introduction to software engineering

What is Software Engineering?

  • In Software Engineering we study how to build and maintain software systems in a controlled, predictable way.
  • In particular, good Software Engineering should give control over:
    • Functionality
    • Quality
    • Resources


  • The system should provide functions that meet the needs of all the stakeholders of the system.
  • This will involve determining what these needs are, identifying and resolving conflicting needs, and designing a system that meets the identified needs.


  • The quality of a system determines if it is useable in its intended context.
  • The required quality of software varies enormously.
  • Software on a desktop PC is usually of fairly low quality while the control software for railway signalling applications needs to be of the highest standard.
  • The required quality strongly determines the cost of software production.


  • The purchasers of a system usually enter into a contractual relationship with the supplier companies.
  • The suppliers need to predict resource requirements:
    • Quality of development team
    • Human effort
    • Timescales
    • Supporting tools and equipment
  • Failure to predict costs can have serious consequences for the suppliers and purchasers of systems.

Software Evolution

  • The process of developing a software product using software engineering principles and methods is referred to as software evolution.
  • This includes the initial development of software and its maintenance and updates, till desired software product is developed, which satisfies the expected requirements.
  • Evolution starts from the requirement gathering process.
  • After which developers create a prototype of the intended software and show it to the users to get their feedback at the early stage of software product development.
  • The users suggest changes, on which several consecutive updates and maintenance keep on changing too.
  • This process changes to the original software, till the desired software is accomplished.

Software Evolution Laws

  • Lehman has given laws for software evolution. He divided the software into three different categories:
    • S-type (static-type)
    • P-type (practical-type)
    • E-type (embedded-type)

S-type (static-type)

  • This is a software, which works strictly according to defined specifications and solutions.
  • The solution and the method to achieve it, both are immediately understood before coding.
  • The s-type software is least subjected to changes hence this is the simplest of all.
  • For example, calculator program for mathematical computation.

P-type (practical-type)

  • This is a software with a collection of procedures.
  • This is defined by exactly what procedures can do.
  • In this software, the specifications can be described but the solution is not obvious instantly. For example, gaming software.

E-type (embedded-type)

  • This software works closely as the requirement of real-world environment.
  • This software has a high degree of evolution as there are various changes in laws, taxes etc. in the real world situations.
  • For example, Online trading software.

E-Type software evolution

  • Lehman has given eight laws for E-Type software evolution:
    • Continuing change – An E-type software system must continue to adapt to the real world changes, else it becomes progressively less useful.
    • Increasing complexity – As an E-type software system evolves, its complexity tends to increase unless work is done to maintain or reduce it.
    • Conservation of familiarity –The familiarity with the software or the knowledge about how it was developed, why was it developed in that particular manner etc. must be retained at any cost, to implement the changes in the system.
    • Continuing growth- In order for an E-type system intended to resolve some business problem, its size of implementing the changes grows according to the lifestyle changes of the business.
    • Reducing quality – An E-type software system declines in quality unless rigorously maintained and adapted to a changing operational environment.
    • Feedback systems- The E-type software systems constitute multi-loop, multi-level feedback systems and must be treated as such to be successfully modified or improved.
    • Self-regulation – E-type system evolution processes are self-regulating with the distribution of product and process measures close to normal.
    • Organizational stability – The average effective global activity rate in an evolving E-type system is invariant over the lifetime of the product.

Software Paradigms

  • Software paradigms refer to the methods and steps, which are taken while designing the software.
  • There are many methods proposed and are in work today, but we need to see where in the software engineering these paradigms stand.
  • These can be combined into various categories, though each of them is contained in one another:

Software Development Paradigm

  • This Paradigm is known as software engineering paradigms where all the engineering concepts pertaining to the development of software are applied.
  • It includes various researches and requirement gathering which helps the software product to build. It consists of –
    • Requirement gathering
    • Software design
    • Programming

Software Design Paradigm

  • This paradigm is a part of Software Development and includes –
    • Design
    • Maintenance
    • Programming

Programming Paradigm

  • This paradigm is related closely to programming aspect of software development. This includes –
    • Coding
    • Testing
    • Integration

Need of Software Engineering

  • The need of software engineering arises because of higher rate of change in user requirements and environment on which the software is working.
    • Large software – It is easier to build a wall than to a house or building, likewise, as the size of software become large engineering has to step to give it a scientific process.
    • Scalability- If the software process were not based on scientific and engineering concepts, it would be easier to re-create new software than to scale an existing one.
    • Cost- As hardware industry has shown its skills and huge manufacturing has lower down he price of computer and electronic hardware. But the cost of software remains high if proper process is not adapted.
    • Dynamic Nature- The always growing and adapting nature of software hugely depends upon the environment in which user works. If the nature of software is always changing, new enhancements need to be done in the existing one. This is where software engineering plays a good role.
    • Quality Management- Better process of software development provides better and quality software product.

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