Software Quality Charateristics in ISO 9126

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 Characteristics

The main software characteristics in accordance to ISO 9126 are:softwarequality-en

  1. Functionality
  2. Reliability
  3. Efficiency
  4. Usability
  5. Maintainability
  6. Portabilty

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:

  1. Suitability
  2. Accuracy
  3. Interoperability
  4. Security
  5. 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:

  1. Maturiy
  2. Fault Tolerance
  3. Recoverability
  4. 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.


Sub-characteristics are:

  1. Time Behavior
  2. Resource Utilization
  3. 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:

  1. Understandability
  2. Learnability
  3. Operability
  4. Attractiveness
  5. 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:

  1. Analyzability
  2. Changeability
  3. Stability
  4. Testability
  5. 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:

  1. Adaptability
  2. Installability
  3. Co-Existence
  4. Replaceability
  5. 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.

Sum Up

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.

5S Methodology and Software Development

The 5s methodology is used to keep the working environment clean, ordered and efficient. I came across this methodology when I was working in a production area for a semiconductor factory. This system was referenced from time to time when internal audits showed some weaknesses in regard to efficiency, order or cleanness. For a short reference on 5s methodology have a look to:

The key topics Sorting, Straightening, Shine, Standardize, and Sustain are quite weak translations of the Japanese words Seiri, Seiton, Seiso, Seiketsu, and Shitsuke due to the wish to translate it into English words which also start with the S letter. Nevertheless, they express roughly the idea behind that and details are explained below. Again like for the post about the Seven Muda, I also translate these topics into the field of Software Engineering as I understand it.

Sorting (Seiri)

This principle has a strong relation to the Muda Inventory, Over-Processing and Over-Production.

Classic meaning:

The meaning here is: Remove everything unnecessary. Check all tools, materials, and machinery and remove everything which is not needed. This cleans out the workspace, makes spaces and removes distraction. The rate of defects decreases due to a lowered risk to use wrong tools or materials and more space means less incidents.

Software Engineering:

For software engineering it is the same, but it is twofold:

  1. For development process: Remove all tools and stuff in your workspace, IDE or PC which is not needed. These tools distract the developer, make the workspace cleaner as mentioned above and also sometimes more stable (everyone who uses Eclipse with a lot of plugins know, what I mean).
  2. For Architecture and Design: Remove all components, interfaces, libraries, and systems which are not needed. These are added as soon as they are needed. For example: To implement everything in patterns right from the beginning does not make much sense, when  not needed, yet. The requirements may change and what was though at the beginning is needed, will not be needed further on. Only use and implement, what is needed and postpone everything else into the future when needed.

Not hitting the correct meaning, but also part of it is duplicate code. Duplicate code is something which is redundant. Redundancy is also something which needs to be cleaned out. Duplicate code is a nightmare for maintainability and should be avoided in all means.

Straightening (Seiton)

This principle has a relationship to Muda Transport, Motion and Waiting.

Classic meaning:

This principle is about straightening the processes. Everything should be processed in an efficient way. Transport ways need to be shortened, motions to be avoided, unnecessary tasks to be eliminated and wait time to be reduced. This principle can only be applied in iterations with close observations.

Software Engineering:

In software engineering this principle can be used as a driving factor for lean architecture and design. The Muda Transport, Motion and Waiting in post about the Seven Muda give hints were to look out in software engineering.

Shine (Seiso)

Classic meaning:

This is about cleaning and ordering the workspace. As soon as everything is clean and ordered, the station is ready for usage. In each shift or on daily basis, cleaning and ordering should be scheduled. On such a workspace, process flaws and defects are better to find and the work is easier, cleaner and safer.

Software Engineering:

For software engineering, I would refer to Clean Code and Refactoring. Write clean code and clean the code as soon as bad smells are detected. This keeps the code clean and erosion is prevented. Bugs are easier to spot in clean code and also easier fixed.

With refactoring the architecture and design stays clean, too. This assures an understandable architecture which support bug fixing and improvements.

