Migration of a Chosen Architectural Pattern to Service Oriented ...
Migration of a Chosen Architectural Pattern to Service Oriented ...
Migration of a Chosen Architectural Pattern to Service Oriented ...
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Chapter 2. Related Work 17Drawbacks1. Application <strong>of</strong> the technique requires a lot <strong>of</strong> time2. The technique is heavy. It produces a lot <strong>of</strong> documents3. The technique does not consider properties <strong>of</strong> architecture <strong>of</strong> migrated system2.1.3 Black–Box: WrappingIn opposite <strong>to</strong> White–Box technique, Black–Box technique does not affect thecode <strong>of</strong> the migrated system. The system is considered as a whole entity andanalysis <strong>of</strong> a legacy system is limited only <strong>to</strong> analysis <strong>of</strong> inputs and outputs. Thissection presents briefly an overview <strong>of</strong> an example <strong>of</strong> a Black–Box technique,namely Wrapping [23].The description presents two parts <strong>of</strong> the approach. Thefirst part describes basic elements. The second presents main processesElementsWrapping technique consists <strong>of</strong> several element that work on Finite State Au<strong>to</strong>mationand legacy screens. See picture 2.2 for wrapper schema. The elementsare following:Terminal emula<strong>to</strong>r – replaces server terminal that normally has an access <strong>to</strong>the legacy system and transfers requests from a GUI based application or requestscalled via legacy system’s API. In other words, terminal emula<strong>to</strong>r provides aninterface <strong>to</strong> access legacy functionality. The implementation depends <strong>of</strong> terminaltype. There are two main types <strong>of</strong> terminals [23]:1. Stream <strong>Oriented</strong> Terminal –communicates with the system via two–directionalchannel. The terminal sends data just after they are typed. Received dataare computed by the legacy system and send back as a screen representedby a matrix <strong>of</strong> characters.2. Block <strong>Oriented</strong> Terminal –in opposite <strong>to</strong> stream terminal, Block <strong>Oriented</strong>Terminal uses screens represented by a set <strong>of</strong> fields with their localisation.The legacy system computes the result and sends back a screen containinga new set <strong>of</strong> fields with corresponding localisations.States identifier – Given an input and a start state, the system can reach afinite amount <strong>of</strong> states. Each state has own screen that is returned by the systemas an output. The responsibility <strong>of</strong> State Identifier is <strong>to</strong> match Screen Template <strong>to</strong>the screen returned by the system. To increase matching probability, the legacyscreen should be described by the biggest possible amount <strong>of</strong> data that can beobtained using reverse engineering on the legacy screen.
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