In ISO 9126 software quality characteristics are defined which are used to evaluate the quality of a software product. These characteristics shall assure a complete evaluation, but in most projects these characteristics need to be weighted to each other. This evaluation procedure is quite complex and it differs from project to project and maybe also over time due to changing requirements (Agility). I want to give here a starting point for the discussion which is true in most projects, but need to be refined.
The main software characteristics in accordance to ISO 9126 are:
A graphical representation of this main characteristics and the sub-characteristics is show nearby. I already ordered them in correspondence to the importance for most software projects. But, this is only half of the truth. In the following sections the explanations are provided.
Security is divided into the following sub-characteristics:
- Functional Compliance
This is the most crucial point for customers. With incorrect results, unsuitable models and software which can not inter-operate with their environments, our software is useless. A software which has not the functionality needed, is never accepted by customers.
The sub-characteristics are:
- Fault Tolerance
- Reliability Compliance
Reliability is the second most important point in software development. As soon as the software has a certain functionality, this functionality needs to be available. This is needed to generate a constant revenue, to provide services to end user for their satisfaction or to monitor safety critical operations. A weak reliability will lead to loss of revenue, loss of customers and in critical area to injuries and deaths.
- Time Behavior
- Resource Utilization
- Efficiency Compliance
Our customers have fabs where they try to increase the throughput on daily basis. Our software needs to be performant, too. We should pay some attention to performance and resource usage. But, this must no be on cost of maintainability. Ask your senior about the right decisions if unsure.
The sub-characteristics are:
- Usability Compliance
Our customers and clients want software which is self-explanatory and easy to use. We should keep in mind to keep our customers happy with nice and usable GUIs, too.
Maintainability’s sub-characteristics are:
- Maintainability Compliance
This is the most important point for ourself! Code which is not maintainable leads to code which can not be changed, can not be kept stable and secure and may lead into a product which can not be sold. On the other side, we can make our lifes much easier with easy to read and easy to write code.
The sub-characteristics for Portability are:
- Portability Compliance
This point is of minor importance, but should be kept in mind by architects. The system itself and technologies used within our products are meant to change in future. We should build systems in a way, that sub-systems may be changed without too much work.
As I wrote before, the statements I made above will be true for most software products, but there are always differences from one project to another. The ordering above will lead into good software which is also sell-able, but it is kind of focused to technical
Let’s have a short look to Video Games: As far as I observe the market, the priorities are different here. Performance in Video and Realism (Efficiency) are one of the highest values and Reliability comes behind. In forums people talk about awesome graphics and realism, but they complain about stability issues within new products, but the products are bought nevertheless. It is the graphics which is valued most. Sometimes the functionality also is behind Efficiency. There are some video games out there with a very thin story, which are not intuitive to use, but which are bought for the cheer graphics and their open world.
Another example is software for end users: Here the Usability is ranked in most cases above Efficiency. End user need to have a good time using the software. Easy usage is much more important for them then waiting for some seconds for an operation to finish. The famous flying object which show activity, nice graphics and so forth are more important than efficiency. Have a look to one of the famous smart phone manufactures: There OS looks great, is easy to use and is stable. The functionality is not overwhelming, but it is stable and fast enough. The priorities are set right, but different then I wrote above.