5 - software development processes.pdf

10/4/21 1 SOICT School of Information and Communication Technology 2 1 ...

10/4/21 1 SOICT School of Information and Communication Technology 2 1  10/4/21 IT3180 – Introduction to Software Engineering 5 – Software Development Processes 3 3 Sequence of Processes Lecture 3 introduced several process steps: Requirements User Interface Design System Design Program development (design and coding) Acceptance and release Every software project will include these basic steps, in some shape or form, but: The steps may be formal or informal The steps may be carried out in various sequences 4 4 2  10/4/21 A software development process or methodology is a systematic way of combining these steps to build a software system 5 5 Software Development Process In this lecture, we look at four categories of software development processes: Waterfall Complete each process step before beginning the next Iterative refinement Go quickly through all the steps to create a rough system, then repeat them to improve the system Spiral A variant of iterative refinement in which new and updated components are added to the developing system as they are completed Agile development: Small increments of software are developed in a sequence of sprints, each of which creates deployable code 6 6 3  10/4/21 Heavyweight and Lightweight Software Development Heavyweight Process Fully complete each step and have minimal changes and revisions later Each step is fully documented before beginning the next Example: waterfall or modified waterfall 7 7 Heavyweight and Lightweight Software Development Lightweight Process Expectation that changes will be made based on experience Minimal intermediate documentation Only the final system will be documented Example: Agile Software Development 8 8 4  10/4/21 Heavyweight vs. Lightweight Methodologies Heavyweight Lightweight Slower process Speedy process Release at the final stage Released as increments Client negotiation Client collaboration Following a plan Responding to change 9 9 History Software engineering became a discipline, dated from the early 1970s At that time: Most computer systems were conversions of systems that had previously been done manually (billing, airline reservation etc.) The requirements were well understood Many system followed the same architecture, Master File Update The system design was well understood Coding was tedious with none of the modern languages and tools It was important to have a good program design before coding The factors led to the Waterfall Model of software development 10 10 5  10/4/21 The Waterfall Model 11 11 Discussion of the Waterfall Model The waterfall model is a heavyweight process with full documentation of each process step Avantages: Separation of tasks Process visibility Quality Control at each step Cost monitoring at each step Disadvantages: In practice, each stage in the process reveals new understanding of the previous stages, which often requires the earlier stages to be revised 12 12 6  10/4/21 Discussion of the Waterfall Model The Waterfall model is not flexible enough! 13 13 Discussion of the Waterfall Model A pure sequential model is not possible The plan must allow for some form of iteration Examples: Does the Feasibility Study can create a proposed budget and schedule? Detailed design and implementation reveal gaps in the requirements specification What if the client changes requirements or what if the development team decides to change the technology? 14 14 7  10/4/21 Modified Waterfall Model 15 15 When to use the Modified Waterfall model The Modified Waterfall Model works best when the requirements are well understood and the design is straightforward For example: Converting a manual data processing systems where the requirements were well understood New version of a system where the functionality is closely derived from an earlier product Portions of a large system where some components have clearly defined requirements and are clearly separated from the rest of the system 16 16 8  10/4/21 Discussion Consider the following case study: A web-based banking application has been developed for two groups of users: personal user and enterprise user of the bank X. Now, the bank desired to develop a mobile application for personal user. They apply the modified waterfall model. Give at least 3 reasons why the modified waterfall model is appropriate in this case study. 17 17 Iterative Refinement Concept: Requirements are hard to understand until there is an operational system, particularly with user interfaces. System and program design may benefit from prototypes Process: Create a prototype system early in the development process Review the prototype with clients and test it with users, to improve the understanding of the requirements clarify the design Refine the prototype in a series of iterations. 18 18 9  10/4/21 Iterative refinement: an example (1) Problem: Add graphics package to a programming environment Requirements: The client was unsure of several important requirements E.g., syntax for how to manage coordinates across different objects Process Build a prototype version with a preprocessor and preliminary run-time package Have several iterations of development The final iteration is the complete version of package 19 19 Iterative refinement: an example (2) Problem: Add graphics package to a programming environment Requirements: The client was unsure of several important requirements E.g., syntax for how to manage coordinates across different objects Process For each iteration: Test the system with users Make modifications Repeat until users are pleased with function 20 20 10  10/4/21 Iterative Refinement - Schema 21 21 Discussion of Iterative Refinement This is a medium weight process with documentation created during the process Iterative refinement uses various techniques that enable the client to review the planned system early during development: User interface mock-ups Throw-away software components Rapid prototyping Successive refinement 22 22 11  10/4/21 User interface mock-up 23 23 Throw-away Prototyping 24 24 12  10/4/21 Evolutionary Prototyping 25 25 Get something working as quickly as possible, for client and user evaluation...but do not release it 26 26 13  10/4/21 Incremental Development 27 27 Incremental Development - Example Ecommerce website Search, Product Information, Shopping Basket, Checkout, Favourites, Customer Review 1 increment = 1 release 28 28 14  10/4/21 Incremental Development - Example 3 incrementals: 1st: 1st release 29 29 Incremental Development - Example 3 incrementals: 2nd: 2nd release 30 30 15  10/4/21 Incremental Development - Example 3 incrementals: 3rd: 3rd release 31 31 Incremental Development - Discussion Is incremental model also an iterative one? 32 32 16  10/4/21 Incremental vs. Iterative Can you see the difference? 