12.07.2015 Views

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 ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Chapter 2Related WorkMotivation behind migration is a result <strong>of</strong> two fac<strong>to</strong>rs. The first fac<strong>to</strong>r is the factthat old but very <strong>of</strong>ten mission critical systems cannot be developed or maintainedanymore because it becomes <strong>to</strong>o expensive. This fac<strong>to</strong>r is called [74]“Legacy Systemdilema”. The second fac<strong>to</strong>r describes why a company does not want <strong>to</strong>develop a new application from the scratch. This may include for instance lack<strong>of</strong> documentation <strong>of</strong> the system. Additionally, the system can be a mature applicationthat is a result <strong>of</strong> many years <strong>of</strong> development and maintenance. When acompany decides <strong>to</strong> migrate an application, it always has <strong>to</strong> face two very generalproblems [74]. The first problem is caused by own, old application which wasdeveloped for years and may be lacking in documentation. The second problemis a target system, namely the architecture and migration decision that are associatedwith selection <strong>of</strong> the target system.One <strong>of</strong> possible migration directions is migration <strong>to</strong>ward <strong>Service</strong> <strong>Oriented</strong> Architecturewhich brings some very promising benefits like code reuse and easyfurther integration (see 4.7).But even if the choice is made, still an open questionremains: How <strong>to</strong> conduct the migration? According <strong>to</strong> Z.Zhang and H.Yangthere are three types <strong>of</strong> migration <strong>to</strong>ward SOA [84].The first approach calledWhite–Box requires high understanding <strong>of</strong> the system and allows <strong>to</strong> make significantchanges in code if there is such need. The second approach is focusedrather on input and output <strong>of</strong> the system and is called Black–Box. The thirdapproach lies between white and Black–Box techniques and it is called Grey–Boxtechnique. The ”Gray–Box” technique includes code analysis, modification <strong>of</strong> thecode and analysis <strong>of</strong> behaviour <strong>of</strong> the system as a whole entity.How does migration is important is also evidenced by the fact that it becamea subject <strong>of</strong> standardisation. The standard, named <strong>Architectural</strong>–DrivenModernisation (ADM) is meant <strong>to</strong> facilitate migration efforts[58]. This standardconsiders system on three levels <strong>of</strong> abstraction. The standard investigates alsorole <strong>of</strong> patterns in the system. <strong>Migration</strong> <strong>to</strong>wards <strong>Service</strong> <strong>Oriented</strong> Architecturebecame also a subject <strong>of</strong> interest <strong>of</strong> architects dealing with non–SOA architecturalpatterns like patterns identified in the second chapter.10

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!