Mithat Konar

• Ghezzi, Carlo, Mehdi Jazayeri, and Dino Mandrioli. “Software Engineering Principles.” In Fundamentals of Software Engineering. 2nd ed. Upper Saddle River, N.J.: Prentice Hall, 2003. 41-66.

• Motivation
  • Most real-world problems are:
    • Complex, difficult to decompose
    • Involve a number of developers
    • Evolve over time
  • Software engineering attempts to provide developers with strategies to manage this.
  • “How do you build big projects?”

• Product: “What it is,” and “The code you write.”
• Process: How you got there.
• Both are important.

Principles → methods and techniques → methodologies → tools

• Rigor and formality
• Modularity
• Separation of concerns
• Abstraction
• Anticipation of change
• Generality
• Incremantality

• rigor: the quality or state of being very exact, careful, or strict¹⁾
• formality: the highest degree of rigor
  • Often based on mathematical/logical laws
• Tools include natural language, formal languages
• Different projects/parts require more or less rigor/formality
  • High criticallity → high rigor/formality

• Impacts s/w qualities of:
  • reliability
  • verifiability
  • maintainability
  • reusability
  • portability
  • understandability
  • interoperability
• Impacts process quality of reusability

• Features and responsibilities should overlap as little as possible.
• Minimizes interdependence
• Increases resusabilty
• Can be applied to product and process
• Example: A lamp is not a toaster.
  • Changing a light bulb doesn't break toasting.
  • If you need a lamp someplace, you don't have to get a toaster as well.

• Another example: the Web
  • “Web 1.0”: content, presentation, behavior comingled in same HTML code

    <a href="foo.html"><font
      face="verdana" color="green" 
      target="_foowindow">Click me!</font></a>

  • “Web 2.0+”:
    • Content/semantics: XHTML
    • Presentation: CSS
    • Behavior: Javascript
    • code

• Divide the system into smaller modules
• Typically results it a tree of modules and submodules
• Decomposition: recursively subdividing the system
  • “Divide and conquer”
  • top-down
• Composition: building up from completed parts
  • Legos
  • bottom up

• Benefits
  • Facilitates separation of concerns
  • Supports anticipation of change
  • Enhances quality of understandability

• Abstraction in general use means the act or process “[considering] apart from application to or association with a particular instance.”²⁾
• In S/W Engineering, abstraction means wrapping a concept such that it:
  • Expresses the concept only in terms of what is relevant.
  • Shields the user from everything that's not relevant.
  • (i.e., building models)
• Examples:
  • What is a ball?
  • Functions

• Humans are powerful abstractors.
• Abstraction is at the heart of computing.
• Applied to:
  • Hardware
  • Programming languages
  • Program design
  • Programming process
  • …

• Almost all development projects change
  • while the project is being developed,
  • after release.
• Process and code should be designed to support evolution.

• Often, a problem you work on is a more specific version of a more general problem.
• Work with solution based on more general problem.
  • If you need to invent an oxcart wheel, first invent a wheel and use that to build your oxcart wheel.
  • Don't re-invent the wheel if you don't need to.
  • General problem might be easier to solve (or not).
• Supports quality of reuse.

• A journey of a thousand miles begins with a single step.³⁾
• Development proceeds in a stepwise fashion (i.e., in increments)
• Strategies:
  • Deliver subsets of a system early to get early feedback
  • Deliver prototype of the system and incrementally add effort to turn it into product
  • Implement functionality, then tune performance
  • “Iterative refinement”
• Supports anticipation of change
• Example: Adium's commit history

• Different methodologies emphasize different combinations of principles
• Conflicts among principles may arise.
• New field and subject to change.
• Made by humans for humans.
  • Your contemplations and considerations are crucial.

¹Microsoft, Inc. “Version Class (System).” MSDN | Microsoft Development, Subscriptions, Resources, and More. http://msdn.microsoft.com/en-us/library/system.version.aspx#Y171 (accessed March 9, 2011).
²Ibid. Emphasis added.

This content is Copyright © 2012 Mithat Konar