33 Spiral Development Iterative and incremental model with more emphasis placed on risk analysis 4 main phases: Planning – Design – Construct – Evaluation An iteration = A spiral 34 34 17  10/4/21 Spiral Development - Schema 1st quadrant: Requirements are gathered and analyzed at the start of every spiral 2nd quadrant: All proposed solutions for identified problems are evaluated. Risks are identified for the selected solution, then are resolved using the best possible strategy. Prototype is built for the best possible solution 35 35 Spiral Development - Schema 3rd quadrant: identified features are developed and verified through testing Next version of the system is available 4th quadrant: customers evaluate the so far developed version Planning for the next phase then is started 36 36 18  10/4/21 Spiral Development – Risk Handling Risk: any situation that might affect the successful completion of the project Spiral model emphasizes risk handling by developing a prototype After some iterations, most of risks are studied and resolved For example: What is the risk involved in accessing data from a remote database system? What if the data access might be too slow? Risk solution: Building a prototype of the data access subsystem 37 37 Spiral model viewed as a Meta-model The spiral model subsumes all the other models Single loop represents the waterfall model Prototyping approach is used to first draft the solution before embarking on the actual product Iterations along the spiral model can be considered as the evolutionary levels through which the complete system is built At the end of each spiral, the result will typically be incorporated with the large base system 38 38 19  10/4/21 Agile Methodology Spring 2000, in Oregon, US, big question: How could speed up development times in order to bring new software to market faster? Critical milestone in the history of Agile with 3 key ideas: Speed to market Rapid feedback Continuous improvement 39 39 Agile Methodology - History Oregon 2001, Manifesto for Agile Software Development: 12 principals 40 40 20  10/4/21 Agile Approach: Iterative and Incremental 41 41 Agile Approach: Iterative and Incremental A large project is divided into small increments called sprints The development is carried out by small teams of 4 to 9 people The schedule is divided into fixed time boxes, perhaps 2 to 4 weeks Each sprint is a time box during Single sprint: requirements, which the team completes part of design, coding and testing a software project Each sprint ends with fully tested code, ready to put into production 42 42 21  10/4/21 Agile Development - Sprint After each sprint the code may be: Released (original agile method) Combined with code from other sprints for subsequent release Incorporated into a larger code base (spiral development) 43 43 Scrum – The most widely used agile method for software development 44 44 22  10/4/21 Scrum roles Scrum Master Understand the theory, practices, rules and values of Scrum Help others improve interactions to maximize the value by the Scrum team Product Owner The bridge between the business part and the technical part of the project Responsible for writing user stories and for keeping the Product backlog up to date Development Team Transform the expressed needs into usable functionalities Developers, software architects, functional analyist, graphic designers 45 45 Product Backlog 46 46 23  10/4/21 Product Backlog Contains all the userstories which will be turned into tasks so that the scrum team can select and plan in upcoming sprints PO is in charge of managing and keeping the product backlog up to date 47 47 Sprint Backlog 48 48 24  10/4/21 Epics – Userstories – Tasks Epic A functionality of the product to be developed A multiple sets of userstories grouped by categories or themes User Story Not a task, neither a specification A statement of a user expectation Task Technical activities that helps respond to user stories Tasks should be same sized but may be of different nature: design, development, test, etc. 49 49 Epics – Userstories – Tasks 50 50 25  10/4/21 Scrum Meetings 51 51 Sprint Planning – Sprint Retrospective – Daily Scrum Sprint Planning Meeting Goal: The development team selects the priority elements of the Product Backlog to complete in the current sprint Daily Stand-up Meeting Daily synchronizing meeting Goal: to enable team members to gather on a daily basis to discuss tasks and work progress as well as potential problems to overcome possible blockages to promote mutual support 52 52 26  10/4/21 Sprint Planning – Sprint Retrospective – Daily Scrum Sprint Retrospective Meeting Toward continuous improvement Take place at the end of the sprint Goal: discussing and taking a step back from the latest sprint to optimize interactions between individuals, to raise product quality to improve productivity Tools: Burnup chart Burndown chart Velocity 53 53 Scrum Development - Example 54 54 27  10/4/21 Mixed Processes In practice, many large projects use processes that mix aspects of the four types of software process Example: A project with well-understood requirements might use a modified waterfall approach to specify the requirements and system design, followed by a series of agile sprints A project with vague requirements might use iterative refinement to clarify the requirements, followed by a modified waterfall model to build the final version With spiral development, new components may be developed as a series of sprints 55 55 The most important: User Interface should be tested with users... è Iterative development, whatever process is used for the rest of the system 56 56 28  10/4/21 IT3180 Project: Iterative Refinement 57 57 IT3180 Project: Modified Waterfall Model 58 58 29  10/4/21 IT3180 Project: Agile Development 59 59 5. Software development processes (end of lecture) 60 60 30