These actions should take place during normal work, but also scheduled at the end of sprints for instance. Code Reviews can also set in place in critical parts of the software to assure the right measure of quality. A time budget from 5% to 50% depending of the state of the code should be scheduled. In brown field projects with a lot of legacy code massive cleanup can help to improve the later development of new functionality dramatically. But, also in green field projects erosion takes place and should be fought with a 5% time budget at least. Have a look to the books Refactoring by Martin Fowler and Clean Code by Robert C. Martin for details, or Working Effectively with Legacy Code by Robert C. Martin.

Standardize (Seiketsu)

Classic meaning:

In fabrications all work stations should be standardized, what means that they should look, function and feel all the same. It is more easy to train people on a new station that way, the quality is higher due to a lower defect rate and it is also cheaper if it is possible to reuse procedures, tools and material.

Software Engineering:

For software engineering, there are two possible meanings:

  1. All developers should use the same tools for development. It is more easy then to maintain a development environment where only one IDE is present, one build system, on OS and so forth. Only for testing there may be some variation, but for pure development, it is easier to deal with one kind of tool for one purpose.
  2. Within the software everything should be handled in a standardized way. So the architecture should define standards and also design. For instance it could be a standard that all components of a larger system communicate to each other with a REST interface. There only one REST library is used. It would be worse if all components would talk with another protocol like SOAP, RMI, EJB and so forth. For design it is the same. Exception handling for instance should be defined how it should be done. How are files handled? Coding guide lines and so forth.

Standards help that people can identify parts in larger systems more easily. Understandability and Maintainability improve dramatically.

Sustain (Shitsuke)

The first four points are hard enough to accomplish, but this sustaining point is even harder. What you did and accomplish in the first four sections is a large step to an efficient production environment. This is something which is done in form of a project, but a project is time limited. The real art of 5S is now to keep the state what was accomplished and to even improve it. That’s a huge leap! The goal is to establish a control system which checks for instance from time to time the current situation in a kind of internal audit and to raise the issues found. The issues should be fixed as soon as possible. With a regular check of the other 4S and an improvement of the findings, the current state can be sustained and even improved. But, this needs a lot of attention and energy.

In Software Engineering the buzz words Code Smell (or just Smell), Refactoring and Architecture Refactoring come to mind. As soon as there are bad smells, an action needs to be taken to fix this issue. The longer the issues is present, the more it manifests itself and the harder is it to be fixed. As the Asian proverb says: It is easy to change the direction of a river at its source…

Further Enhancements

Sometimes some enhancements are added. These points express some enhancements which should be taken care of, too. I only explain them shortly, because they are quite self explanatory.

Enhancement to 6S: ‘Get Used to it’ (Shukan)

This point is often added to the original 5S. With the checks and fixes in the Sustaining part, people get trained to keep an open eye on 5S. Over time everybody should develop a habit of fixing everything which is not in order to have an easier and more efficient life. It is good to create a company culture for 5S.


Classic meaning:

This is very easy: Keep everything and order and additionally, watch out for sources of accidents and prepare everything that this accidents cannot happen.

Software Engineering:

Here it is about the quality of source code and architecture for accidents like crashes, wrong results, stability and so forth.


Classic meaning:

Keep people out which are not supposed to be in certain area. Keep secrets secret and confidential data confidential.

Software Engineering:

Build  your software in a way that only authenticated people are allowed to change settings which they are authorized to and keep data protected from people which are not allowed to see them.

The Seven Muda (Wastes) and Software Engineering

I was introduced into the term Muda (waste) when I was working for a semiconductor fab. I learned that there a seven of them and that  a close look out to these wastes can reduce costs and increase quality dramatically. A short introduction about it can be found here:

I want to write about these wastes with a shifted focus. The seven Muda were formulated for classical production and ‘real world’, but as we can see later on, these principles can be used for software engineering, too. Looking out for these wastes can help to make architecture, design and code lean and clean.


Classic meaning:

The classic meaning is the reduction of transportation. This means, one should look out for everything what is transported and how these transports can be minimized. In fabrication it means for example that the transport for goods can be optimized by ordering larger quantities, to use vendors which are closer by and so forth. The transportation costs can be reduced and the margin can be increased. Transportation does not add value to the product, but it adds risk. During any transport operation the risk is there for breaking, loosing and delaying the product.

