Introduction to Software Engineering

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Introduction to Software Engineering

• CS-300 Fall 2005
• Supreeth Venkataraman

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Introduction to Software Engineering

• The art of building things is nothing new.
• Humans realized the practical aspect of building
  and designing things very early in the history of
  the world.
• The structured approach of building things got
  refined through the ages, and in the modern era
  was given the term Engineering.

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Engineering

• The textbook defines engineering as the art or
  science of making practical application of the
  knowledge of pure sciences
• http//www.engr.washington.edu/score/engineers.htm
  l defines engineering as Engineering is the
  science and art of applying scientific and
  mathematical principles, experience, judgment,
  and common sense to design things that benefit
  society.

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Engineering (Continued)

• There are many disciplines of engineering
  traditionally
• Civil engineering
• Mechanical engineering
• Electrical engineering etc.
• What do all these have in common?
• What about management?

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Software? What on earth is that?

• Lets talk about this for a while.
• How would you define software?
• ?????

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Software (continued)

• Software is a term that is used to refer to a
  computer program or a set of computer programs
  that work towards the solution of problems of
  different nature on a computer.
• Software development is the process of
  transforming a problem statement into a form that
  can be executed on a computer for solving the
  problem.
• So what makes software unique?

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The uniqueness of software

• Can you imagine the world without software today?
• Software is present everywhere. Cell phones,
  automobiles, space shuttles, X-ray machines...
• Software is used both as an end product and also
  in the development of other products.
• Software provides us with all the information we
  need through the medium of the Internet.

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What makes software different?

• For starters, software cannot be touched or felt
  unlike other engineering products.
• Software can have an extremely high complexity
  that makes it difficult to comprehend and leaves
  an extremely large space for human errors.
• Software development is a nightmare if not
  approached in the proper way.

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What is software engineering?

• Consider this scenario. John Doe is given a
  problem to solve on the computer. John sits at
  his computer in his garage, and spews out a few
  hundred lines of code, and gets the required
  output somehow. (Haven't we all done this? ? )
• My question is, Is software engineering the same
  as computer programming?

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Software Engineering (continued)

• Writing a program on a computer is not software
  engineering.
• Computer programming is but one aspect of
  software engineering. It is the implementation of
  a possible solution to the problem at hand, and
  not the solution itself.

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Finally...

• Software engineering is a structured approach for
  developing software.
• Software engineering uses the orderliness and
  discipline of traditional engineering to craft a
  solution to a given problem.
• This process is called the software development
  lifecycle.

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Software Systems

• Software engineering is used to build software
  systems
• A software system is a set of components that
  interact with each other to produce the solution
  for which the software system was developed. Each
  component is usually termed a module.
• Modules communicate with each other using
  interfaces. (Think of one function calling
  another)

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The structured process

• If we were to attempt to solve a problem, how
  would we go about it in a structured way?
• We need to know what the problem is
• We need to determine how to solve the problem
• We need to implement a possible solution
• We need to verify that the solution implemented
  is correct.

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The structured process of software development

• The task of software development is divided into
  well-defined tasks called phases.
• Each phase ends in a milestone.
• The phases of software development put together
  form the process, also called the software
  development lifecycle.
• We will study each component of the lifecycle in
  detail in this course.

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The phases in software development

• Phase I Information exchange between
  developer and end user.
• Phase II Complete problem description
  (developer only)
• Phase III Break down into detailed
  assignments for programming.
• Phase IV Programming
• Phase V Testing
• Phase VI Changing the program

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Information exchange between developer and end
user.

• This phase involves discussions between the end
  user (customer) and the developers.
• The customers tell the developers what features
  they want.
• This is the most important phase of development.
  (Why?)
• This phase culminates in a document called the
  requirements document.

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Complete Problem Description (Developer Only)

• The requirements document is now expressed in a
  form that is understandable and familiar to
  developers.
• The corresponding product is called the
  specifications.
• Specifications state exactly what the software is
  supposed to do from the perspective of the
  developers, and not how the functionality will be
  achieved.
• Requirements state EXACTLY the same, except that
  they are stated in terms that the customer can
  understand.

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Break down into detailed assignments for
programming

• Based on the specifications, the system is broken
  down into components, and each component is
  described.
• Every component has an interface to the other
  components
• The goal is to be able to give well defined
  programming assignments to individual developers.
  
• The milestone of this phase is called the design
  document.

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Programming

• Do I need to say what it is? ?
• This phase transforms the design document into
  working code.
• Ideally this phase should be all mechanical work.
  
• The milestone of this phase is an executable
  program that can run on computers.

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Testing

• Testing is the process of checking whether the
  software is doing what it is supposed to do.
• Does the software correspond to the requirements
  completely?
• This involves trying out different input values
  on the program and examining the output to check
  if the expected output is obtained.
• The milestone of the testing phase is the tested
  software.

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Changing the program

• What happens when the software is deployed?
• Usually, the customers start finding
  inconsistencies in the software (Hey, this is not
  what I asked for!)
• The software has to be patched in order to get
  it working as needed
• When the program is changed, it means that it has
  to be tested again.
• And so life goes on

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Words of Wisdom

• Thanks to Charlotte Mahoney for this slide
• Writing software is an art, as well as a science.
• Software engineering researchers
• Design computer systems and write programs to
  perform tasks on those systems, which requires a
  great deal of art, ingenuity, and skill.
• A software engineer is responsible for solving a
  given problem through careful design and
  analysis, before beginning to implement the
  solution.

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Conclusion

• Software engineering uses a structured process
  for software development
• Like any other form of development, resource
  management (people, equipment, money) is
  essential for software development
• Management issues are as important as development
  issues.

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Study Questions

• Why is software engineering different from other
  types of engineering?
• What is the difference between software
  engineering and computer programming?
• What are the products of each phase in the
  software development lifecycle?
• Give me a name for each of the phases in the
  lifecycle.