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Software maintenance in software engineering is the modification of a software product after delivery to correct faults, to improve performance or other attributes.
Software engineering is the application of engineering to the development of software in a systematic method.
A common perception of maintenance is that it merely involves fixing defects. However, one study indicated that over 80% of maintenance effort is used for non-corrective actions. [ citation needed ] More recent studies put the bug-fixing proportion closer to 21%.This perception is perpetuated by users submitting problem reports that in reality are functionality enhancements to the system.
A software bug is an error, flaw, failure or fault in a computer program or system that causes it to produce an incorrect or unexpected result, or to behave in unintended ways. The process of finding and fixing bugs is termed "debugging" and often uses formal techniques or tools to pinpoint bugs, and since the 1950s, some computer systems have been designed to also deter, detect or auto-correct various computer bugs during operations.
Software maintenance and evolution of systems was first addressed by Meir M. Lehman in 1969. Over a period of twenty years, his research led to the formulation of Lehman's Laws (Lehman 1997). Key findings of his research conclude that maintenance is really evolutionary development and that maintenance decisions are aided by understanding what happens to systems (and software) over time. Lehman demonstrated that systems continue to evolve over time. As they evolve, they grow more complex unless some action such as code refactoring is taken to reduce the complexity.
Software evolution is the term used in software engineering to refer to the process of developing software initially, then repeatedly updating it for various reasons.
Code refactoring is the process of restructuring existing computer code—changing the factoring—without changing its external behavior. Refactoring is intended to improve nonfunctional attributes of the software. Advantages include improved code readability and reduced complexity; these can improve source-code maintainability and create a more expressive internal architecture or object model to improve extensibility.
In the late 1970s, a famous and widely cited survey study by Lientz and Swanson, exposed the very high fraction of life-cycle costs that were being expended on maintenance. They categorized maintenance activities into four classes:
Whole-life cost, or Life-cycle cost (LCC), refers to the total cost of ownership over the life of an asset. Also commonly referred to as "cradle to grave" or "womb to tomb" costs. Costs considered include the financial cost which is relatively simple to calculate and also the environmental and social costs which are more difficult to quantify and assign numerical values. Typical areas of expenditure which are included in calculating the whole-life cost include planning, design, construction and acquisition, operations, maintenance, renewal and rehabilitation, depreciation and cost of finance and replacement or disposal.
An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs.
The survey showed that around 75% of the maintenance effort was on the first two types, and error correction consumed about 21%. Many subsequent studies suggest a similar problem magnitude. Studies show that contribution of end users is crucial during the new requirement data gathering and analysis. This is the main cause of any problem during software evolution and maintenance. Software maintenance is important because it consumes a large part of the overall lifecycle costs and also the inability to change software quickly and reliably means that business opportunities are lost.
The key software maintenance issues are both managerial and technical. Key management issues are: alignment with customer priorities, staffing, which organization does maintenance, estimating costs. Key technical issues are: limited understanding, impact analysis, testing, maintainability measurement.
Software maintenance is a very broad activity that includes error correction, enhancements of capabilities, deletion of obsolete capabilities, and optimization. Because change is inevitable, mechanisms must be developed for evaluation, controlling and making modifications.
So any work done to change the software after it is in operation is considered to be maintenance work. The purpose is to preserve the value of software over the time. The value can be enhanced by expanding the customer base, meeting additional requirements, becoming easier to use, more efficient and employing newer technology. Maintenance may span for 20 years,[ citation needed ] whereas development may be 1–2 years.[ citation needed ]
An integral part of software is the maintenance one, which requires an accurate maintenance plan to be prepared during the software development. It should specify how users will request modifications or report problems. The budget should include resource and cost estimates. A new decision should be addressed for the developing of every new system feature and its quality objectives. The software maintenance, which can last for 5–6 years (or even decades) after the development process, calls for an effective plan which can address the scope of software maintenance, the tailoring of the post delivery/deployment process, the designation of who will provide maintenance, and an estimate of the life-cycle costs. The selection of proper enforcement of standards is the challenging task right from early stage of software engineering which has not got definite importance by the concerned stakeholders.
This section describes the six software maintenance processes as:
There are a number of processes, activities and practices that are unique to maintainers, for example:
E.B. Swanson initially identified three categories of maintenance: corrective, adaptive, and perfective.The IEEE 1219 standard was superseded in June 2010 by P14764. These have since been updated and ISO/IEC 14764 presents:
There is also a notion of pre-delivery/pre-release maintenance which is all the good things you do to lower the total cost of ownership of the software. Things like compliance with coding standards that includes software maintainability goals. The management of coupling and cohesion of the software. The attainment of software supportability goals (SAE JA1004, JA1005 and JA1006 for example). Note also that some academic institutions[ who? ] are carrying out research to quantify the cost to ongoing software maintenance due to the lack of resources such as design documents and system/software comprehension training and resources (multiply costs by approx. 1.5-2.0 where there is no design data available).
Impact of key adjustment factors on maintenance (sorted in order of maximum positive impact)
|Maintenance Factors||Plus Range|
|High staff experience||34%|
|Table-driven variables and data||33%|
|Low complexity of base code||32%|
|Y2K and special search engines||30%|
|Code restructuring tools||29%|
|High level programming languages||25%|
|Reverse engineering tools||23%|
|Complexity analysis tools||20%|
|Defect tracking tools||20%|
|Y2K “mass update” specialists||20%|
|Automated change control tools||18%|
|Formal base code inspections||15%|
|Regression test libraries||15%|
|Excellent response time||12%|
|Annual training of > 10 days||12%|
|High management experience||12%|
|HELP desk automation||12%|
|No error prone modules||10%|
|On-line defect reporting||10%|
|Excellent ease of use||7%|
|User satisfaction measurements||5%|
|High team morale||5%|
Not only are error-prone modules troublesome, but many other factors can degrade performance too. For example, very complex spaghetti code is quite difficult to maintain safely. A very common situation which often degrades performance is lack of suitable maintenance tools, such as defect tracking software, change management software, and test library software. Below describe some of the factors and the range of impact on software maintenance.