Software engineering:

Transportation can be translated here for example to IO. Avoid transportation over network, to disc and what so ever. If IO can be reduced, the timing is better, bandwidth is saved and other applications and systems are not affected negatively by a bandwidth exhaustion due to excessive use of IO of one system. To safe IO, good data models should be used for a high reuse of data. Double fetches could be avoided, only data which is needed is fetched from a DB for example and not the whole database is read just in case… Savings here leads directly into more responsive systems, reduced costs for IO facilities and high throughput.


Classic meaning:

The meaning of Waste of Inventory is quite easy. It is about the waste to have raw material, finished products and work in progress laying around without the prospect to monetize it. It may or may not be sold. In this state it is a potential waste and should be avoided. A waste of inventory may lead into selling the products under value or even into dumping them.

Software engineering:

In software engineering inventory is twofold:

  1. Source Code: Writing source code which is not requested by the customer (directly or indirectly) may not lead to revenue. So it is a waste of time and also resources to produce it. Only functionality which brings in revenue is to be developed. Everything else is potential waste, like finished products laying in a warehouse without a demand by customers. A lot of money can be saved by letting developers produce software which adds value and brings in money. Also trial and error development (or Programming by Coincidence like described in The Pragmatic Programmer by Andrew Hunt et. al.) is waste. All development versions which are dumped on the way to the final version are waste. Some thoughts in advance can save a lot of time, money and trouble.
  2. Data: With the ‘Big Data’ discussion the Waste of Inventory is put into public again. Every piece of data stored costs some money. Even one pays storage by cents per gigabyte, the big amount of data makes it expensive. Data should be stored only if needed and selected carefully. Costs for storage can be reduced. Due to date is transported to the storage facilities, transport costs are also reduced.


Classic meaning:

When transport is about bringing the goods from one facility to another or from one machine to another, than Motion is about the handling of products during the production process. The more handling is involved during production, the more time is needed for that action and risk is added for damage and low quality. Also, motion is mechanical motion and lead into a degeneration of the machines used. For people it is the same. To much handling of products lead to illnesses and other issues which also cost money in form of sick days. Avoiding motion reduces costs for maintenance, sick days and broken products.

Software engineering:

Motion is software engineering is not so easy to define. The closes equivalents in my opinion are:

  1. Motion = unnecessary things done in software. This may be an animation too much which is not needed, but might break the application by its presence and wastes CPU time. It may be a storage operations too much just to be save some data temporarily for a case of power failure, but it the data could be recalculated if needed. There might be a watchdog to much. Defensive programming is find, but too much is not needed. Things done unnecessarily lead into waste of time and resources. The software runs longer and wastes CPU time. Sorry, I do not have a better explanation, but maybe you get the point.
  2. Motion = unnecessary things done during software development process. This can mean unnecessary work due to Programming by Coincidence due to missing design sessions. It can also mean writing unnecessary documentation, design papers and such stuff. It can mean unnecessary meetings, conference calls and status presentations.


Classic meaning:

Every product in Work which waits for something, does not add value, consumes space and the delays may lead to a bad reputation. All wait times need to be reduced. This can be done by queue managing. Have a look to the book The Principles of Product Development Flow: Second Generation Lean Product Development by Donald G. Reinertsen for more information.

Software engineering:

In software engineering, the most obvious waste due to waiting would be a programmed delay or sleep in a program to wait for something. This is obviously not a good design. Better do a design with asynchronous execution and notification. A program should always do something meaningful if possible. Do not wait for something to happen. Do something in meanwhile and wait for notification for example or have some processes in parallel which fill up the CPU time of a sleeping thread. All waits are a waste of customers time. This should be avoided, otherwise it leads into frustration without adding value to anything.


Classic meaning:

In classic fabrication this means: You do something better, more accurate or more beautiful than required. The customer is paying for a product with a negotiated specification. This specification needs to be met, but not more. More work on the product will lead into higher production costs, more time needed and more risk for damage without a monetary compensation.

