Miras bilgi sistemlerinin ilgiye-yönelik geliştirimi

ABSTRACTASPECT-ORIENTED EVOLUTION OF LEGACYINFORMATION SYSTEMSYasemin SatıroğlugM.S. in Computer EngineeringSupervisor: Prof. Dr. H. Altay GüveniruAugust, 2004A legacy information system is an old system that typically has been developedseveral years ago, and remains in operation within an organization. Since the soft-ware requirements change, legacy systems must be evolved accordingly. Variousapproaches such as wrapping, migration and redevelopment have been proposedto maintain legacy information systems. Unfortunately, these approaches havenot explicitly considered the concerns that are difficult to capture in single com-ponents, and tend to crosscut many components. Examples of such crosscuttingconcerns include distribution, synchronization, persistence, security, logging andreal-time behavior. The crosscutting property of concerns seriously complicatesthe maintenance of legacy systems because the code of the system needs to bechanged at multiple places, and conventional maintenance techniques fall shortto do this effectively.Aspect-Oriented Software Development (AOSD) provides explicit mechanismsfor coping with these crosscutting concerns. However, current AOSD approacheshave primarily focused on coping with crosscutting concerns in software systemsthat are developed from scratch. Hereby, the crosscutting concerns are imple-mented as aspects at the beginning, hence localized in single modules. In thisway the implementation and maintenance of crosscutting concerns can be pre-pared to a large extent so that the maintenance of these systems will be easierlater on. Unfortunately, legacy systems impose harsher requirements, becausecrosscutting concerns in legacy systems are neither explicitly identified nor havebeen prepared before.We provide a systematic process for analyzing the impact of crosscutting con-cerns on legacy systems. The process, which is called Aspectual Legacy AnalysisProcess (ALAP), consists of three sub-processes, Feasibility Analysis, AspectualiiiivAnalysis and Maintenance Analysis. All the three sub-processes consist of a set ofheuristic rules and the corresponding control. Feasibility Analysis, which consistsof two phases, describes rules for categorizing legacy systems, in the first phase;and describes the rules for evaluating legacy systems with respect to the abilityto implement static crosscutting and ability to implement dynamic crosscutting,in the second phase. The rules of the first phase are based on the categories oflegacy systems that we have defined after a thorough study to legacy informationsystems, and the rules of the second phase are based on our discussion of thesecategories with respect to crosscutting implementation. Once the legacy systemhas been categorized and evaluated with respect to crosscutting implementation,the Aspectual Analysis sub-process describes rules for identifying and specifyingaspects in legacy systems. Based on the results of the Feasibility Analysis andAspectual Analysis sub-processes, the Maintenance Analysis describes the rulesfor the selection of the appropriate legacy maintenance approach.ALAP has been implemented in the Aspectual Legacy Analysis Tool (ALAT),which implements the rules of the three sub-processes and as such helps to sup-port the legacy maintainer in analyzing the legacy system and identifying theappropriate maintenance approach.Keywords: Legacy Information Systems, Aspect-Oriented Software Development,Heuristic Rule Modelling.