Monthly Archives: May 2010

A Software Quality Model (Part I)

This is the first post, of more to come, about my thesis and the software quality model I have developed.

First I will explain in what context my thesis is placed. This post will focus on decisions made to actually form a ‘new’ model (actually, derived from…).

For my thesis I have investigated how to improve quality of a software product. The first step was to choose one of the five perspectives on quality, given by Garvin (see here for more information). The product based perspective is chosen for scoping reasons. With that perspective in mind, three software quality models where evaluated:

The first, and one of the most known models, is the model of Boehm (literally translated ‘the tree of Boehm’):

The second model was from Willmer and the third from Bemelmans. Basically Willmer takes Boehms model and took it a bit further in order to translate customer desires into metrics. Bemelmans takes a whole different approach: He takes three main characteristics: “requirements for usage”, “requirements for maintenance” and “requirements for product information”. Which each have their own sub-characteristcs. (though it does not look like a tree like Boehm, as it only has one dimension).

One model actually caught the attention because it tends to ‘translate’ customer language into a developer language. The basic idea is that a software quality characteristic is mapped with a metric. Unfortunately the book I had did not tell how to translate this. Also, there was a need to translate customer language into software quality characteristics. This was something that was not being explained either.

So how does the translation look like? Imagine a matrix, where at the left several software quality characteristics are given (for every row). And at the top, every column is a metric. With some means you could assign metrics to characteristics and get a basic idea what is important.

Taking the ‘translation matrix’ of Willmer as a starting point, I have developed a model that actually does three things:

1st. It translates customer language into software quality characteristics. Not only that, but it also gives a % of relevance. (more on that later).
2nd. The actual translation from characteristics to metrics. This looks a lot like how Willmer does this, but it also has a % per metric per characteristic.
3rd. The  interpretation of metrics. This is where things get really concrete. Here the actual scoring is defined. How will the metric LOC be interpreted?

With these three, it is possible to actually ‘calculate’ the total quality of a software product, with the ‘product based perspective’ of Garvin in mind! (So, it does not tell you how to improve your processes. Nor does it tell you how customers experience the website).

So how do you use this model? Using the “Plan/Do/Check/Act” (Circle of Deming) as basis, the suggested plan is:

– First ‘define’ quality.  (Plan)
– Meassure and analyse (Do)
– Evaluate (Check)
– Change definition / software (Act)

In my next posts I will explain briefly how the model looks like.

The need for quality of Web Applications

I’ve been working on my thesis (about meassuring Software Quality) and its reaching its final state. I will blog some posts about my thoughts and findings about Software Quality from here. This post was a bit old, I dusted it off and actualised it a bit. More to come!

Here it comes:

Today, it is unthinkable to not use an internet related service in your daily life. Think about staying in touch with family and friends using email (gmail, yahoo, hotmail, etc), social networking (twitter, facebook, hyves, etc) or more.

If you want to book a trip, you arrange this using the internet. When you want to buy a new laptop, you find the specs and reviews on the internet. You use a comparison site to find the cheapest (web)store. And if you want to buy it, you use the internet.

It is fair to say that the internet has become more and more important to our lives. Even more than we imagined 5 years ago. How would we deal when our mail provider is down? How would we react when facebook is down? What about twitter? How do we do our bank business when we cannot reach the online-banking site?

I think you got the point.

Companies developing and maintaining (ecommerce) websites or services are constantly pressured to deliver high quality software in the shortest possible amount of time. Having these factors, time and quality; one cannot exclude the other. They do influence each other though. When you want to deliver fast, you ought to make sacrifices in terms of designing and testing the product. This will eventually lead to a lower quality. The opposite is true as well, if you spend more time in the design and testing, you will likely deliver higher quality. Also, unlike with traditional software, it is not always the first to deliver that is the best.

In the land of the internet, it is not only the case to get users to your website, but also to keep them revisiting. If you deliver a fancy new feature, you might get the attention. But if you did not put enough effort to make it high quality, you might lose them to your competitor who delivers a similiar feature a few days later, but twice as good. Remember, your visitors can easily switch if you cannot deliver what they expect.

So what does a visitor expect from a website? Looking around on the net you can find some definitions of quality of good websites. That is the biggest question of all. How can you deliver fast, and yet have some sort of quality to rely on?

You could use a Software Quality Model for that, like the ISO-9126. I would say, you’d use a model like the ISO-9126 and create/use a Web Application Quality Standard.

So what is this standard? I haven’t found a definite model, although I have found a good resource here.
In my opinion, the following Software Quality Attributes would belong in such a model:
performance. Your visitors will leave if loading a page takes longer than 2 seconds. Directly influencing possible sales!
security. Atleast be aware of the top ten of OWASP. Better yet, make sure you are not vulnerable to these exploits.
maintainability. Developers should be able to easily extend code, or fix bugs without causing too much regression.
reliability. Should your website simply shut down once the load is too high? How much ‘page faults’ may appear? One of thousand requests? One of hundred?.

Each of these attributes can be split into several measurable units. For example, performance wise you could measure the amount of time it takes to get a page loaded in the browser. Maintainability has some known measures (like McCabe’s Cyclomatic Complexity).

Note: Recently I figured that the ISO-9126 is actually not a model, but a ‘standard’. It really does not tell you *how* to do things, but it does give guidelines. The Software Quality model I’ve made does tell  you how to do things.