CS 451 Software Engineering Winter Term Yuanfang Cai Room 104, University Crossings 215.895.0298 yfcai@cs.drexel.edu 1 Drexel University
PROCESS MODEL A structured collection of practices Describe characteristics of effective process CMMI is not a process CMMI describes the characteristics of effective processes 2 Drexel University
Prescriptive Models 3 Drexel University
PRESCRIPTIVE MODELS Regardless of the model, all models contain the following components: communication planning modeling construction deployment Which of these phases do you think is most difficult and in what situations? 4 Drexel University
PROCESS MODELS What do you think the most popular process model is? Waterfall Incremental Evolutionary Formal 5 Drexel University
PROCESS MODELS – WATERFALL The “Classic Life Cycle”, The “Textbook Cycle” A systematic, sequential approach with the following steps: Customer Specification of Requirements (Communication) Planning (Estimating, Scheduling, Tracking) Modeling (Analysis and Design) Construction (Code and Test) Deployment (Delivery, Support, and Feedback) 6 Drexel University
PROCESS MODELS – WATERFALL The book calls the first phase communication. I do not like this definition as communication must occur at all stages. 7 Drexel University
PROCESS MODELS – WATERFALL When is the waterfall process model appropriate? In a purest sense, probably never. I have never worked on a project that follows a completely linear progression. However, the waterfall process is appropriate if followed in spirit if not the letter of the model in some situations: Well defined projects Projects with no technology risks Well defined domains Stable requirements 8 Drexel University
PROCESS MODELS – WATERFALL Why is it difficult to follow? Hard to follow a strictly sequential path. Customers have difficulty stating ALL the requirements explicitly Customers business model changes during the course of developing the application Customers are required to have patience, since a working program is not available until very late in the process. 9 Drexel University
PROCESS MODELS – INCREMENTAL PROCESS MODEL Even with well defined projects, a linear approach is often difficult. Additionally, sometimes a portion of the software needs to be delivered early. The incremental model combines elements of the waterfall model applied in an iterative fashion. Incremental model delivers an operational product with each increment. Works well for project resource management (staffing). 10 Drexel University
PROCESS MODELS – INCREMENTAL PROCESS MODEL 11 Drexel University
PROCESS MODELS – EVOLUTIONARY PROCESS MODEL - PROTOTYPING Customers define general objectives, but does not identify the details. Often, the customer doesn’t know what they want the system to look like. A repeating cycle of the following steps include: Communication Quick Plan Modeling Quick Design Construction of Prototype Deployment & Feedback 12 Drexel University
PROCESS MODELS – EVOLUTIONARY PROCESS MODEL - PROTOTYPING Depending upon the complexity I recommend a first pass with “Paper Prototypes”. “Paper” can be virtual with mockups of the application being developed in either a development environment like Visual Studio or even HTML. Second pass could be a semi functional application with no data connectivity. 13 Drexel University
PROCESS MODELS – EVOLUTIONARY PROCESS MODEL - PROTOTYPING Third pass for the developers to try any unknown technical issues. Often good for these prototypes to be used for requirements gathering and to reduce technology risks. Best if the prototype is a throw-away. One good reason to develop your prototype in a different language/system than the final project 14 Drexel University
PROCESS MODELS – EVOLUTIONARY PROCESS MODEL - PROTOTYPING Drawbacks: Customers like the prototype and want to place it in production. Developers forget the design decisions and their mistakes leak into the production system. 15 Drexel University
PROCESS MODELS – EVOLUTIONARY PROCESS MODEL – SPRIAL MODEL An evolutionary software model that couples the iterative nature of prototyping with the controlled and systematic aspects of the waterfall model. This is true, but with one addition: risk analysis. At each cycle through the spiral, milestones are achieved and risk is reevaluated. 16 Drexel University
PROCESS MODELS – EVOLUTIONARY PROCESS MODEL – SPRIAL MODEL 17 Drexel University
PROCESS MODELS – EVOLUTIONARY PROCESS MODEL – SPRIAL MODEL Most developers lean towards evolutionary process models. They have inherent problems: Prototyping and similar evolutionary models are hard to plan, thus hard to estimate, thus hard to contract. How many cycles will there be? Speed of evolution is difficult to dictate Is the third statement true? Why is this a goal? 18 Drexel University
PROCESS MODELS – SPECIALIZED PROCESS MODEL FORMAL METHODS MODEL The Formal Methods Model encompasses a set of activities that leads to formal mathematical specification of computer software. In theory, the following is reduced when using formal methods: Ambiguity Incompleteness Inconsistency Do you agree? 19 Drexel University
PROCESS MODELS – SPECIALIZED PROCESS MODEL FORMAL METHODS MODEL Drawbacks: The development of formal models is currently quite time consuming and expensive Few software developers have the background, thus extensive training is required. (is training viable? COBOL -> OOP) Difficult to use formal model to communicate with a non- technical customer. Forest and Trees. Useful for safety critical application or anywhere failure is highly costly. 20 Drexel University
Agile Development 21 Drexel University
Manifesto Value individuals and interactions over processes and tools Value working software over comprehensive documentation Value customer collaboration over contract negotiation Value responding to changes over following a plan 22 Drexel University
AGILE ≠ HACK OUT SOLUTONS! A process is required Discipline is essential 12 principles 23 Drexel University
Agile Principles Our highest priority is to satisfy the customer 1. through early and continues delivery of valuable software. Welcome changing requirements, even late in 2. development. Agile processes harness change for the customer’s competitive advantage. Deliver working software frequently, from a 3. couple of weeks to a couple of months, with a preference to the shorter timescale 24 Drexel University
Agile Principles Business people and developers must work 4. together daily throughout the project. Build projects around motivated individuals. 5. Given them the environment and support they need, and trust them to get the job done. The most efficient and effective method of 6. conveying information to and within a development team is face-to-face conversation. Working software is the primary measure of 7. progress. 25 Drexel University
Agile Principles Agile processes promote sustainable 8. development. The sponsors, developers and users should be able to maintain a constant pace indefinitely. Continuous attention to technical excellence 9. and good design enhances agility. 10. Simplicity---the art of maximizing the amount of work not done---is essential 11. The best architectures, requirements, and designs emerge from self-organizing teams 26 Drexel University
Agile Principles 12. At regular intervals, the team reflects on how to become more effective, then tunes and adjusts its behavior accordingly. 27 Drexel University
AGILE PROCESS MODELS Each has a set of “ideas” that represent a significant departure from conventional software engineering. Are the agility ideas really new? 28 Drexel University
Agile Process Models Agile Unified Process (AUP) Dynamic Systems Development Method (DSDM) Essential Unified Process (EssUP) Extreme Programming (XP) Feature Driven Development (FDD) Open Unified Process (OpenUP) Scrum Velocity tracking 29 Drexel University
EXTREME PROGRAMMING Planning User stories Values Acceptance test criteria Iteration plan Design Simple design CRC cards Spike solutions prototypes 30 Drexel University
EXTREME PROGRAMMING Coding Pair programming Refactoring Test Unit test Continuous integration Acceptance testing Release Software increment 31 Drexel University
EXTREME PROGRAMMING 32 Drexel University
EXTREME PROGRAMMING 33 Drexel University
EXTREME PROGRAMMING 34 Drexel University
EXTREME PROGRAMMING 35 Drexel University
Summary Prescriptive Models Waterfall Incremental Evolutionary Agile 36 Drexel University
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