Quality in use: incorporating human factors into the software engineering lifecycle

The relationship between the different approaches to quality in ISO standards is reviewed, contrasting the manufacturing approach to quality in ISO 9000 (quality is conformance to requirements) with the product orientation of ISO 8402 (quality is the presence of specified features) and the goal orientation of quality in use in ISO 14598-1 (quality is meeting user needs). It is shown how ISO 9241-11 enables quality in use to be measured, and ISO 13407 defines the activities necessary in the development lifecycle for achieving quality in use. APPROACHES TO QUALITY Although the term quality seems self-explanatory in everyday usage, in practice there are many different views of what it means and how it should be achieved as part of a software production process. ISO DEFINITIONS OF QUALITY ISO 9000 is concerned with quality assurance to provide confidence that a product will satisfy given requirements. Interpreted literally, this puts quality in the hands of the person producing the requirements specification a product may be deemed to have quality even if the requirements specification is inappropriate. This is one of the interpretations of quality reviewed by Garvin (1984). He describes it as Manufacturing quality: a product which conforms to specified requirements. A different emphasis is given in ISO 8402 which defines quality as the totality of characteristics of an entity that bear on its ability to satisfy stated and implied needs. This is an example of what Garvin calls Product quality: an inherent characteristic of the product determined by the presence or absence of measurable product attributes. Many organisations would like to be able to identify those attributes which can be designed into a product or evaluated to ensure quality. ISO 9126 (1992) takes this approach, and categorises the attributes of software quality as: functionality, efficiency, usability, reliability, maintainability and portability. To the extent that user needs are well-defined and common to the intended users this implies that quality is an inherent attribute of the product. However, if different groups of users have different needs, then they may require different characteristics for a product to have quality for their purposes. Assessment of quality thus becomes dependent on the perception of the user. USER PERCEIVED QUALITY AND QUALITY IN USE Garvin defines User perceived quality as the combination of product attributes which provide the greatest satisfaction to a specified user. Most approaches to quality do not deal explicitly with userperceived quality. User-perceived quality is regarded as an intrinsically inaccurate judgement of product quality. For instance Garvin, 1984, observes that "Perceptions of quality can be as subjective as assessments of aesthetics". However, there is a more fundamental reason for being concerned with user-perceived quality. Products can only have quality in relation to their intended purpose. For instance, the quality attributes required of an office carpet may be very different from those required of a bedroom carpet. For conventional products this is assumed to be selfevident. For general-purpose products it creates a problem. A text editor could be used by programmers for producing code, or by secretaries for producing letters. Some of the quality attributes required will be the same, but others will be different. Even for a word processor, the functionality, usability and efficiency attributes required by a trained user may be very different from those required by an occasional user. Reconciling work on usability with traditional approaches to software quality has led to another broader and potentially important view of quality which has been outside the scope of most existing quality systems. This embraces userperceived quality by relating quality to the needs of the user of an interactive product. ISO 14598-1 defines External quality as the extent to which a product satisfies stated and implied needs when used under specified conditions. This moves the focus of quality from the product in isolation to the satisfaction of the needs of particular users in particular situations. The purpose of a product is to help users achieve particular goals, which leads to the definition of Quality in use in ISO DIS 14598-1 as the effectiveness, efficiency and satisfaction with which specified users can achieve specified goals in specified environments. A product meets the requirements of the user if it is effective (accurate and complete), efficient in use of time and resources, and satisfying, regardless of the specific attributes it possesses. Specifying requirements in terms of performance has many benefits. This is recognised in the rules for drafting ISO standards (ISO, 1992) which suggest that to provide design flexibility, standards should specify the performance required of a product rather than the technical attributes needed to achieve the performance. Quality in use is a means of applying this principle to the performance which a product enables a human to achieve. An example is the ISO standard for VDT display screens (ISO 9241-3). The purpose of the standard is to ensure that the screen has the technical attributes required to achieve quality in use. The current version of the standard is specified in terms of the technical attributes of a traditional CRT. It is intended to extend the standard to permit alternative new technology screens to conform if it can be demonstrated that users are as effective, efficient and satisfied with the new screen as with an existing screen which meets the technical specifications. SOFTWARE QUALITY IN USE: ISO 14598-1 The purpose of designing an interactive system is to meet the needs of users: to provide quality in use (see Figure 1, from ISO/IEC 14598-1). The internal software attributes will determine the quality of a software product in use in a particular context. Software quality attributes are the cause, quality in use the effect. Quality in use is (or at least should be) the objective, software product quality is the means of achieving it. system behaviour external quality requirements External quality internal quality requirements Internal quality software attributes Specification Design and development Needs Quality in use Operation