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Software Maintenance Maintenance Is Inevitable Types of Maintenance SoftWindows 8/18/2003 Software Maintenance • Managing the processes of system change Reverse Engineering (Software Maintenance & Reengineering) © SERG Maintenance is Inevitable • The system requirements are likely to change while the system is being developed because the environment is changing. • When a system is installed in an environment it changes that environment and therefore changes the system requirements. Reverse Engineering (Software Maintenance & Reengineering) © SERG Types of Maintenance • Perfective maintenance – Changing a system to make it meet its requirements more effectively. • Adaptive maintenance – Changing a system to meet new requirements. • Corrective maintenance – Changing a system to correct deficiencies in the way meets its requirements. Reverse Engineering (Software Maintenance & Reengineering) © SERG Distributed Objects 1 SoftWindows 8/18/2003 Distribution of Maintenance Effort Corrective maintenance (17%) Adaptive maintenance Perfective (18%) maintenance (65%) Reverse Engineering (Software Maintenance & Reengineering) © SERG Evolving Systems • It is usually more expensive to add functionality after a system has been developed rather than design this into the system: – Maintenance staff are often inexperienced and unfamiliar with the application domain. – Programs may be poorly structured and hard to understand. – Changes may introduce new faults as the complexity of the system makes impact assessment difficult. – The structure may be degraded due to continual change. – There may be no documentation available to describe the program. Reverse Engineering (Software Maintenance & Reengineering) © SERG The Maintenance Process • Maintenance is triggered by change requests from customers or marketing requirements. • Changes are normally batched and implemented in a new release of the system. • Programs sometimes need to be repaired without a complete process iteration but this is dangerous as it leads to documentation and programs getting out of step. Reverse Engineering (Software Maintenance & Reengineering) © SERG Distributed Objects 2 SoftWindows 8/18/2003 System Documentation • Requirements document • System architecture description • Program design documentation • Source code listings • Test plans and validation reports • System maintenance guide Reverse Engineering (Software Maintenance & Reengineering) © SERG Maintenance Costs • Usually greater than development costs (2* to 100* depending on the application). • Affected by both technical and non- technical factors. • Maintenance corrupts the software structure so makes further maintenance more difficult. • Aging software can have high support costs (e.g., old languages, compilers etc.) Reverse Engineering (Software Maintenance & Reengineering) © SERG Maintenance Cost Factors • Module independence – It should be possible to change one module without affecting others. • Programming language – High-level language programs are easier to maintain. • Programming style – Well-structured programs are easier to maintain. • Program validation and testing – Well-validated programs tend to require fewer changes due to corrective maintenance. Reverse Engineering (Software Maintenance & Reengineering) © SERG Distributed Objects 3 SoftWindows 8/18/2003 Maintenance Cost Factors (Cont’d) • Documentation – Good documentation makes programs easier to understand. • Configuration management – Good CM means that links between programs and their documentation are maintained. • Application domain – Maintenance is easier in mature and well-understood application domains. • Staff stability – Maintenance costs are reduced if the same staff are involved with them for some time. Reverse Engineering (Software Maintenance & Reengineering) © SERG Maintenance Cost Factors (Cont’d) • Program age – The older the program, the more expensive it is to maintain (usually) . • External environment – If a program is dependent on its external environment, it may have to be changed to reflect environmental changes. • Hardware stability – Programs designed for stable hardware will not require to change as the hardware changes. Reverse Engineering (Software Maintenance & Reengineering) © SERG Maintenance Measurements • Control complexity: – Can be measured by examining the conditional statements in the program. • Data complexity: – Complexity of data structures and component interfaces. • Length of identifier names: – Longer names imply readability. • Program comments: – Perhaps more comments mean easier maintenance. Reverse Engineering (Software Maintenance & Reengineering) © SERG Distributed Objects 4 SoftWindows 8/18/2003 Maintenance Measurements (Cont’d) • Coupling: – How much use is made of other components or data structures • Degree of