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CT-365 Software Engineering Course Instructor: Ms. Nudrat Naved Lecturer, Department of Computer Science and IT Software Engineering Software engineering is an engineering discipline that is concerned with all aspects of software production from the ear...

CT-365 Software Engineering Course Instructor: Ms. Nudrat Naved Lecturer, Department of Computer Science and IT Software Engineering Software engineering is an engineering discipline that is concerned with all aspects of software production from the early stages of system specification through to maintaining the system after it has gone into use. Engineering discipline Using appropriate theories and methods to solve problems bearing in mind organizational and financial constraints. All aspects of software production Not just technical process of development. Also project management and the development of tools, methods etc. to support software production. Importance of Software Engineering More and more, individuals and society rely on advanced software systems. We need to be able to produce reliable and trustworthy systems economically and quickly. It is usually cheaper, in the long run, to use software engineering methods and techniques for software systems rather than just write the programs as if it was a personal programming project. For most types of system, the majority of costs are the costs of changing the software after it has gone into use. Essential Attributes of Good Software Product characteristic Description Maintainability Software should be written in such a way so that it can evolve to meet the changing needs of customers. This is a critical attribute because software change is an inevitable requirement of a changing business environment. Dependability and Software dependability includes a range of characteristics security including reliability, security and safety. Dependable software should not cause physical or economic damage in the event of system failure. Malicious users should not be able to access or damage the system. Efficiency Software should not make wasteful use of system resources such as memory and processor cycles. Efficiency therefore includes responsiveness, processing time, memory utilisation, etc. Acceptability Software must be acceptable to the type of users for which it is designed. This means that it must be understandable, usable and compatible with other systems that they use. Software Engineering Fundamentals Some fundamental principles apply to all types of software system, irrespective of the development techniques used: Systems should be developed using a managed and understood development process. Of course, different processes are used for different types of software. Dependability and performance are important for all types of system. Understanding and managing the software specification and requirements (what the software should do) are important. Where appropriate, you should reuse software that has already been developed rather than write new software. General Issues that Affect Software Heterogeneity The need to design and develop applications differently for different hardware architectures Increasingly, systems are required to operate as distributed systems across networks that include different types of computer and mobile devices. Business and Social Change Business and society are changing incredibly quickly as emerging economies develop and new technologies become available. They need to be able to change their existing software and to rapidly develop new software. Security and Trust As software is intertwined with all aspects of our lives, it is essential that we can trust that software. Scale Software has to be developed across a very wide range of scales, from very small embedded systems in portable or wearable devices through to Internet-scale, cloud-based systems that serve a global community. FAQs about Software Engineering Question Answer What is software? Computer programs and associated documentation. Software products may be developed for a particular customer or may be developed for a general market. What are the attributes of good software? Good software should deliver the required functionality and performance to the user and should be maintainable, dependable and usable. What is software engineering? Software engineering is an engineering discipline that is concerned with all aspects of software production. What are the fundamental software Software specification, software development, software engineering activities? validation and software evolution. What is the difference between software Computer science focuses on theory and fundamentals; engineering and computer science? software engineering is concerned with the practicalities of developing and delivering useful software. What is the difference between software System engineering is concerned with all aspects of engineering and system engineering? computer-based systems development including hardware, software and process engineering. Software engineering is part of this more general process. FAQs about Software Engineering Question Answer What are the key challenges facing Coping with increasing diversity, demands for reduced software engineering? delivery times and developing trustworthy software. What are the costs of software Roughly 60% of software costs are development costs, engineering? 40% are testing costs. For custom software, evolution costs often exceed development costs. What are the best software engineering While all software projects have to be professionally techniques and methods? managed and developed, different techniques are appropriate for different types of system. For example, games should always be developed using a series of prototypes whereas safety critical control systems require a complete and analyzable specification to be developed. You can’t, therefore, say that one method is better than another. What differences has the web made to The web has led to the availability of software services software engineering? and the possibility of developing highly distributed service-based systems. Web-based systems development has led to important advances in programming languages and software reuse. Application Types Stand-Alone Applications These are application systems that run on a local computer, such as a PC. They include all necessary functionality and do not need to be connected to a network. Interactive Transaction-based Applications Applications that execute on a remote computer and are accessed by users from their own PCs or terminals. These include web applications such as e-commerce applications. Embedded Control Systems These are software control systems that control and manage hardware devices. Batch processing systems These are business systems that are designed to process data in large batches. They process large numbers of individual inputs to create corresponding outputs. Application Types Entertainment Systems These are systems that are primarily for personal use and which are intended to entertain the user. Systems for Modeling and Simulation These are systems that are developed by scientists and engineers to model physical processes or situations, which include many, separate, interacting objects. Data Collection Systems These are systems that collect data from their environment using a set of sensors and send that data to other systems for processing. Systems of Systems These are systems that are composed of a number of other software systems. Software Process Activities Software specification, where customers and engineers define the software that is to be produced and the constraints on its operation. Software development, where the software is designed and programmed. Software validation, where the software is checked to ensure that it is what the customer requires. Software evolution, where the software is modified to reflect changing customer and market requirements. Software Process Models A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective. Plan-driven processes are processes where all of the process activities are planned in advance and progress is measured against this plan. In agile processes, planning is incremental and it is easier to change the process to reflect changing customer requirements. In practice, most practical processes include elements of both plan-driven and agile approaches. There are no right or wrong software processes.  