Software Processes

Extract

[...] Should start with poorly understood requirements Develop “quick and dirty” system quickly; Expose to user comment; Refine; Until adequate system developed. Particularly suitable where: detailed requirements not possible; powerful development tools (e.g. GUI) available Evolutionary development Problems Lack of process visibility Systems are often poorly structured Special skills (e.g. in languages for rapid prototyping) may be required Applicability For small or medium-size interactive systems For parts of large systems (e.g. the user interface) For short-lifetime systems Formal systems development Based on the transformation of a mathematical specification through different representations to an executable program Transformations are ‘correctness-preserving' so it is straightforward to show that the program conforms to its specification Formal systems development Problems Need for specialised skills and training to apply the technique Difficult to formally specify some aspects of the system such as the user interface Applicability Critical systems especially those where a safety or security case must be made before the system is put into operation Reuse-oriented development Based on systematic reuse where systems are integrated from existing components or COTS (Commercial-off-the-shelf) systems Process stages Component analysis Requirements modification System design with reuse Development and integration Process iteration Modern development processes take iteration as fundamental, and try to provide ways of managing, rather than ignoring, the risk System requirements ALWAYS evolve in the course of a project so process iteration where earlier stages are reworked is always part of the process for large systems Iteration can be applied to any of the generic process models Two (related) approaches Incremental development Spiral development Incremental development Rather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality User requirements are prioritised and the highest priority requirements are included in early increments Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve Incremental development advantages Customer value can be delivered with each increment so system functionality is available earlier Early increments act as a prototype to help elicit requirements for later increments Lower risk of overall project failure The highest priority system services tend to receive the most testing Extreme programming New approach to development based on the development and delivery of very small increments of functionality Relies on constant code improvement, user involvement in the development team and pairwise programming Spiral development Process is represented as a spiral rather than as a sequence of activities with backtracking Each loop in the spiral represents a phase in the process. [...]

[...] to develop a software system Specification Design Validation Evolution A software process model is an abstract representation of a process It presents a description of a process from some particular perspective Generic Software Process Models The waterfall model Separate and distinct phases of specification and development Evolutionary development Specification and development are interleaved Formal systems development A mathematical system model is formally transformed to an implementation Reuse-based development The system is assembled from existing components Waterfall model phases Requirements analysis and definition System and software design Implementation and unit testing Integration and system testing Operation and maintenance The drawback of the waterfall model is the difficulty of accommodating change after the process is underway Waterfall model problems Inflexible partitioning of the project into distinct stages This makes it difficult to respond to changing customer requirements Therefore, this model is only appropriate when the requirements are well understood Why Not a Waterfall No fabrication step Program code is another design level Hence, no step software can always be changed ! [...]

[...] They are represented in a software process model General activities are specification, design and implementation, validation and evolution Generic process models describe the organisation of software processes Iterative process models describe the software process as a cycle of activities Key points Requirements engineering is the process of developing a software specification Design and implementation processes transform the specification to an executable program Validation involves checking that the system meets to its specification and user needs Evolution is concerned with modifying the system after it is in use CASE technology supports software process activities BIBLIOGRAPHY SOFTWARE ENGINEERING BY RAJEEV MALL Default Design Software Processes Software Processes Coherent sets of activities for Specifying, Designing, Implementing and Testing software systems The Software Process A structured set of activities required to develop a software system Specification Design Validation Evolution A software process model is an abstract representation of a process It presents a description of a process from some particular perspective Generic Software Process Models The waterfall model Separate and distinct phases of specification and development Evolutionary development Specification and development are interleaved Formal systems development A mathematical system model is formally transformed to an implementation Reuse-based development The system is assembled from existing components Waterfall model phases Requirements analysis and definition System and software design Implementation and unit testing Integration and system testing Operation and maintenance The drawback of the waterfall model is the difficulty of accommodating change after the process is underway Waterfall model problems Inflexible partitioning of the project into distinct stages This makes it difficult to respond to changing customer requirements Therefore, this model is only appropriate when the requirements are well understood Why Not a Waterfall No fabrication step Program code is another design level Hence, no step software can always be changed ! [...]

[...] No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required Risks are explicitly assessed and resolved throughout the process Spiral model sectors Objective setting Specific objectives for the phase are identified Risk assessment and reduction Risks are assessed and activities put in place to reduce the key risks Development and validation A development model for the system is chosen which can be any of the generic models Planning The project is reviewed and the next phase of the spiral is planned Software specification The process of establishing what services are required and the constraints on the system's operation and development Requirements engineering process Feasibility study Requirements elicitation and analysis Requirements specification Requirements validation Software design and implementation The process of converting the system specification into an executable system Software design Design a software structure that realises the specification Implementation Translate this structure into an executable program The activities of design and implementation are closely related and may be inter-leaved Design process activities Architectural design Abstract specification Interface design Component design Data structure design Algorithm design Design methods Systematic approaches to developing a software design The design is usually documented as a set of graphical models Possible models Data-flow model Entity-relation-attribute model Structural model Object models Programming and debugging Translating a design into a program and removing errors from that program Programming is a personal activity - there is no generic programming process Programmers carry out some program testing to discover faults in the program and remove these faults in the debugging process Software validation Verification and validation is intended to show that a system conforms to its specification and meets the requirements of the system customer Involves checking and review processes and system testing System testing involves executing the system with test cases that are derived from the specification of the real data to be processed by the system Testing stages Unit testing Individual components are tested Module testing Related collections of dependent components are tested Sub-system testing Modules are integrated into sub-systems and tested. [...]

[...] As requirements change through changing business circumstances, the software that supports the business must also evolve and change Although there has been a demarcation between development and evolution (maintenance) this is increasingly irrelevant as fewer and fewer systems are completely new Automated process support (CASE) Computer-aided software engineering (CASE) is software to support software development and evolution processes Activity automation Graphical editors for system model development Data dictionary to manage design entities Graphical UI builder for user interface construction Debuggers to support program fault finding Automated translators to generate new versions of a program Case technology Case technology has led to significant improvements in the software process though not the order of magnitude improvements that were once predicted Software engineering requires creative thought - this is not readily automatable Software engineering is a team activity and, for large projects, much time is spent in team interactions. [...]