软件工程 Software Process Models

Posted 2021-09-16 Sharon

Chapter2:software process model

Organization of processes and activities

Key points in this chapter:

1. What is software process?
2. What is software process model?
3. What are the software process models and what\'s their advantages and disadvantages and implementation area?
4. Difference between plan-driven and agile?
5. What is agile method?
6. What are the steps of software process?

• fundamental activities in software processes

  (all processes involve the following steps)

  • Specification:what the system should do
  • Design and implementation:the organization of system
  • Validation:checking if it does what the customer wants
  • Evolution:changing in response to customer need(changing requirements) development and evolution

• descriptions of activities in software process

  • Products:这一个activity结束之后会得到什么
  • Roles:哪些人需要参与到这个activity

  • Pre- and Post- conditions

    • Pre-condition:conditions that must test true before rntering this activity
    • Post-condition:conditions that must test true after exiting this activity

      (退出这个module时 如果不符合post-condition 表示这个module的coding是有错的)

• software process:a sequence of activities leading to the production of a software product.
• software process model/aka product life cycle : an abstract representation of a software process.

• software processes(des and where)

  • Plan-driven processes:Plan-driven processes are processes where all of the process activities are planned in advance and progress is measured against this plan.
  • Agile processes:In agile processes, planning is incremental and it is easier to change the plan and the software to reflect changing customer requirements.

• Kinds of software process models:

  • Waterfall model:Plan-dirven process with strict order(前一个activity结束才能进行下一个activity)

    前一个activity结束才能进行下一个activity

    5 steps in waterfall model:

    • requirements definition
    • system and software design
    • implementation and unit testing
    • integration and system testing
    • operation and maintenance

    Advantages of waterfall model

    • Helps coordinate the work
    • Good requirements imporves software quality.

    Disadvantages of waterfall model: difficult to deal with changing requirements

    Application domain of waterfall model:

    • Large system
    • requirements that are well-understood and unlikely to change radically 比如说会议室预约系统

  • Incremental model

    interleaving activities
    Advantages of incremental model:

    • dealing with change
    • repid delivery
    • effective feedbacks

    Disadvantages of incremental model:

    • invisible processes
    • degrading system structure

    Application condition of incremental model:

    • limited time and budget(incremental省时省钱)
    • changing requirements(可以随时改)

  • Reuse-oriented model

    component search and configuration

    Key points of re-use oriented model:

    • Component selection
    • Component filtering
    • Component-dependent requirements development

    Advantages of reuse-oriented model:

    • Reduce cost and risk(为什么reduce risk)
    • Faster delivery(都用别人做好的组件那肯定快）

    Disadvantages of reuse-oriented model:

    • Inevitable requirements compromises(不一定能找到非常符合要求的组件)
    • Different from real needs(同上)
    • Components out of control(组件里面的实现细节可能不知道)
  • These models are not mutually exclusive and are often used together, especially for large systems development.
  • For large systems, it makes sense to combine some of the best features of the waterfall and the incremental development models.
  • You need to have information about the essential system requirements to design a software architecture to support these requirements. You cannot develop requirements incrementally.
  • Sub-systems within a larger system may be developed using different approaches.
  • Parts of the system that are well understood can be specified and developed using a waterfall-based process.
  • Parts of the system which are difficult to specify in advance, such as the user interface, should always be developed using an incremental approach.

Agile methods(是一种理念、思想和价值观 不是具体的一种模型)

• Agile software development methods

  • Extreme programming(XP)
  • Scrum(敏捷开发)
  • Crystal
  • Adaptive software development(ASD)
  • DSDM(Dynamic Systems Development Method)
  • Feature driven development(FDD)

• Scaling agile mothods：

  • Scaling up 从一个小鱼缸换成一个大鱼缸
  • Scaling out(pipeline) 从一个小鱼缸伸一个馆子到大鱼缸