible ways for state deferring. First, (Partial State Deferral)describes storing of state of services in databases, while second (ServiceGrid) introduces Grids - an alternative for database state storage(a) Partial State Deferral [32]assumes deferring of only a part of the service’sstate. The deferred state will be no longer used in the process.Implementation of State deferring mechanisms should be consideredwhen all the processes are identified (see figure 5.11) This will allowthe process service to remain statefull and reduce memory load in thesame time. In order to fully leverage state deferring pattern, parts ofthe process that uses the same data should be executed in a sequenceif it is possible. For instance a process invokes firstly only servicesmanipulating on one part of a message, then a partial result is storedin database and process manipulates the next part of the message.(b) Service Grid [32]proposes an alternative for state storage. In oppositeto a typical database-based, Service Grid proposes state storage in aspecial dedicated grid of services. The grid contains many services thatare synchronized in order to provide security. Besides all the benefitsrelated to state deferring and alternative storage solution, Service Gridhas one significant drawback. It is vendor dependent. Grid has to beintegrated with SOA infrastructure - typically infrastructure providedby vendor of the grid.Introduction of State Deferring mechanism is always associated with performancereduction, thereupon the pros and cons of the mechanism should becarefully considered. Nevertheless application of State Repository may payoff when a process is very long or asynchronous. In case of asynchronousprocesses, final states can be stored and returned once (a few results) insteadof a few single returns.12. Identify current points of access to the migrated systemApplied SOA pattern: FrontendsHow to: Available literature presents this part of migration as a complexactivity that is not limited only to “separate clients” task. According to[2],Presentation Layer is a complex entity that is broken into three separatedelements:
Chapter 5. Guidelines 121ViewViewProcess AbstractionProcess AbstractionInventory EndpointsInventory EndpointsSchemaPolicySchemaBasic ServicesPolicyBasic ServicesUtility+ State Repository =UtilityResourcesResourcesEntityEntityRulesRulesStateFigure 5.11: Migration step 11(a) Presentation Service Provider – in opposite to ordinary service, presentationprovider does not provide business functionality. The serviceprovides presentation components that can be further integrated withuser interface. The components are also connected to correspondingbusiness services.(b) Presentation Service Consumer – invokes Presentation Service Providersand uses provided presentation components to create a complex UserInterface (UI). If elements of UI are coherent, a user is not even awarethat different parts of the screen derive from different applications.(c) Presentation Service Registry – registers Presentation Service Providersand provides all the information as previously described Service Repositorydoes.There is also SOAUI Composition Framework [81] supporting creation ofPresentation Layer that covers GUI in similar scope. However the solutiongives additional reusability on potentially not reusable abstraction level,it requires additional effort associated with introduction of the framework.Application of the framework reduces also performance of application whatis an implication of additional layers of abstraction. Application of thisrelatively heavy presentation is fully justified in the field of large businessapplication where UI-related user experience can be a major evaluationfactor [81]. In case of MVC, frontends are migrated from View (see figure5.12).13. Identify all the places in user interface where a continuous feedback fromapplication to end user is provided
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