Impact of key adjustment factors on maintenance (sorted in order of maximum negative impact)
|Maintenance Factors||Minus Range|
|Error prone modules||-50%|
|Embedded variables and data||-45%|
|High code complexity||-30%|
|No Y2K of special search engines||-28%|
|Manual change control methods||-27%|
|Low level programming languages||-25%|
|No defect tracking tools||-24%|
|No Y2K “mass update” specialists||-22%|
|Poor ease of use||-18%|
|No quality measurements||-18%|
|No maintenance specialists||-18%|
|Poor response time||-16%|
|No code inspections||-15%|
|No regression test libraries||-15%|
|No help desk automation||-15%|
|No on-line defect reporting||-12%|
|No code restructuring tools||-10%|
|No annual training||-10%|
|No reengineering tools||-10%|
|No reverse-engineering tools||-10%|
|No complexity analysis tools||-10%|
|No productivity measurements||-7%|
|Poor team morale||-6%|
|No user satisfaction measurements||-4%|
|No unpaid overtime||0%|
The Software Engineering Body of Knowledge (SWEBOK) is an international standard ISO/IEC TR 19759:2005 specifying a guide to the generally accepted Software Engineering Body of Knowledge.
Configuration management (CM) is a systems engineering process for establishing and maintaining consistency of a product's performance, functional, and physical attributes with its requirements, design, and operational information throughout its life. The CM process is widely used by military engineering organizations to manage changes throughout the system lifecycle of complex systems, such as weapon systems, military vehicles, and information systems. Outside the military, the CM process is also used with IT service management as defined by ITIL, and with other domain models in the civil engineering and other industrial engineering segments such as roads, bridges, canals, dams, and buildings.
Software architecture refers to the high level structures of a software system and the discipline of creating such structures and systems. Each structure comprises software elements, relations among them, and properties of both elements and relations. The architecture of a software system is a metaphor, analogous to the architecture of a building. It functions as a blueprint for the system and the developing project, laying out the tasks necessary to be executed by the design teams.
Software development is the process of conceiving, specifying, designing, programming, documenting, testing, and bug fixing involved in creating and maintaining applications, frameworks, or other software components. Software development is a process of writing and maintaining the source code, but in a broader sense, it includes all that is involved between the conception of the desired software through to the final manifestation of the software, sometimes in a planned and structured process. Therefore, software development may include research, new development, prototyping, modification, reuse, re-engineering, maintenance, or any other activities that result in software products.
The following outline is provided as an overview of and topical guide to software engineering:
ISO/IEC/IEEE 12207Systems and software engineering – Software life cycle processes is an international standard for software lifecycle processes. First introduced in 1995, it aims to be a primary standard that defines all the processes required for developing and maintaining software systems, including the outcomes and/or activities of each process.
Requirements engineering (RE) refers to the process of defining, documenting and maintaining requirements in the engineering design process. It is a common role in systems engineering and software engineering.
A software requirements specification (SRS) is a description of a software system to be developed. It is modeled after business requirements specification(CONOPS), also known as a stakeholder requirements specification (StRS). The software requirements specification lays out functional and non-functional requirements, and it may include a set of use cases that describe user interactions that the software must provide.
In the context of software engineering, software quality refers to two related but distinct notions:
Integrated logistic support (ILS) is an integrated and iterative process for developing materiel and a support strategy that optimizes functional support, leverages existing resources, and guides the system engineering process to quantify and lower life cycle cost and decrease the logistics footprint, making the system easier to support. Although originally developed for military purposes, it is also widely used in commercial product support or customer service organisations.
The change management process in systems engineering is the process of requesting, determining attainability, planning, implementing, and evaluating of changes to a system. Its main goals are to support the processing and traceability of changes to an interconnected set of factors.
IEEE 1471 is a superseded IEEE Standard for describing the architecture of a "software-intensive system", also known as software architecture.
International standards in the ISO/IEC 19770 family of standards for IT asset management (ITAM) address both the processes and technology for managing software assets and related IT assets. Broadly speaking, the standard family belongs to the set of Software Asset Management standards and is integrated with other Management System Standards.
Quality engineering is the discipline of engineering concerned with the principles and practice of product and service quality assurance and control. In the software development, it is the management, development, operation and maintenance of IT systems and enterprise architectures with a high quality standard.
ISO/IEC/IEEE 42010Systems and software engineering — Architecture description is an international standard for architecture descriptions of systems and software.
ISO/IEC 29110: Systems and Software Life Cycle Profiles and Guidelines for Very Small Entities (VSEs) International Standards (IS) and Technical Reports (TR) are targeted at Very Small Entities (VSEs). A Very Small Entity (VSE) is an enterprise, an organization, a department or a project having up to 25 people. The ISO/IEC 29110 is a series of international standards and guides entitled "Systems and Software Engineering — Lifecycle Profiles for Very Small Entities (VSEs)". The standards and technical reports were developed by working group 24 (WG24) of sub-committee 7 (SC7) of Joint Technical Committee 1 (JTC1) of the International Organization for Standardization and the International Electrotechnical Commission.
ITIL, formerly an acronym for Information Technology Infrastructure Library, is a set of detailed practices for IT service management (ITSM) that focuses on aligning IT services with the needs of business.