Software Evolution and Maintenance PDF

Software Evolution and maintenance Advanced Software Engineering 2024-2025 Topics covered Evolution processes Legacy systems Software maintenance Advanced Software Engineering 2024-2025 Software change Software change is inevitable...

Software Evolution and maintenance Advanced Software Engineering 2024-2025 Topics covered Evolution processes Legacy systems Software maintenance Advanced Software Engineering 2024-2025 Software change Software change is inevitable New requirements emerge when the software is used; The business environment changes; Errors must be repaired; New computers and equipment is added to the system; The performance or reliability of the system may have to be improved. A key problem for all organizations is implementing and managing change to their existing software systems. Advanced Software Engineering 2024-2025 Importance of evolution Organizations have huge investments in their software systems - they are critical business assets. To maintain the value of these assets to the business, they must be changed and updated. The majority of the software budget in large companies is devoted to changing and evolving existing software rather than developing new software. Advanced Software Engineering 2024-2025 A spiral model of development and evolution Advanced Software Engineering 2024-2025 Evolution and servicing Advanced Software Engineering 2024-2025 Evolution and servicing Evolution The stage in a software system’s life cycle where it is in operational use and is evolving as new requirements are proposed and implemented in the system. Servicing At this stage, the software remains useful but the only changes made are those required to keep it operational i.e. bug fixes and changes to reflect changes in the software’s environment. No new functionality is added. Phase-out The software may still be used but no further changes are made to it. Advanced Software Engineering 2024-2025  Evolution processes Advanced Software Engineering 2024-2025 Evolution processes Software evolution processes depend on The type of software being maintained; The development processes used; The skills and experience of the people involved. Proposals for change are the driver for system evolution. Should be linked with components that are affected by the change, thus allowing the cost and impact of the change to be estimated. Change identification and evolution continues throughout the system lifetime. Advanced Software Engineering 2024-2025 Change identification and evolution processes Advanced Software Engineering 2024-2025 The software evolution process Advanced Software Engineering 2024-2025 Change implementation Advanced Software Engineering 2024-2025 Change implementation Iteration of the development process where the revisions to the system are designed, implemented and tested. A critical difference is that the first stage of change implementation may involve program understanding, especially if the original system developers are not responsible for the change implementation. During the program understanding phase, you have to understand how the program is structured, how it delivers functionality and how the proposed change might affect the program. Advanced Software Engineering 2024-2025 Urgent change requests Urgent changes may have to be implemented without going through all stages of the software engineering process If a serious system fault has to be repaired to allow normal operation to continue; If changes to the system’s environment (e.g. an OS upgrade) have unexpected effects; If there are business changes that require a very rapid response (e.g. the release of a competing product). Advanced Software Engineering 2024-2025 The emergency repair process Advanced Software Engineering 2024-2025 Agile methods and evolution Agile methods are based on incremental development so the transition from development to evolution is a seamless one. Evolution is simply a continuation of the development process based on frequent system releases. Automated regression testing is particularly valuable when changes are made to a system. Changes may be expressed as additional user stories. Advanced Software Engineering 2024-2025 Handover problems Where the development team have used an agile approach but the evolution team is unfamiliar with agile methods and prefer a plan-based approach. The evolution team may expect detailed documentation to support evolution, and this is not produced in agile processes. Where a plan-based approach has been used for development, but the evolution team prefer to use agile methods. The evolution team may have to start from scratch developing automated tests and the code in the system may not have been refactored and simplified as is expected in agile development. Advanced Software Engineering 2024-2025  Legacy systems Advanced Software Engineering 2024-2025 Legacy systems Legacy systems are older systems that rely on languages and technology that are no longer used for new systems development. Legacy software may be dependent on older hardware, such as mainframe computers and may have associated legacy processes and procedures. Legacy systems are not just software systems but are broader socio- technical systems that include hardware, software, libraries and other supporting software and business processes. Advanced Software Engineering 2024-2025 The elements of a legacy system Advanced Software Engineering 2024-2025 Legacy system components 1. System hardware Legacy systems may have been written for hardware that is no longer available. 2. Support software The legacy system may rely on a range of support software, which may be obsolete or unsupported. 3. Application software The application system that provides the business services is usually made up of a number of application programs. 4. Application data These are data that are processed by the application system. They may be inconsistent, duplicated or held in different databases. Advanced Software Engineering 2024-2025 Legacy system components 5. Business processes These are processes that are used in the business to achieve some business objective. 6. Business processes may be designed around a legacy system and constrained by the functionality that it provides. 