the ISO 9001 and ISO 9126 standards covering software quality – (Manjunath M)

The most challenging goal of software engineering is to find better techniques and methods for developing quality and error – resistant software at reasonable cost. In today’s world of information, computers have been applied in to a number of large and critical areas of the industry

Quality characteristics of the software can be measured with a set of attributes defined for each characteristic. These characteristics help evaluating the quality of software, but they do not define a guidance of constructing high quality software products. Quality characteristics are defined in the standard ISO/IEC 9126.

Quality management system requirements are defined in the ISO 9001 standard. The main goal of these requirements is to satisfy the customer needs, which is the measure of quality software product.

In the context of Software engineering software quality refers to two related but distinct notions that exist wherever quality is defined in a business context.

Software functional quality reflects how well it complies with or conforms to a given design, based on functional requirements or specifications. That attribute can also be described as the fitness for purpose of a piece of software or how it compares to competitors in the marketplace as a worthwhile product.

Software structural quality refers to how it meets non-functional requirements that support the delivery of the functional requirements, such as robustness or maintainability, the degree to which the software was produced correctly.

Structural quality is evaluated through the analysis of the software inner structure, its source code, in effect how its architecture adheres to sound principles of software architecture. In contrast, functional quality is typically enforced and measured through software testing.

The structure, classification and terminology of attributes and metrics applicable to softwrae quality management have been derived or extracted from the ISO 9126-3 and the subsequent ISO 25000:2005 quality model, also known as Square. Based on these models, the Consortium for IT Software Quality (CISQ ) has defined 5 major desirable structural characteristics needed for a piece of software to provide business value  Reliability, Efficiency, Security, Maintainability and (adequate) Size.

Software quality measurement quantifies to what extent a software or system rates along each of these five dimensions. An aggregated measure of software quality can be computed through a qualitative or a quantitative scoring scheme or a mix of both and then a weighting system reflecting the priorities. This view of software quality being positioned on a linear continuum is supplemented by the analysis of “critical programming errors” that under specific circumstances can lead to catastrophic outages or performance degradations that make a given system unsuitable for use regardless of rating based on aggregated measurements.


ISO is the International Organization for Standardization that has membership from countries all around the world. It has developed about 19000 International Standards and about 1000 new standards every year.

ISO standards published in recent years are in fields of information and societal security, climate change, energy efficiency and renewable resources, sustainable building design and operation, water services, nanotechnologies, intelligent transport systems, food safety management, and health informatics.


ISO/IEC 9126 ISO/IEC 9126 is one of the best software quality standards in the world. It is intended to specify the required software product quality for software development and software evaluation.

This standard is divided into four parts:

• Quality model

• External metrics

• Internal metrics

• Quality in use metrics

This quality model can be applied in many sectors. It describes the quality model framework that explains the relationships between the different approaches to quality and it consists of six characteristics them is divided into a set of sub-characteristics:

Functionality – a set of software attributes with specific properties that provide functions that satisfy the needs of the user

 Reliability – A set of software attributes with ability to maintain its specific level of performance under the specific stated conditions for a stated period of time.

 Usability – A set of software attributes that are measure of the effort needed user to learn to use the product.

Efficiency – A set of software attributes that represents the ability of the software product to provide relationship between level of performance of the software and the amount of recourses that are used under the stated conditions.

Maintainability – A set of software attributes that are  needed to avoid unexpected effects from specified modifications. This characteristic describes the ease with which the software product can be changed.

Portability – A set of software attributes that are needed for software to be transferred from one environment to another. This is important when the application is made for using on different distributed platforms.

Internal Metrics are metrics that are static and that do not rely on software execution and describe the internal metrics used to measure the characteristics and sub-characteristics identified in quality model.

External metrics rely on running software and they describe the external metrics used to measure the characteristics and sub characteristics identified in quality model.

Quality in use metrics can be measured only when the final product is used in real environment with real conditions and it identifies the metrics used to measure the effects of the quality Characteristics.

Figure 1: ISO/IEC 9126-1 external and internal quality attributes.

In the past years ISO 9000 has proven to be very important and effective tool that cannot be overlooked. According to a study done in Sweden which was focused on factors for implementing the standard, benefits gained after implementation and motives for implementing it, it was determined that the essential interests for getting certification is to increase corporate reputation and quality.

Idea for certification.

ISO 9001 has a goal to implement a group of requirements that when definitely implemented, should supply the costumer and the retailer with confirmation that the goods and services supplied:

• Meet the needs and expectations

• Comply with applicable regulations


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