Pay attention: Over processing can be a part of a marketing strategy and a customer satisfaction program. By over delivering a customer may be surprised positively which may lead to a returning customer, a higher order for the next time and so forth. This is not over processing as it is meant above. This is part of a strategy which brings higher revenue in future.

Software engineering:

Over processing is quite the same as in classic engineering. A software product calculates more accurately than needed. The performance tuning was done extensively to get the last microseconds out of the calculations. And there are much more things like that. As long as the product is good enough, we should stop working on features already done. It does not bring more value to the customer.

Here too: Please pay attention for over delivering. This is a magic tool if done right. See above at the classic engineering section.


Classic meaning:

Over-production is simply the production of more pieces of a product than needed the time of production. There is a risk that not all products which were produced can be sold. The avoidance of over production reduces costs, reduces the amount of resources needed for production and is also good for the environment.

Software engineering:

Over-production has two meanings in software engineering, as far as I can see it:

  1. Over production of results: A software product which produces more results than needed, wastes resources and time. This is not what customers want and that is also nothing they want to pay for. At least, provide configuration possibilities.
  2. Over production of features: In software engineering (as in all engineering disciplines), engineers tend to over-engineering. Full blood engineers want to make the product perfect, feature rich, shiny and so forth. This might lead to feature bloat. Every feature which is not requested by the customer does not add value. A customer will not pay more money for functions they do not want to use. That’s why a lot of products come in different flavors like community, basic and enterprise version. The customer chooses what features are needed and pays for exactly them.


Classic meaning:

Defect products need repairing or if they can not be repaired, need to be dumped. Both choices cost money. Additionally, the reputation is influenced negatively which costs future money due to customers not wanting to pay again for a product from the same manufacturer. It becomes even worse as soon as the defect damages something on customer site and the customer asks (un-)politely for regress. A good customer support division can compensate a lot, but this is expensive, too. So: Defects should be avoided. They always waste a lot of money.

Software engineering:

For software defects the same facts are valid like for mechanical engineering. Defects cost money and reputation. So, the best is not to have any. Avoiding defects by excessive testing and quality control is cheaper than handling angry customers, doing failure analysis, bug fixing, patch releasing and loosing future customers.

Additionally as 8th Muda: Latent skill

There is an additional unofficial 8th Muda: Latent skill. Officially, it is spoken about utilizing the skills of employers. People which were hired to fill out a certain position might be able to do much more or more valuable work than what the position requires. These people should be given an oportunity to grow and do what they are capable of. Additionally, a lot of employees want to learn more and want to be trained. It is not only about getting a higher salary, but also about personal grow and satisfaction.

In my opinion there is another site of Latent Skill Waste: It is about machinery. Some high-tech machines are capable of doing more, than there were bought to do. They can be utilized if it is possible. In IT this is were cloud computing was invented. It is partly waste by waiting and waste by latent skill, when servers are not utilized due to too less work. With cloud computing utilization of servers can be increased. This utilization comes in two flavors: Doing more of the same work (reducing waste of waiting) or running other services in parallel (reducing waste due to latent skill). A higher utilization means more revenue and therefore more profit, because the deprecation costs are the same.

A Final Thought

The Muda are not meant to be used for cost reduction in first place. The mind set is not correct, in my opinion. The Muda are about efficiency. To do cost reduction, efficiency needs to be increased, that is correct. But, to think about cost reduction only leads into decisions which might hurt quality and effectiveness. About the difference in mind set and practical approach, I might write about later on in another post.

Thoughts on the Agile Manifesto

From time to time, I discuss the agile methodology with clients and friends. The Agile Manifesto was published at about 12 years ago. It was debated a lot and the debates still are going on. I try present here a small inside I had during the last years.

The main statement is

“Manifesto for Agile Software Development

We are uncovering better ways of developing
software by doing it and helping others do it.
Through this work we have come to value:

Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan

That is, while there is value in the items on
the right, we value the items on the left more.