7. Business policies and rules These are definitions of how the business should be carried out and constraints on the business. Use of the legacy application system may be embedded in these policies and rules. Advanced Software Engineering 2024-2025 Legacy system layers Advanced Software Engineering 2024-2025 Legacy system replacement Legacy system replacement is risky and expensive so businesses continue to use these systems System replacement is risky for a number of reasons Lack of complete system specification Tight integration of system and business processes Undocumented business rules embedded in the legacy system New software development may be late and/or over budget Advanced Software Engineering 2024-2025 Legacy system change Legacy systems are expensive to change for a number of reasons: No consistent programming style Use of obsolete programming languages with few people available with these language skills Inadequate system documentation System structure degradation Program optimizations may make them hard to understand Data errors, duplication and inconsistency Advanced Software Engineering 2024-2025 Legacy system management Organizations that rely on legacy systems must choose a strategy for evolving these systems Scrap the system completely and modify business processes so that it is no longer required; Continue maintaining the system; Transform the system by re-engineering to improve its maintainability; Replace the system with a new system. The strategy chosen should depend on the system quality and its business value. Advanced Software Engineering 2024-2025 An example of a legacy system assessment Advanced Software Engineering 2024-2025 Legacy system categories Low quality, low business value These systems should be scrapped. Low-quality, high-business value These make an important business contribution but are expensive to maintain. Should be re-engineered or replaced if a suitable system is available. High-quality, low-business value Replace with COTS, scrap completely or maintain. High-quality, high business value Continue in operation using normal system maintenance. Advanced Software Engineering 2024-2025 Business value assessment Assessment should take different viewpoints into account System end-users; Business customers; Line managers; IT managers; Senior managers. Interview different stakeholders and collate results. Advanced Software Engineering 2024-2025 Issues in business value assessment 1. The use of the system If systems are only used occasionally or by a small number of people, they may have a low business value. 2. The business processes that are supported A system may have a low business value if it forces the use of inefficient business processes. 3. System dependability If a system is not dependable and the problems directly affect business customers, the system has a low business value. 4. The system outputs If the business depends on system outputs, then the system has a high business value. Advanced Software Engineering 2024-2025 System quality assessment Business process assessment How well does the business process support the current goals of the business? Environment assessment How effective is the system’s environment and how expensive is it to maintain? Application assessment What is the quality of the application software system? Advanced Software Engineering 2024-2025 Business process assessment Use a viewpoint-oriented approach and seek answers from system stakeholders Is there a defined process model and is it followed? Do different parts of the organisation use different processes for the same function? How has the process been adapted? What are the relationships with other business processes and are these necessary? Is the process effectively supported by the legacy application software? Example - a travel ordering system may have a low business value because of the widespread use of web-based ordering. Advanced Software Engineering 2024-2025 Factors used in environment assessment Factor Questions Supplier stability Is the supplier still in existence? Is the supplier financially stable and likely to continue in existence? If the supplier is no longer in business, does someone else maintain the systems? Failure rate Does the hardware have a high rate of reported failures? Does the support software crash and force system restarts? Age How old is the hardware and software? The older the hardware and support software, the more obsolete it will be. It may still function correctly but there could be significant economic and business benefits to moving to a more modern system. Performance Is the performance of the system adequate? Do performance problems have a significant effect on system users? Advanced Software Engineering 2024-2025 Factors used in environment assessment Factor Questions Support requirements What local support is required by the hardware and software? If there are high costs associated with this support, it may be worth considering system replacement. Maintenance costs What are the costs of hardware maintenance and support software licences? Older hardware may have higher maintenance costs than modern systems. Support software may have high annual licensing costs. Interoperability Are there problems interfacing the system to other systems? Can compilers, for example, be used with current versions of the operating system? Is hardware emulation required? Advanced Software Engineering 2024-2025  Factors used in application assessment Factor Questions Understandability How difficult is it to understand the source code of the current system? How complex are the control structures that are used? Do variables have meaningful names that reflect their function? Documentation What system documentation is available? Is the documentation complete, consistent, and current? Data Is there an explicit data model for the system? To what extent is data duplicated across files? Is the data used by the system up to date and consistent? Performance Is the performance of the application adequate? Do performance problems have a significant effect on system users? Advanced Software Engineering 2024-2025 Factors used in application assessment Factor Questions Programming language Are modern compilers available for the programming language used to develop the system? Is the programming language still used for new system development? Configuration