Skip to main content

The big three: Flexibility Extensibility Maintainability

[Time: 1 min 45 secs]

As we have said earlier, software is rarely ever made and forgotten. After the release, there will be change requests, there will be requests for new features, and bugs to be fixed. And why after the release, even when we are in the process of making software we have to interact with code that has already been written. It is with the goal of easing all of these, that we design software.

The design should enable flexibility, extensibility, and maintainability.

[Time: 9 mins]


  • What is flexibility?
  • Actions for change
    • Identify, Change, Test
  • Detractors of flexibility
    • Complex code
    • Lack of clear responsibilities for classes and methods
    • Unreadable code
    • Repetitions in code
    • Uncontained functionality
  • Design decisions that promote flexibility
    • DRY (Don't repeat yourself)
    • KISS (Keep it simple)
    • No tricks
    • Loose coupling
    • Encapsulation
    • Note: Minimize testing

[Time: 6 mins 25 secs]


  • What is extensibility
  • Actions for extensions
    • Actions for change, adding classes
  • Detractors of extensibility
    • Same as detractors for flexibility (ideally we want to extend the software by adding new classes and not modifying existing classes)
  • Design decisions that promote extensibility
    • Loose coupling
    • Assigning proper responsibilities
    • Proper use of inheritance and polymorphism
    • Design patterns


  • Maintainability is flexibility + extensibility + bug fixes + refactorings

  • All design idioms for flexibility & extensibility apply to maintaibility also. Besides these design factors, some process factors like having proper test cases, and good documentation also apply. But since we are focussing on design in this section, we will not take any process related issues.
  • Remember "maintainability" is the ultimate goal of software design

Note: This post was originally posted on my blog at


Popular posts from this blog

Planning a User Guide - Part 3/5 - Co-ordinate the Team

Photo by  Helloquence  on  Unsplash This is the third post in a series of five posts on how to plan a user guide. In the first post , I wrote about how to conduct an audience analysis and the second post discussed how to define the overall scope of the manual. Once the overall scope of the user guide is defined, the next step is to coordinate the team that will work on creating the manual. A typical team will consist of the following roles. Many of these roles will be fulfilled by freelancers since they are one-off or intermittent work engagements. At the end of the article, I have provided a list of websites where you can find good freelancers. Creative Artist You'll need to work with a creative artist to design the cover page and any other images for the user guide. Most small to mid-sized companies don't have a dedicated creative artist on their rolls. But that's not a problem. There are several freelancing websites where you can work with great creative ar

Inheritance vs. composition depending on how much is same and how much differs

I am reading the excellent Django book right now. In the 4th chapter on Django templates , there is an example of includes and inheritance in Django templates. Without going into details about Django templates, the include is very similar to composition where we can include the text of another template for evaluation. Inheritance in Django templates works in a way similar to object inheritance. Django templates can specify certain blocks which can be redefined in subtemplates. The subtemplates use the rest of the parent template as is. Now we have all learned that inheritance is used when we have a is-a relationship between classes, and composition is used when we have a contains-a relationship. This is absolutely right, but while reading about Django templates, I just realized another pattern in these relationships. This is really simple and perhaps many of you may have already have had this insight... We use inheritance when we want to allow reuse of the bulk of one object in other

Running your own one person company

Recently there was a post on PuneTech on mom's re-entering the IT work force after a break. Two of the biggest concerns mentioned were : Coping with vast advances (changes) in the IT landscape Balancing work and family responsibilities Since I have been running a one person company for a good amount of time, I suggested that as an option. In this post I will discuss various aspects of running a one person company. Advantages: You have full control of your time. You can choose to spend as much or as little time as you would like. There is also a good chance that you will be able to decide when you want to spend that time. You get to work on something that you enjoy doing. Tremendous work satisfaction. You have the option of working from home. Disadvantages: It can take a little while for the work to get set, so you may not be able to see revenues for some time. It takes a huge amount of discipline to work without a boss, and without deadlines. You will not get the benefits (insuranc