Lecture02_SDLC.pdf

IT1060 - Software Process Modeling SOFTWARE PROCESS MODELING Software Development Life Cycles 1 SLIIT - Faculty of Computing IT 1060 Group an...

IT1060 - Software Process Modeling SOFTWARE PROCESS MODELING Software Development Life Cycles 1 SLIIT - Faculty of Computing IT 1060 Group and Topic Allocation- Assignments- 2024 Group registration link will be published on the first-year supportive page. Students should form a group with five members and the Group leader should register a group. Once students registered groups, Topic allocation will be done randomly Then, Topic allocation will be published on the first- year supportive page. 2 SLIIT - Faculty of Computing IT 1060 Session Outcomes What is a Software Process SDLC Life Cycle Model Life Cycle Models Waterfall Model Prototyping Model Incremental Model Spiral Model Comparison and Selection SLIIT - Faculty of Computing IT 1060 What is an Engineering Process? SLIIT 4 SLIIT - Faculty of Computing IT 1060 What is a Software Development Process? A set of Activities and Associated Results that produce a Software. SLIIT - Faculty of Computing IT 1060 Fundamental Process Activities 1. Software Specification 2. Software Development 3. Software Validation 4. Software Evolution SLIIT 6 SLIIT - Faculty of Computing IT 1060 1. Software Specification Specification involves clearly documenting the expectations on the system to be built Lays out requirements, and may include written and diagrammatic description of the services that the future system must provide. SLIIT 7 SLIIT - Faculty of Computing IT 1060 2. Software Development Software development involves designing and implementing the system according to the software specification SLIIT 8 SLIIT - Faculty of Computing IT 1060 3. Software Validation Software validation involves checking and verifying whether the system fulfills the requirements. SLIIT 9 SLIIT - Faculty of Computing IT 1060 4. Software Evolution Software needs to be changed and upgraded with time. SLIIT 10 SLIIT - Faculty of Computing IT 1060 What is a SDLC? The Software Development Life Cycle (SDLC) is a framework that defines activities performed throughout the software development process SLIIT - Faculty of Computing IT 1060 Life Cycle Model (Process Model) A software life cycle (process) model: is a descriptive and diagrammatic model of the life cycle of a software product; identifies all the activities and phases necessary for software development; establishes a precedence ordering among the different activities. Life cycle models encourage systematic and disciplined software development. SLIIT 12 SLIIT - Faculty of Computing IT 1060 Life Cycle Models Traditional Approaches 1. Waterfall Model 2. Incremental Model 3. Prototyping Model 4. Spiral Model 5. Unified Process Modern Approaches Agile Methods (XP, Scrum) Secure Software Development SLIIT - Faculty of Computing IT 1060 Life Cycle Models SLIIT - Faculty of Computing IT 1060 1 Waterfall Model SLIIT - Faculty of Computing IT 1060 Waterfall Model SLIIT - Faculty of Computing IT 1060 Waterfall model Waterfall model is the most well known SDLC. It is very simple to understand and use. Each phase begins only after the previous phase is over. Also called Linear Model A document driven process This model specifies what the system is supposed to do (i.e. define the requirements) before building the system (i.e. designing) SLIIT - Faculty of Computing IT 1060 1. Feasibility Study This is the first phase of any SDLC model. The project objective is determined during this phase. The client and company developing the software decide if they should ; Keep the existing system as is, or Build a new software SLIIT - Faculty of Computing IT 1060 Why do a feasibility study? To provide management with enough information to know: Whether the project can be done Whether the final product will benefit its users What the alternative solutions are Whether there is a preferred alternative SLIIT - Faculty of Computing IT 1060 Example – Library System What are the feasibility criteria for a ‘Library System’? SLIIT - Faculty of Computing IT 1060 2. The Requirements Phase Aim: to understand the customer’s requirements: A customer may be a single person, a group, a department, or an entire organization: This phase involves two distinct activities: 1. Requirements Gathering and Requirements Analysis 2. Requirements Specification SLIIT 21 SLIIT - Faculty of Computing IT 1060 2a.1 Requirement Gathering The goal of this phase is for the stakeholders to find out the ‘what to be done’. Questions answered during this phase include: Who will use the system? How will they use the system? What will be the input for the system? What will be the output from the system? Requirement Gathering involve collecting information through meetings, interviews and discussions SLIIT - Faculty of Computing IT 1060 2a.2 Requirements Analysis Aim: To understand exactly what the customer needs.. which may not be what they ask for: data to be input to the system; processing to be performed on these data; data to be output from the system; characteristics of the system as a whole; constraints on the system/project. WHAT, not HOW! SLIIT 23 SLIIT - Faculty of Computing IT 1060 2b Requirements Specification Requirements are documented in a Software Requirements Specification (SRS). The SRS forms the basis of a legal contract with the customer: Software Engineers who specialize in requirements gathering, analysis, and specification are called (Systems/ Business / Requirement) Analysts. SLIIT 24 SLIIT - Faculty of Computing IT 1060 3. Design Architects and Designers craft a high-level and low level design of the