Are all versions of all parts of the system managed by a management configuration management system? Is there an explicit description of the versions of components that are used in the current system? Test data Does test data for the system exist? Is there a record of regression tests carried out when new features have been added to the system? Personnel skills Are there people available who have the skills to maintain the application? Are there people available who have experience with the system? Advanced Software Engineering 2024-2025 System measurement You may collect quantitative data to make an assessment of the quality of the application system The number of system change requests; The higher this accumulated value, the lower the quality of the system. The number of different user interfaces used by the system; The more interfaces, the more likely it is that there will be inconsistencies and redundancies in these interfaces. The volume of data used by the system. As the volume of data (number of files, size of database, etc.) processed by the system increases, so too do the inconsistencies and errors in that data. Cleaning up old data is a very expensive and time-consuming process Advanced Software Engineering 2024-2025  Software maintenance Advanced Software Engineering 2024-2025 Software maintenance Modifying a program after it has been put into use. The term is mostly used for changing custom software. Generic software products are said to evolve to create new versions. Maintenance does not normally involve major changes to the system’s architecture. Changes are implemented by modifying existing components and adding new components to the system. Advanced Software Engineering 2024-2025 Types of maintenance Fault repairs Changing a system to fix bugs/vulnerabilities and correct deficiencies in the way meets its requirements. Environmental adaptation Maintenance to adapt software to a different operating environment Changing a system so that it operates in a different environment (computer, OS, etc.) from its initial implementation. Functionality addition and modification Modifying the system to satisfy new requirements. Advanced Software Engineering 2024-2025  Why modifications are required Market Conditions - Policies, which changes over the time, such as taxation and newly introduced constraints like, how to maintain bookkeeping, may trigger need for modification. Client Requirements - Over the time, customer may ask for new features or functions in the software. Host Modifications - If any of the hardware and/or platform (such as operating system) of the target host changes, software changes are needed to keep adaptability. Organization Changes - If there is any business level change at client end, such as reduction of organization strength, acquiring another company, organization venturing into new business, need to modify in the original software may arise. Advanced Software Engineering 2024-2025 Types of maintenance Corrective Maintenance - This includes modifications and updations done in order to correct or fix problems, which are either discovered by user or concluded by user error reports. Adaptive Maintenance - This includes modifications and updations applied to keep the software product up-to date and tuned to the ever changing world of technology and business environment. Perfective Maintenance - This includes modifications and updates done in order to keep the software usable over long period of time. It includes new features, new user requirements for refining the software and improve its reliability and performance. Preventive Maintenance - This includes modifications and updations to prevent future problems of the software. It aims to attend problems, which are not significant at this moment but may cause serious issues in future. Advanced Software Engineering 2024-2025 Maintenance effort distribution Advanced Software Engineering 2024-2025 Maintenance costs Usually greater than development costs (2* to 100* depending on the application). Affected by both technical and non-technical factors. Increases as software is maintained. Maintenance corrupts the software structure so makes further maintenance more difficult. Ageing software can have high support costs (e.g. old languages, compilers etc.). Advanced Software Engineering 2024-2025 Maintenance costs It is usually more expensive to add new features to a system during maintenance than it is to add the same features during development A new team has to understand the programs being maintained Separating maintenance and development means there is no incentive for the development team to write maintainable software Program maintenance work is unpopular Maintenance staff are often inexperienced and have limited domain knowledge. As programs age, their structure degrades, and they become harder to change Advanced Software Engineering 2024-2025  Software maintenance cost factors: The main differences between development and maintenance, as well as the t hings that make maintenance more expensive, can be broken down into two s ubcategories: 1.Non-Technical factors 2.Technical factors Technical factors: Non-Technical factors: Technical factors include the following: The Non-Technical factors include: 1.module independence 1.Application Domain 2.Programming language 2.Staff stability 3.Programming style 3.Program lifetime 4.Program validation and testing 4.Dependence on External Environment 5.Documentation 5.Hardware stability 6.Configuration management techniques Advanced Software Engineering 2024-2025  Maintenance efforts may be separated into productive activities (for example analysis and evaluation, design and modification, coding). A module of maintenance activities is provided by the following expression: M = P + K(C - D) where, M: Total effort expanded on the maintenance. P: Productive effort. K: An empirical constant. C: A measure of complexity that can be attributed to a lack of good design and documentation. D: A measure of the degree of familiarity with the software. Advanced Software Engineering 2024-2025 Maintenance prediction Maintenance prediction is concerned with assessing which parts of the system may cause problems and have high maintenance costs Change acceptance depends on the maintainability of the components affected by the change; Implementing