user interaction: – The more user I/O, the more likely the component is to require change. • Speed and space requirements: – Require tricky programming, harder to maintain. Reverse Engineering (Software Maintenance & Reengineering) © SERG Process Measurements • Number of requests for corrective maintenance. • Average time taken to implement a change request. • Number of outstanding change requests. • If any or all of these is increasing, this may indicate a decline in maintainability. Reverse Engineering (Software Maintenance & Reengineering) © SERG Software Re-engineering • Reorganising and modifying existing software systems to make them more maintainable. Reverse Engineering (Software Maintenance & Reengineering) © SERG Distributed Objects 5 SoftWindows 8/18/2003 When to Re-engineer • When system changes are mostly confined to part of the system then re-engineer that part. • When hardware or software support becomes obsolete. • When tools to support re-structuring are available. Reverse Engineering (Software Maintenance & Reengineering) © SERG Re-engineering Advantages • Reduced risk – There is a high risk in new software development. • Reduced cost – The cost of re-engineering is often significantly less than the costs of developing new software. Reverse Engineering (Software Maintenance & Reengineering) © SERG Re-engineering Cost Factors • The quality of the software to be re- engineered. • The tool support available for re- engineering. • The extent of the data conversion which is required. • The availability of expert staff for re- engineering. Reverse Engineering (Software Maintenance & Reengineering) © SERG Distributed Objects 6 SoftWindows 8/18/2003 Source Code Translation • Involves converting the code from one language (or language version) to another e.g., FORTRAN to C • May be necessary because of: – Hardware platform update – Staff skill shortages – Organizational policy changes • Only realistic if an automatic translator is available. Reverse Engineering (Software Maintenance & Reengineering) © SERG Reverse Engineering • RE is the process of determining how a system works by analyzing its internal constituents and/or its external behavior. • In the software world one would say that RE is trying to figure out how a system works by: – Inspecting the source code and documentation (if it exists) – Exercising the executable programs and observing their behavior. Reverse Engineering (Software Maintenance & Reengineering) © SERG The Reverse Engineering Process Program stucture Automated diagrams analysis System System to be Document Data stucture information re-engineered generation diagrams store Manual annotation Traceability matrices Reverse Engineering (Software Maintenance & Reengineering) © SERG Distributed Objects 7 SoftWindows 8/18/2003 Reverse Engineering • Reverse engineering often precedes re- engineering but is sometimes worthwhile in its own right – The design and specification of a system may be reverse engineered so that they can be an input to the requirements specification process for the system’s replacement. – The design and specification may be reverse engineered to support program maintenance. Reverse Engineering (Software Maintenance & Reengineering) © SERG Why is RE Important to Software Developers? • Most software that is developed is not “from scratch”. • Understanding someone else’s source code, specifications, designs, is difficult. – Why is this so? – What makes software more difficult to understand than a toaster or a car? Reverse Engineering (Software Maintenance & Reengineering) © SERG Software Maintenance Problem • A company hires a bright software developer to maintain a system. • The project manager points the developer to a source code directory and says “become an expert in the system as soon as possible”. • The IBM Tobey back-end compiler project allowed for a 1 year learning curve (but this is quite rare). Reverse Engineering (Software Maintenance & Reengineering) © SERG Distributed Objects 8 SoftWindows 8/18/2003 Program Structure Improvement • Maintenance tends to corrupt the structure of a program. It becomes harder to understand. • The program may be automatically restructured to remove unconditional branches. • Conditions may be simplified to make them more readable. Reverse Engineering (Software Maintenance & Reengineering) © SERG Program Modularisation • The process of re-organising a program so that related program parts are collected together in a single module. • Usually a manual process that is carried out by program inspection and re-organisation. Reverse Engineering (Software Maintenance & Reengineering) © SERG Recovering Data Abstractions • Many legacy systems use shared tables and global data to save memory space. • This causes problems because changes have a wide impact in the system.
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