software. Architectural Design Low level Design Decisions are made about hardware, software and the system architecture. A design specification document (DSD) records this information. SLIIT - Faculty of Computing IT 1060 4. Development On receiving system design documents, the work is divided in modules. A set of developers code the software as per the established design specification, using a chosen programming language Programmers carry out some program testing to discover faults in the program and remove these faults in the debugging process SLIIT - Faculty of Computing IT 1060 5. Testing The testing phase ensures that the software requirements are in place and that the software works as expected. When a defect is identified, testers inform the developers. If the defect is valid, developers resolve it and create a new version of the software which then repeats the testing phase. The cycle continues until all defects are mitigated and the software is ready for deployment into the production environment. SLIIT - Faculty of Computing IT 1060 6. Deployment and Maintenance. Once the software is error free, it is deployed into the operating environment. While the customers are using the software, any issues will be brought to the attention of the maintenance team They work to resolve them immediately. SLIIT - Faculty of Computing IT 1060 Waterfall in practise SLIIT - Faculty of Computing IT 1060 Waterfall Model - Strengths Simple and easy to manage– each phase has specific deliverables. Milestones are better understood Sets requirements stability Works well for smaller projects where requirements are very well understood. A schedule can be set with deadlines. SLIIT - Faculty of Computing IT 1060 Waterfall Model - Weaknesses No working software is produced until end. High uncertainty. Delays discovery of serious errors. After requirements phase, there is no formal way to make changes to the requirements. Not a good model for complex projects projects where requirements are at a moderate to high risk of changing SLIIT - Faculty of Computing IT 1060 When to use Waterfall Model Software requirements clearly defined and known Product definition is stable New version of the existing software system is created Software development technologies and tools are well known Ample resources with required expertise are available SLIIT - Faculty of Computing IT 1060 2 Iterative Model SLIIT - Faculty of Computing IT 1060 Iterative Waterfall Model The classical waterfall model is idealistic: It assumes that no defects are introduced during any of the development phases. In practice, defects are introduced during every phase of the software life cycle: Hence feedback paths must be added to the classical waterfall model. The resulting Iterative Waterfall Model is one of the most widely used process models…. SLIIT 34 SLIIT - Faculty of Computing IT 1060 Iterative Waterfall Model SLIIT 35 SLIIT - Faculty of Computing IT 1060 Iterative Waterfall Model Strengths Defects are detected and fixed early through the feedback path Weaknesses Limited customer interactions Difficult to incorporate change requests SLIIT 36 SLIIT - Faculty of Computing IT 1060 3 Incremental Model SLIIT - Faculty of Computing IT 1060 What is the OS you work on? 38 SLIIT - Faculty of Computing IT 1060 Incremental model Incremental model is an evolution of waterfall model. The product is designed, implemented, integrated and tested as a series of incremental builds. The incremental model prioritizes requirements of the system and then implements them in groups. It is the process of constructing a partial implementation of a total system and slowly adding increased functionality or performance. SLIIT - Faculty of Computing IT 1060 Incremental model SLIIT - Faculty of Computing IT 1060 Incremental model - Strengths Generates working software quickly and early during the software life cycle. More flexible - less costly to change scope and requirements. Easier to test and debug. Easier to manage risk. Lowers initial delivery cost. Less stress for the development team. SLIIT - Faculty of Computing IT 1060 Incremental model - Weaknesses Requires good planning and design Each phase of an iteration is rigid and do not overlap each other. Demarcation of increments can be difficult in a practical application. Total cost of the system might not be lower. Problems may arise pertaining to system architecture because not all requirements are gathered up front for the entire software life cycle. SLIIT - Faculty of Computing IT 1060 When to use Incremental model On projects which have lengthy development schedules A need to get basic functionality to the market early Most of the requirements are known up- front but are expected to evolve over time On a project with new technology SLIIT - Faculty of Computing IT 1060 Mini-Case 1 The project is to develop an inventory control system for a new super market in town. It should have all the regular functionalities such as adding new stocks, getting reports such as inventory re- order report and daily sales report etc. A project team has previous experience developing inventory systems for other clients. SLIIT - Faculty of Computing IT 1060 4 Prototyping Model SLIIT - Faculty of Computing IT 1060 Farming Software 46 SLIIT - Faculty of Computing IT 1060 Explain Whatsapp (before implementation) to a traditional farmer 47 SLIIT - Faculty of Computing IT 1060 Prototype Model Instead of freezing the requirements before coding or design, a prototype is built to clearly understand the requirements. This prototype is built based on the current requirements. Through examining this prototype, the client gets a better understanding of the features