Interestingly, the focus is shifted from the product, its documentation and the technical process (the planning) to customer focus and customer satisfaction. This is also part of another system which is called Total Quality Management ( The focus shift is very obvious and necessary, when we think about the only income source each company has: The customer. The customer (or different customers if an organization has different services to offer) is the only source for income and therefore for revenue, profit and growth. Any revenue increase can only happen, when customers pay more for services or products or more customers are willing to spend money on the companies services or products. It is therefore obvious, that the focus needs to be on the customer and that the organization needs to be aligned to meet the needs and expectations of customers.

That’s why the first point about ‘Individuals and interactions’ is the most important point. Translated to easy actions it means: Identify your customers, treat them individually and implement processes for easy communication and interaction. Only customers can tell you what they need, what they expect and what they are ready to pay for. Individual customers treated well, will tell you more detailed, what they need and bring new business ideas. Ask a group of people and there is no detail. But, ask a single individuals and listen closely. You might get a lot of insights.

In software development the main reason of organizations is delivery working software and systems. These are the primary needs of their customers. They do not need a fancy manual to read, what the software might be able to do after spending hours to read the manual and trying things out in tutorials, but they need a software which brings business value. That’s why the second point is important. Have a running, valuable software which is self-explanatory and the customer is willing to pay for it. You can save a tree by dropping the printed documentation. Have a look to Apple products. How much manuals are sold with this complex and feature rich software? Some only help and a self-explanatory UI and everything is fine. This is one of the fundamentals of Total Quality Management: Only the customer can tell you what she wants and she is also the one who pays. Is there another way to work with the knowledge?

The third point is the enhancement of the first point. If the chance is there, try to work with your customer closely together. In Scrum and XP it is done by short release cycles and demos to show the customer progress on regular basis after each release cycle and ask for critics, comments and new ideas. It helps to deliver software which is valuable for the customer and therefore, which is paid for. An even better idea is to embed a representative of the customer into the development team. The responses are immediate and customer’s acceptance testing is done the whole time. The possibility of developing software for what the customer does not want to pay, is reduced dramatically. And again: The customers pays for the product. There is no way to make a better product than to build the product together with your customer and when the customer is part of the team, she is even more engaged and willing to help for development. At the very end, the willing to pay is much higher, when the product was kind of custom built.

By doing all this, be prepared: With each demo, feedback session and communication to the customer, there might be new ideas, comments and critics. The requirements are about to change on daily basis. That’s what the fourth value is about. Be open for changes. Customer only have vague idea at the beginning, about what they want. But, during the development, more ideas arise, some faulty ideas are dropped and new wishes pop up. That’s kind of normal and part of the process. This helps to make the product better at the end and the business value is increased. A product like that can be priced higher, though. What is better than that?

Is “good enough” good enough?

I thought about the term “good enough” lately. It came into my mind, that the term is used in a kind of way which is misleading.

In a lot of books about quality and economics (books which deal with the combination of the two) it is written, that development should not be perfect, because it is economically not meaningful, but it should be good enough. The hint is right, but misleading. It is not explained in detail what ‘goo enough’ really means, at least not in the books I wrote about that topic.

The term good enough is treated in almost all cases I witnessed as: Good enough = Good enough to be sell-able. This leads to a focus on external design, usability and feature bloat to increase market value. The market value in most cases is only judged by the external attributes. Most buyers do not look into the products and judge the internal value, what in most cases also would not make much sense. That’s why colorful products, well-designed and products with a ton of features can be sold best.

There is nothing wrong about the fact that such products can be sold best and most easy, but from the business point of view, this is not enough. What is good enough for the end customer, is not necessarily good enough for the producer of the product. All products have more needs than just to be sell-able. Products need to be recyclable, maintainable, ecological and maybe also upgradable (and much more). These thoughts lead to the conclusion, that there is more to think about than just the market and to be good enough for the market.

In software industry for instance, the source code of a current product is used as foundation for all further products. As soon as the source base gets unmaintainable, all future products are in danger. Software is very complex to develop and therefore, very expensive. A complete new development of a source base of a product family is very expensive and only large companies can handle and survive that.

It is therefore very important, right from the beginning, to spend some effort on code quality. The application of metrics, defect checks and conventions is crucial. Otherwise, the future of a company can be in danger.

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