CH09-Software Evolution PDF

CPT 441 CSE241/CMM341 Software Quality Foundations Assurance of Software & Testing Engineering Photo credit: Dreamstime.com Topic: Software Evolution Topic 9. Software Evolution 1. Evolu...

CPT 441 CSE241/CMM341 Software Quality Foundations Assurance of Software & Testing Engineering Photo credit: Dreamstime.com Topic: Software Evolution Topic 9. Software Evolution 1. Evolution processes 2. Legacy systems 3. Software maintenance 2 Software Change Software change is inevitable. Why do we need to change? New requirements The business Errors must be emerge when the environment repaired; software is used; changes; New computers The performance and equipment is or reliability of the added to the system may have system; to be improved. A key problem for all organizations is implementing and managing change to their existing software systems. 3  Software systems is one of the critical business assets. Importance of evolution To maintain the value of these assets to the business, they must be changed and updated. 4 A spiral model of development and evolution 5 Evolution and servicing software system is software remains software in operational use useful but the only may still be and is evolving as changes made to used but no new requirements keep it operational. further. are proposed and No new implemented in functionality is the system. added. 6 1. Evolution processes 7 Evolution processes – areas of consideration Software evolution processes depend on The type of software being maintained; The development processes used; The skills and experience of the people involved. 8  Change identification and evolution processes  10 The software evolution process Change Implementation Iteration of the development process where the revisions to the system are designed, implemented and tested. The first stage of change implementation involve program understanding Important if the original system developers are not responsible for the change implementation. understand how the program is structured, how it delivers functionality and how the proposed change might affect the program. 11 Urgent Change Requests Urgent changes may have to be implemented without going through all stages of the software engineering process. When? 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). 12 The Emergency Repair Process 13  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 Agile releases. methods and Automated regression testing is particularly evolution valuable when changes are made to a system. Changes may be expressed as additional user stories. 14 Program Evolution Dynamics – Lehman’s Laws 15  Part 2: Legacy systems 16 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. 17 18 19 20  BASIC Programming for MS DOS 21  Database for MS DOS 22 The elements of a legacy system The application system that Definitions of how the Legacy system may rely business should be provides the business services on a range of support carried out and that made up of a number of software, which may be constraints on the application programs obsolete or unsupported. business Legacy systems may Data that are processed by Processes that are have been written for the application system, may used in the business to hardware that is no be inconsistent, duplicated achieve some business longer available or held in different objective. databases. 23 Legacy system replacement System replacement is risky and expensive 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 24 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 25  Legacy system management Organisations 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. 26  Figure 9.13 An example of a legacy system assessment Should be re- engineered or Continue in replaced if a operation using suitable system is normal system available maintenance. Replace with COTS, scrap completely or systems maintain should be scrapped 27  Business Assessment should take different viewpoints into account value System end-users; assessment Business customers; Line managers; IT managers; Senior managers. Interview different stakeholders and collate results. 28 Issues in Business Value Assessment If systems are only used occasionally or by a small The use of the number of people, they may have a low business system value. The business A system may have a low business value if it forces processes that are the use of inefficient business processes. supported If a system is not dependable and the problems System directly affect business customers, the system has a dependability low business value. The system If the business depends on system outputs, then the outputs system has a high business value. 29  Business process assessment How well does the business process support the current goals of the business? System quality Environment assessment 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? 30 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. 31  Factors used in environment assessment (1/3) 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? 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. 32  Factors used in application assessment (2/3) 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? 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? 33  Factors used in application assessment (3/3) Factors used in application assessment (2/2) Factor Questions Configuration Are all versions of all parts of the system managed by a configuration management 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? 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? 34  Cinema Time! ▪ Legacy System Modernization: Why Businesses Should Upgrade Their Legacy Systems? ▪ https://www.youtube.com/watch?v=S4M1AhMN_l4 35  Part 3: Software maintenance 36 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. 37 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. 38 Maintenance effort distribution 39  Maintenance costs (1/2) 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.). 40  Maintenance costs (2/2) 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  Example Source: http://www.iceaaonline.com/ready/wp- content/uploads/2015/06/SW08-Presentation- 42 Jones-Software-Maintenance.pdf  Example Source: http://www.iceaaonline.com/ready/wp-content/uploads/2015/06/SW08- Presentation-Jones-Software-Maintenance.pdf 43 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. 44 Maintenance prediction 45  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. Change prediction 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. 46 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. 47 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. 48 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. 49 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. 50 The Reengineering Process 51 The reengineering process 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. 52 Reengineering approaches 53  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. 54  Refactoring Refactoring is the process of making improvements to a program to slow down degradation through change. A ‘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. Did not add functionality but rather concentrate on program improvement 55  Refactoring and reengineering Re-engineering takes place after a system has been maintained for some time and maintenance costs are increasing. use automated tools to process and re-engineer a legacy system to create a new system that is more maintainable. Refactoring a continuous process of improvement throughout the development and evolution process. Purpose to avoid the structure and code degradation that increases the costs and difficulties of maintaining a system. 56 ‘Bad smells’ in program code Duplicate The same or very similar code may be included at different code 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) These often involve duplication, where the switch depends statements 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. 57 ‘Bad smells’ in program code Data Data clumps occur when the same group of data clumping 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. 58  Cinema Time Again! ▪ Did the World Almost End in 2000 Because of Y2K? ▪ https://www.youtube.com/watch?v=l0Lfp_ghlGM 59 Key points (1/3) ▪ 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. 60 Key points (2/3) ▪ 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. 61 Key points (3/3) ▪ 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. 62