Waterfall Model Plan-driven model. Separate and distinct phases of specification and development. In principle, a phase has to be complete before moving onto the next phase. Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements. The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites.  Incremental Development The cost of accommodating changing customer requirements is reduced. It is easier to get customer feedback on the development work that has been done. More rapid delivery and deployment of useful software to the customer is possible. System structure tends to degrade as new increments are added. Unless time and money is spent on refactoring to improve the software, regular change tends to corrupt its structure. Spiral Model The Spiral Model is a combination of the waterfall model and the iterative model. It provides support for Risk Handling. The exact number of loops of the spiral is unknown and can vary from project to project. Each loop of the spiral is called a phase of the software development process. The Spiral model is called a Meta-Model because it subsumes all the other models. The Spiral Model is often used for complex and large software projects, as it provides flexibility in requirements and increases customer satisfaction. However, it is complex, expensive, and resource and time-consuming.  Prototyping A prototype is an initial version of a system used to demonstrate concepts and try out design options. A prototype can be used in: The requirements engineering process to help with requirements elicitation and validation; In design processes to explore options and Prototype Development develop a UI design; In the testing process to run back-to-back tests. Benefits include Improved system usability. A closer match to users’ real needs. Improved design quality. Improved maintainability. Throw-Away Prototype Agile Development Program specification, design and implementation are inter-leaved. The system is developed as a series of versions or increments with stakeholders involved in version specification and evaluation. Frequent delivery of new versions for evaluation. Extensive tool support for development. Minimal documentation – focus on working code. Methods: eXtreme Programming eXtreme programming (XP) takes an ‘extreme’ approach to iterative development. New versions may be built several times per day; Increments are delivered to customers every 2 weeks; All tests must be run for every build and the build is only accepted if tests run successfully. Extreme Programming Practices (a) Principle or practice Description Incremental planning Requirements are recorded on story cards and the stories to be included in a release are determined by the time available and their relative priority. The developers break these stories into development ‘Tasks’. See Figures 3.5 and 3.6. Small releases The minimal useful set of functionality that provides business value is developed first. Releases of the system are frequent and incrementally add functionality to the first release. Simple design Enough design is carried out to meet the current requirements and no more. Test-first development An automated unit test framework is used to write tests for a new piece of functionality before that functionality itself is implemented. Refactoring All developers are expected to refactor the code continuously as soon as possible code improvements are found. This keeps the code simple and maintainable. Extreme Programming Practices (b) Pair programming Developers work in pairs, checking each other’s work and providing the support to always do a good job. Collective ownership The pairs of developers work on all areas of the system, so that no islands of expertise develop and all the developers take responsibility for all of the code. Anyone can change anything. Continuous integration As soon as the work on a task is complete, it is integrated into the whole system. After any such integration, all the unit tests in the system must pass. Sustainable pace Large amounts of overtime are not considered acceptable as the net effect is often to reduce code quality and medium term productivity On-site customer A representative of the end-user of the system (the customer) should be available full time for the use of the XP team. In an extreme programming process, the customer is a member of the development team and is responsible for bringing system requirements to the team for implementation.  Methods: Scrum Scrum focuses on managing iterative development rather than specific agile practices. There are three phases in Scrum. The initial phase is an outline planning phase where you establish the general objectives for the project and design the software architecture. This is followed by a series of sprint cycles, where each cycle develops an increment of the system. The project closure phase wraps up the project, completes required documentation such as system help frames and user manuals and assesses the lessons learned from the project. Scrum Terminology (a) Scrum term Definition Development team A self-organizing group of software developers, which should be no more than 7 people. They are responsible for developing the software and other essential project documents. Potentially shippable The software increment that is delivered from a sprint. The idea is that this product increment should be ‘potentially shippable’ which means that it is in a finished state and no further work, such as testing, is needed to incorporate it into the final product. In practice, this is not always achievable. Product backlog This is a list of ‘to do’ items which the Scrum team must tackle. They may be feature definitions for the software, software requirements, user stories or descriptions of supplementary tasks that are needed, such as architecture definition or user documentation. Product owner An individual (or possibly a small group) whose job is to identify product features or requirements, prioritize these for development and continuously review the product backlog to ensure that the project continues to meet critical business needs. The Product Owner can be a customer but might also be a product manager in a software company or other stakeholder representative. Scrum Terminology (b) Scrum term Definition Scrum A daily meeting of the Scrum team that reviews progress and prioritizes work to be done that day. Ideally, this should be a short face-to-face meeting that includes the whole team. ScrumMaster The ScrumMaster is responsible for ensuring that the Scrum process is followed and guides the team in the effective use of Scrum. He or she is responsible for interfacing with the rest of the company and for ensuring that the Scrum team is not diverted by outside interference. The Scrum developers are adamant that the ScrumMaster should not be thought of as a project manager. Others, however, may not always find it easy to see the difference. Sprint A development iteration. Sprints are usually 2-4 weeks long. Velocity An estimate of how much product backlog effort that a team can cover in a single sprint. Understanding a team’s velocity helps them estimate what can be covered in a sprint and provides a basis for measuring improving performance. Agile Applicability Product development where a software company is developing a small or medium-sized product for sale. Virtually all software products and apps are now developed using an agile approach. Custom system development within an organization, where there is a clear commitment from the customer to become involved in the development process and where there are few external rules and regulations that affect the software. Criticisms: Unrealistic assumption where much of the actual development is off-shored, outsourced. “Programmers gone wild” environment, since it is not carefully managed. Concerns on suitability to deliver large mission-critical systems.