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

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Chapter 4. <strong>Service</strong> <strong>Oriented</strong> Architecture 771. Accepts information requests from service requesters.2. Consults a metadata registry <strong>to</strong> determine how <strong>to</strong> assemble the requestedinformation using known data services.3. Retrieves the data from one or more data service providers.4. Applies data transform rules using a data transformation service that removesduplicate data and converts the data that have been collected in<strong>to</strong>the format specified by the service contract.5. Returns the results <strong>to</strong> the service requester.Frontend —corresponds <strong>to</strong> an upper layer <strong>of</strong> a traditional application likeWeb page or a rich client[46]. Frontends are used <strong>to</strong> initialize a process and retrievea result. The initiation does not have <strong>to</strong> be invoked by end user. It canbe a long living process which invokes specific events in some circumstances likeperiodical events.4.2.2 Other elementsThe definition <strong>of</strong> SOA[46] does not mention about one more element <strong>of</strong> <strong>Service</strong><strong>Oriented</strong> Architecture, namely <strong>Service</strong> Inven<strong>to</strong>ry. This element is not obliga<strong>to</strong>rybut it simplifies maintenance <strong>of</strong> large amount <strong>of</strong> services.<strong>Service</strong> Inven<strong>to</strong>ry [31] [46] – inven<strong>to</strong>ry is an independent element <strong>of</strong> thearchitecture and independently manages collection <strong>of</strong> services. The collectionscontain services important from point <strong>of</strong> view <strong>of</strong> the company.4.2.3 Types <strong>of</strong> services<strong>Service</strong>s can be divided in<strong>to</strong> following groups:1. Application Frontend – in general it does not have <strong>to</strong> be a service in terms<strong>of</strong> previously stated definition - it is rather a client <strong>of</strong> an application butit can also be other services like services from other company or a batchservice executing tasks periodically [46] .2. Basic <strong>Service</strong>[46] [31] – represents basic and stateless element <strong>of</strong> a domain.A basic service can be Data Centric <strong>Service</strong> or Logic Centric <strong>Service</strong>s.(a) Data Centric <strong>Service</strong>s – are responsible for maintaining only one maindata entity. The maintenance does not mean that a service executesonly CRUD operations - a service has <strong>to</strong> care also about locking mechanismand transactional management. To fulfill all his responsibilities,the service has <strong>to</strong> maintain database connection.

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