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Software Development

Software Development. By Rick Mercer with help from these sources: Rational Unified Process Computing Fundamentals with C++ , Rick Mercer Designing Object Oriented Software , Rebbeca Wirfs-Brock, Wilkerson, Wiener Object-Oriented Design Heuristics , Arthur Riel. Software Challenges.

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Software Development

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  1. Software Development By Rick Mercer with help from these sources: Rational Unified Process Computing Fundamentals with C++, Rick Mercer Designing Object Oriented Software, Rebbeca Wirfs-Brock, Wilkerson, Wiener Object-Oriented Design Heuristics, Arthur Riel

  2. Software Challenges • Specifications may be incomplete • Software product is expected to be used for a long time • Ever more complex systems, high expectations • Requirements change • We don't know what the customer wants • The customers don't know what they want

  3. One Approach:Waterfall • Software go through several stages called the life cycle • Waterfall model

  4. Waterfall Model

  5. Waterfall Model (con.) • Waterfall has some severe problems. • The team has to be almost clairvoyant little room for error • places the high risk and difficult elements towards the end • Craig Larman's book[1] provides proof that waterfall has proved to be a terrible way to develop software. • In a two-study, 87% of all investigated projects failed • The waterfall process was the "single largest contributing factor for failure, being cited in 82% of the projects as the number one problem." • Rick will now attempt to tell a joke [1] Agile and Iterative Development: a Manager's Guide, Addison-Wesley Professional, 2003

  6. Iterative Software Development • An iteration is a small part of the entire system

  7. Rational Unified Process • Practices of RUP • Develop iteratively • Manage changing requirements • Use components such as Java classes • Visually Model with UML • Continuously test • RUP allows you to select from many processes http://www-306.ibm.com/software/awdtools/rup/

  8. A Process we'll use • Agile Manifesto See http://agilemanifesto.org/ • Started with Scrum and XP (Kent Beck’s eXtreme Programming), mid 1990s • Teams often choose from a set of practices • A few Agile practices we are or will be using • Planning game: stories, estimation, iterations • Test Driven Development (TDD) • Pair Programming • Continuous Integration • Sustainable Pace (determine velocity would be nice) • Coding Style (use the same style as team whether you like it or not) • On-site customer (simulated)

  9. Responsibility Driven Design Responsibility Driven Design, Rebecca Wirfs Brock, 1990The Coffee Machine Design Problem, Alistair Cockburn, C/C++ User's Journal, May and June 1998. Introducing Object-Oriented Design with Active Learning, Rick Mercer , Consortium for Computing in Small Colleges, 2000

  10. In Rebecca Wirfs Brocks' Words • Responsibility-Driven Design is a way to design that emphasizes behavioral modeling using objects, responsibilities and collaborations. In a responsibility-based model, objects play specific roles and occupy well-known positions in the application architecture. Each object is accountable for a specific portion of the work. They collaborate in clearly defined ways, contracting with each other to fulfill the larger goals of the application. By creating a "community of objects", assigning specific responsibilities to each, you build a collaborative model of our application.Responsible: able to answer for one's conduct and obligations—trustworthy, Merriam Webster

  11. Responsibility Driven DesignSummarizing Rebecca in Rick's words 1) Identify candidate objects that model a system as a sensible set of abstractions 2) Determine the responsibility of each object • what an instance of the class must be able to do, • and what each instance must know about itself 3) Understand the system through role play • To help complete its responsibility, an object often needs help from other objects

  12. OO Design Principle • The Single Responsibility Principle Classes should have a single responsibility http://en.wikipedia.org/wiki/Single_responsibility_principle • Why? • Cohesion, when high, reduces complexity, makes the system more understandable http://en.wikipedia.org/wiki/Cohesion_%28computer_science%29 • Maintenance: Fixing or changing a module should not break other parts of the system

  13. First Design a ModelNote: design is iterative • Find a set of objects (candidate classes) that model a solution • Each will be a part of the bigger system • Each should have a single responsibility • What are these objects?

  14. Find the Objects • Candidate objects may come from • The nouns in the problem statement • Underline the noun phrasesto look for the objects that could model the system • An understanding of the problem domain • knowledge of the system that the problem specification may have missed or took for granted • The words floating around the room Alistair Cockburn

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