Chapter 9 - Software Evolution PDF

Chapter 9 – Software Evolution Evolution processes Legacy systems 30/10/2014 Chapter 9 Software Evolution 1 Software change Software change is inevitable New requirements emerge when the software is used; The business environment changes;...

Chapter 9 – Software Evolution Evolution processes Legacy systems 30/10/2014 Chapter 9 Software Evolution 1 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. 30/10/2014 Chapter 9 Software Evolution 2 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. 30/10/2014 Chapter 9 Software Evolution 3 A spiral model of development and evolution 30/10/2014 Chapter 9 Software Evolution 4 Evolution and servicing 30/10/2014 Chapter 9 Software Evolution 5 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. 30/10/2014 Chapter 9 Software Evolution 6 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. Change identification and evolution continues throughout the system lifetime. 30/10/2014 Chapter 9 Software Evolution 7 Change identification and evolution processes 30/10/2014 Chapter 9 Software Evolution 8 The software evolution process 30/10/2014 Chapter 9 Software Evolution 9 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). 30/10/2014 Chapter 9 Software Evolution 10 The emergency repair process 30/10/2014 Chapter 9 Software Evolution 11 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. 30/10/2014 Chapter 9 Software Evolution 12 The elements of a legacy system 30/10/2014 Chapter 9 Software Evolution 13 Legacy system components System hardware Legacy systems may have been written for hardware that is no longer available. Support software The legacy system may rely on a range of support software, which may be obsolete or unsupported. Application software The application system that provides the business services is usually made up of a number of application programs. Application data These are data that are processed by the application system. They may be inconsistent, duplicated or held in different databases. 30/10/2014 Chapter 9 Software Evolution 14 Legacy system components Business processes These are processes that are used in the business to achieve some business objective. 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. 30/10/2014 Chapter 9 Software Evolution 15 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 30/10/2014 Chapter 9 Software Evolution 16 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 Data errors, duplication and inconsistency 30/10/2014 Chapter 9 Software Evolution 17 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. 30/10/2014 Chapter 9 Software Evolution 18 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 30/10/2014 Chapter 9 Software Evolution 19 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. 30/10/2014 Chapter 9 Software Evolution 20