changes degrades the system and reduces its maintainability; Maintenance costs depend on the number of changes and costs of change depend on maintainability. Advanced Software Engineering 2024-2025 Maintenance prediction Advanced Software Engineering 2024-2025 Change prediction Predicting the number of changes requires and understanding of the relationships between a system and its environment. Tightly coupled systems require changes whenever the environment is changed. Factors influencing this relationship are Number and complexity of system interfaces; Number of inherently volatile system requirements; The business processes where the system is used. Advanced Software Engineering 2024-2025 Complexity metrics Predictions of maintainability can be made by assessing the complexity of system components. Studies have shown that most maintenance effort is spent on a relatively small number of system components. Complexity depends on Complexity of control structures; Complexity of data structures; Object, method (procedure) and module size. Advanced Software Engineering 2024-2025 Process metrics Process metrics may be used to assess maintainability Number of requests for corrective maintenance; Average time required for impact analysis; 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. Advanced Software Engineering 2024-2025 Software reengineering Restructuring or rewriting part or all of a legacy system without changing its functionality. Applicable where some but not all sub-systems of a larger system require frequent maintenance. Reengineering involves adding effort to make them easier to maintain. The system may be re-structured and re-documented. Advanced Software Engineering 2024-2025 Advantages of reengineering Reduced risk There is a high risk in new software development. There may be development problems, staffing problems and specification problems. Reduced cost The cost of re-engineering is often significantly less than the costs of developing new software. Advanced Software Engineering 2024-2025 The reengineering process Advanced Software Engineering 2024-2025 Reengineering process activities Source code translation Convert code to a new language. Reverse engineering Analyse the program to understand it; Program structure improvement Restructure automatically for understandability; Program modularisation Reorganise the program structure; Data reengineering Clean-up and restructure system data. Advanced Software Engineering 2024-2025 Reengineering approaches Advanced Software Engineering 2024-2025 Reengineering cost factors The quality of the software to be reengineered. The tool support available for reengineering. The extent of the data conversion which is required. The availability of expert staff for reengineering. This can be a problem with old systems based on technology that is no longer widely used. Advanced Software Engineering 2024-2025 Refactoring Refactoring is the process of making improvements to a program to slow down degradation through change. You can think of refactoring as ‘preventative maintenance’ that reduces the problems of future change. Refactoring involves modifying a program to improve its structure, reduce its complexity or make it easier to understand. When you refactor a program, you should not add functionality but rather concentrate on program improvement. Advanced Software Engineering 2024-2025 Refactoring and reengineering Re-engineering takes place after a system has been maintained for some time and maintenance costs are increasing. You use automated tools to process and re-engineer a legacy system to create a new system that is more maintainable. Refactoring is a continuous process of improvement throughout the development and evolution process. It is intended to avoid the structure and code degradation that increases the costs and difficulties of maintaining a system. Advanced Software Engineering 2024-2025 ‘Bad smells’ in program code Duplicate code The same or very similar code may be included at different places in a program. This can be removed and implemented as a single method or function that is called as required. Long methods If a method is too long, it should be redesigned as a number of shorter methods. Switch (case) statements These often involve duplication, where the switch depends on the type of a value. The switch statements may be scattered around a program. In object-oriented languages, you can often use polymorphism to achieve the same thing. Advanced Software Engineering 2024-2025 ‘Bad smells’ in program code Data clumping Data clumps occur when the same group of data items (fields in classes, parameters in methods) re-occur in several places in a program. These can often be replaced with an object that encapsulates all of the data. Speculative generality This occurs when developers include generality in a program in case it is required in the future. This can often simply be removed. Advanced Software Engineering 2024-2025  Key points Software development and evolution can be thought of as an integrated, iterative process that can be represented using a spiral model. For custom systems, the costs of software maintenance usually exceed the software development costs. The process of software evolution is driven by requests for changes and includes change impact analysis, release planning and change implementation. Legacy systems are older software systems, developed using obsolete software and hardware technologies, that remain useful for a business. Advanced Software Engineering 2024-2025 Key points It is often cheaper and less risky to maintain a legacy system than to develop a replacement system using modern technology. The business value of a legacy system and the quality of the application should be assessed to help decide if a system should be replaced, transformed or maintained. There are 3 types of software maintenance, namely bug fixing, modifying software to work in a new environment, and implementing new or changed requirements. Advanced Software Engineering 2024-2025  Key points Software re-engineering is concerned with re-structuring and re- documenting software to make it easier to understand and change. Refactoring, making program changes that preserve functionality, is a form of preventative maintenance. Advanced Software Engineering 2024-2025