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====== Principles of Software Engineering ======
Mithat Konar\\ 
July 24, 2012

===== Adapted from =====
[[http://www.pearsonhighered.com/pearsonhigheredus/educator/product/products_detail.page?isbn=0133056996|{{:century:fundamentals-swe-cover.jpg?150 |}}]]Ghezzi, Carlo, Mehdi Jazayeri, and Dino Mandrioli. "[[http://www.pearsonhighered.com/pearsonhigheredus/educator/product/products_detail.page?isbn=0133056996|Software Engineering Principles]]." In //Fundamentals of Software Engineering//. 2nd ed. Upper Saddle River, N.J.: Prentice Hall, 2003. 41-66.

===== Introduction =====
  * Motivation
    * Most real-world problems are:
      * Complex, difficult to decompose
      * Involve a number of developers and other shareholders
      * Evolve over time
    * Software engineering attempts to provide developers with strategies to manage this.
    * //"How do you build big projects?"//

===== Introduction =====
  * //Product//: "What it is," and "The code you write."
  * //Process//: How you got there
  * Both are important

===== Introduction =====
{{:century:priciples_hierarchy.png?450 |From Ghezzeri, et al. (footnote 1)}}
 \\
 ↑\\
 changes rapidly\\
 changes slowly\\
 ↓

===== The principles =====
  * Rigor and formality
  * Separation of concerns
  * Modularity
  * Abstraction
  * Anticipation of change
  * Generality
  * Incremantality

===== The principles =====
  * **Rigor and formality**
  * Separation of concerns
  * Modularity
  * Abstraction
  * Anticipation of change
  * Generality
  * Incremantality

===== Rigor and formality =====
  * **rigor**: the quality or state of being very exact, careful, or strict.<sup>[[http://www.learnersdictionary.com/search/rigor|2]]</sup>
  * **formality**: the highest degree of rigor
    * Often based on mathematical/logical laws
  * Different projects/parts require more or less rigor/formality
    * High criticality -> high rigor/formality
  * Tools include natural language, formal languages

===== Rigor and formality =====
  * Impacts software qualities of:
    * reliability
    * verifiability
    * maintainability
    * reusability
    * portability
    * understandability
    * interoperability
    * reusability

===== The principles =====
  * Rigor and formality
  * **Separation of concerns**
  * Modularity
  * Abstraction
  * Anticipation of change
  * Generality
  * Incremantality

===== Separation of concerns =====
  * 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.

===== Separation of concerns =====
  * Another example: the Web
    * "Web 1.0": content, presentation, behavior comingled in same HTML code<code html><a href="foo.html"
target="_foowindow"><font-face="verdana"
color="green">Click me!</font></a></code>
    * "Web 2.0+":
      * Content/semantics: XHTML
      * Presentation: CSS
      * Behavior: Javascript
      * [[separation of concerns example|example code]]

===== The principles =====
  * Rigor and formality
  * Separation of concerns
  * **Modularity**
  * Abstraction
  * Anticipation of change
  * Generality
  * Incremantality

===== Modularity =====
  * Division of the system into smaller //modules//
  * //Decomposition//: recursively subdividing the system 
      * "Divide and conquer"
      * //top-down//
  * //Composition//: building up from completed parts
    * Legos
    * //bottom up//

===== Modularity =====
  * Benefits:
    * Facilitates **separation of concerns**
    * Supports **anticipation of change**
    * Enhances quality of //understandability//

===== The principles =====
  * Rigor and formality
  * Separation of concerns
  * Modularity
  * **Abstraction**
  * Anticipation of change
  * Generality
  * Incremantality

===== Abstraction =====
  * In general use: considering something "apart from application to or association with a particular instance."<sup>[[http://www.merriam-webster.com/dictionary/abstracting?show=0&t=1343046707|3]]</sup>
  * In S/W Engineering: 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

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

===== The principles =====
  * Rigor and formality
  * Separation of concerns
  * Modularity
  * Abstraction
  * **Anticipation of change**
  * Generality
  * Incremantality

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

===== The principles =====
  * Rigor and formality
  * Separation of concerns
  * Modularity
  * Abstraction
  * Anticipation of change
  * **Generality**
  * Incremantality

===== Generality =====
  * 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:
    * Invent a wheel and then use that to build the oxcart wheel.
    * Don't re-invent the wheel in the first place.
  * General problem might be easier to solve (or not).
  * Supports quality of reuse

===== The principles =====
  * Rigor and formality
  * Separation of concerns
  * Modularity
  * Abstraction
  * Anticipation of change
  * Generality
  * **Incremantality**

===== Incremantality =====
  *//A journey of a thousand miles begins with a single step.// ---Lao-tzu mistranslation<sup>[[http://www.quotationspage.com/quote/24004.html|4]]</sup>
  * Development proceeds in a stepwise fashion (i.e., in //increments//).
    * "Iterative refinement"
    * 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
  * Supports **anticipation of change**
  * Example: [[http://adium.im|Adium]]'s [[https://bitbucket.org/adium/adium/changesets|commit history]]
  
===== Concluding remarks =====
  * Different methodologies emphasize different combinations of principles.
  * Conflicts among principles may arise.
  * Software engineering is:
    * a new field and subject to change.
    * made by humans for humans.
  * Your contemplations and contributions are crucial.

===== Endnotes =====
<sup>1</sup>Ghezzi, Carlo, Mehdi Jazayeri, and Dino Mandrioli. "[[http://www.pearsonhighered.com/pearsonhigheredus/educator/product/products_detail.page?isbn=0133056996|Software Engineering Principles]]." In //Fundamentals of Software Engineering//. 2nd ed. Upper Saddle River, N.J.: Prentice Hall, 2003. 42.

<sup>2</sup>"Merriam-Webster's Learner's Dictionary." Merriam-Webster's Learner's Dictionary. http://www.learnersdictionary.com/search/rigor (accessed July 23, 2012).

===== Endnotes =====
<sup>3</sup>"Abstracting - Definition and More from the Free Merriam-Webster Dictionary." Dictionary and Thesaurus - Merriam-Webster Online. http://www.merriam-webster.com/dictionary/abstracting?show=0&t=1343046707 (accessed July 23, 2012).\\

<sup>4</sup>"Quote Details: Lao-tzu: A journey of a... - The Quotations Page." Quotes and Famous Sayings - The Quotations Page. http://www.quotationspage.com/quote/24004.html (accessed July 23, 2012). 

===== ~ =====
Copyright ©2012 Mithat Konar