of the final product. Requirements may be changed with the client feedback on the prototype. SLIIT - Faculty of Computing IT 1060 Prototype Model SLIIT - Faculty of Computing IT 1060 Prototyping Model - Strengths Ability to clarify user’s expectations for the system to be developed Prototype stimulates awareness of additional needed functionality Better user satisfaction Early user feedback SLIIT - Faculty of Computing IT 1060 Prototyping Model - Weaknesses Scope Creep - The system scope may expand beyond original plans. Overall maintainability may be overlooked. The customer may want the prototype be delivered. Process may continue forever SLIIT - Faculty of Computing IT 1060 When to Use Prototyping Requirements are unstable or have to be clarified Many user interfaces New technology New, original development Developers are not familiar with the technical and development tools SLIIT - Faculty of Computing IT 1060 Selection of Approach YES Incremental Early YES Release? Requirements NO Waterfall Defined? NO Prototyping SLIIT - Faculty of Computing IT 1060 Question A company is developing an advanced version of their current software available in the market, what model approach would they prefer ? a) Waterfall b) Incremental c) Prototyping SLIIT - Faculty of Computing IT 1060 Question Selection of a model is based on…? a) Requirements b) Development team c) Users d) Project type and associated risk e) All of the mentioned SLIIT - Faculty of Computing IT 1060 SDLC Model Selection Is based on 1. Customer a) Budget b) Timeline c) Existing software/ OSS d) Client experience and technical knowledge e) Flexibility 2. Product a) Complexity and risk level b) New / experienced technology c) Availability of tools d) Requirements Clarity 3. Developer experience and technical knowledge …….. 56 SLIIT - Faculty of Computing IT 1060 5 Spiral Model SLIIT - Faculty of Computing IT 1060 Spiral Model Meta Model - combines iterative and prototype development with the systematic, controlled aspects of the waterfall model. Allows for incremental releases Introduced by Barry Boehm in 1986. Allows elements of the product to be added in when they become available or known. Emphasises on risk management SLIIT - Faculty of Computing IT 1060 Spiral Model SLIIT - Faculty of Computing IT 1060 Spiral Model Quadrant 1: Planning Determine objectives, alternatives, and constraints. Quadrant 2: Risk Analysis Evaluate alternatives, identify, resolve risks. Quadrant 3: Development & Test Develop, verify, next-level product. Quadrant 4: Evaluation Analyse feedback and plan next phases. SLIIT - Faculty of Computing IT 1060 Spiral Model SLIIT - Faculty of Computing IT 1060 Detailed Spiral 62 SLIIT - Faculty of Computing IT 1060 Question Which of the following models will not be able to give the desired outcome if user’s participation is not involved? a) Waterfall b) Spiral c) Prototyping SLIIT - Faculty of Computing IT 1060 Spiral Model - Strengths Focus on risk analysis. Good for large and mission critical projects A working software is produced early The design does not have to be perfect Early and frequent feedback from users Cumulative costs assessed frequently SLIIT - Faculty of Computing IT 1060 Spiral Model - Weaknesses Can be a costly model to use. Risk analysis requires expertise. Success is highly dependent on the risk analysis phase. Doesn’t work well for smaller projects. SLIIT - Faculty of Computing IT 1060 When to use Spiral Model For medium to high-risk projects New technology to be used Complex, constantly changing and continuous Requirements Significant changes are expected (research and exploration) Users are unsure of their needs SLIIT - Faculty of Computing IT 1060 Question Which of the following life cycle model can be chosen if the development team has less experience on similar projects? a) Spiral b) Waterfall d) Iterative SLIIT - Faculty of Computing IT 1060 Activities Which life cycle is suitable? SLIIT - Faculty of Computing IT 1060 Mini-Case 2 A library management system is required for a National Library with a number of branches in many cities. System should link to a number of other online libraries, databases, journals and university libraries through web and manage different user subscriptions. The project team has little experience in developing library systems before. However there is not much pressure on time. SLIIT - Faculty of Computing IT 1060 Mini-Case 3 A Project is to develop a complete system for a new bank. System will have many users, interrelationships, and functions. The project has few risks related to requirements definition. These risks needs to be reduced. SLIIT - Faculty of Computing IT 1060 Waterfall V-Shaped Evolutionary Spiral Iterative and Agile Prototyping Incremental Unclear User Poor Poor Good Excellent Good Excellent Requirement Unfamiliar Poor Poor Excellent Excellent Good Poor Technology Complex System Good Good Excellent Excellent Good Poor Reliable system Good Good Poor Excellent Good Good Short Time Poor Poor Good Poor Excellent Excellent Schedule Strong Project Excellent Excellent Excellent Excellent Excellent Excellent Management Cost limitation Poor Poor Poor Poor Excellent Excellent Skills limitation Good Good Poor Poor Good Excellent Documentations Excellent Excellent Good Good Excellent Poor Component Excellent Excellent Poor Poor Excellent Poor reusability SLIIT - Faculty of Computing IT 1060 References I. Sommerville, Software Engineering, 10th ed., Addison-Wesley, 2011. – Chapter 2 Roger Pressman, Software Engineering: A Practitioner’s Approach – Chapter 2 72 SLIIT - Faculty of Computing IT 1060 Next Lecture Requirements Engineering 73 SLIIT - Faculty of Computing