Sep 10 - Related Standards, 3 Level Conformance, Definitions (CISU-R part 2)

NISTIR 7432

Common Industry Specification for Usability - Requirements

1. Scope

1.1 General

The CISU-R describes how to specify usability requirements for both hardware and software products. It is consistent with the definition of usability in ISO 9241-11: effectiveness, efficiency, and satisfaction in a specified context of use.

Usability requirements based on the CISU-R have three parts:
1 The context of use
2 Peformance and satisfaction criteria
3 The test method and context for testing.

The CISU-R does not prescribe any specific development process. The CISU-R does not prescribe specific measures for usability.The CISU-R does not prescribe any specific user centered design process, but it is consistent with the relevant process in ISO 13407.

1.2 Relationship to other standards

1.2.1. General

The CISU-R can be used in conjunction with other related standards.

1.2.2. Relationship to ISO/IEC 25062 – Common industry format for usability test reports

As a tool to support testing and verification, the requirements specified in the CISU-R can be tested and the results reported using the ISO/IEC 25062 (Common Industry Format (CIF) for usability test reports). Organizations can develop their test and verification plans directly from the CISU-R.

1.2.3. Relationship to ISO 13407 - Human centred design processes for interactive systems

IS0 13407 defines one of the stages of user centered design as the specification of requirements. Usability requirements created using the CISU-R are consistent with the recommendations of ISO 13407.

The CISU-R directly supports the following objectives in ISO 13407:1999 7.3.2:
"The specification of user and organizational requirements should
a) identify the range of relevant users and other personnel in the design,
b) provide a clear statement of the human-centered design goals,
c) set appropriate priorities for the different requirements,
d) provide measurable criteria against which the emerging design can be tested,
g) be adequately documented."

1.2.4. Relationship to ISO/IEC 9126 – Software Engineering – Product Quality

Usability requirements, as defined in the CISU-R, are used in conjunction with other detailed design requirements, such as those in Annex B. The development of these detailed requirements may be supported by the use of standards such as ISO 9241 or ISO/IEC 9126

The CISU-R enables usability to be specified as an outcome of interaction, measured as user performance and satisfaction. ISO/IEC 9126-1 defines this as a high level quality objective: the user’s experience of the "quality in use", which is determined not only by the features of the user interface, but also by the extent to which the functionality supports the user’s tasks and by non-functional requirements such as acceptable computer performance and reliability.
Examples of metrics for usability requirements can be found in ISO/IEC 9126 parts 2 and 3.

1.2.5. Relationship to ISO/IEC 25030 – Quality requirements and guide

Usability requirements in this document correspond to the quality in use requirements in ISO/IEC 25030

2. Conformance

2.1 General

The three levels of compliance also allow conforming requirements to be written at an appropriate level of detail for each product and development process. Each of these levels builds on the previous level(s), allowing requirements to be specified iteratively, adding additional information as the requirements reach the next level of compliance, as shown in Figure 2.

EXAMPLE 1 In a process based on ISO13407, requirements might be developed to Level 1 during the "Understand Context of Use" activity; to Level 2 during the "Specify Requirements" activity; and to Level 3 during the "Evaluate Designs" activity.
EXAMPLE 2 Requirements might be developed to Level 1 during work on conceptual prototypes; to Level 2 as the user interface design is specified; and to Level 3 for summative testing of the product.

2.2 Level 1 Compliance

Requirements meeting Level 1 compliance include a description of the context of use and identify both the types of criteria and methods to evaluate them that can be used to measure a product’s success in meeting the requirements.

For Level 1 compliance, usability requirements shall:
a. Specify all of the information describing the context of use (see Clause 6.2).
b. Identify relevant criteria for use of the product (see Clause 6.3.1).
c. Identify appropriate evaluation methods (see Clause 6.4.1).

2.3 Level 2 Compliance

Requirements meeting Level 2 compliance add more detailed information about performance and satisfaction criteria, specifying the criteria to be used and identifying target values (or a method for determining those values). At this level, requirements also specify the evaluation methods including a description of how the test will be conducted.

For Level 2 compliance, usability requirements shall:
a. Specify all of the information describing the context of use (see Clause 6.2).
b. Specify evaluation criteria, and target values (see Clause 6.3.2).
c. Specify a usability evaluation method, and identify the context for evaluation (see Clause 6.4.2).

2.4 Level 3 Compliance

For Level 3 compliance, requirements include a specification of target values, that have been validated, for the performance and satisfaction criteria, and a complete protocol for the usability test method.

For Level 3 compliance, usability requirements shall:
a. Specify all of the information describing the context of use (see Clause 6.2).
b. Specify target values for each criterion and user group (see Clause 6.3.3).
c. Specify a complete protocol for the usability test method, as specified in Annex C (see Clause 6.3.3).

3. Normative references

ISO/IEC DTR 9126-2 (2001): Software Engineering - Product quality - Part 2: External metrics
ISO/IEC DTR 9126-3 (2001): Software engineering – Product quality - Part 3: Internal metrics
ISO/IEC DTR 9126-4 (2001): Software engineering – Product quality - Part 4: Quality in use metrics

ISO 9241-11 (1998): Ergonomic requirements for office work with visual display terminals (VDTs) – Guidance on usability

ISO 13407 (1999) Human centred design processes for interactive systems

ISO/IEC CD 25030: Software Product Quality Requirements and Evaluation (SQuaRE) - Quality requirements and guide

ISO/IEC DIS 25062: Software engineering -- Software product Quality Requirements and Evaluation (SQuaRE) -- Common Industry Format for usability test reports

4. Terms and definitions

4.1 usability
the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use [ISO 9241-11:1998]

4.2 effectiveness
the accuracy and completeness with which users achieve specified goals [ISO 9241-11:1998]

4.3 efficiency
the resources expended in relation to the accuracy and completeness with which users achieve goals [ISO 9241-11:1998]

4.4 requirements
expression of a perceived need that something be accomplished or realized [ISO/IEC FCD 25030]

4.5 satisfaction
freedom from discomfort, and positive attitudes towards the use of the product [ISO 9241-11:1998]

4.6 context of use
the users, tasks, equipment (hardware, software, and materials), and the physical and social environments in which a product is used [ISO 9241-11:1998]

4.7 measure (noun)
variable to which a value is assigned as the result of measurement [ISO/IEC 15939:2002]
NOTE The term "measures" is used to refer collectively to base measures, derived measures, and indicators.

4.8 measure (verb)
make a measurement [ISO/IEC 14598-1:1999]

4.9 measurement
set of operations having the object of determining a value of a measure [ISO/IEC 15939:2002, based on the definition in International Vocabulary of Basic and General Terms in Metrology, 1993]

4.10 user
a person who interacts with the product. [ISO 9241-11:1998]
NOTE In this standard users may include current users, potential users, users with disabilities, expected future users, users of the task output, and staff who support or maintain the product.

4.11 user group
subset of intended users that are differentiated from other intended users by factors that are likely to influence usability, such as age, culture, knowledge, skill, expertise, role or responsibility.

4.12 scenarios of use
descriptions of how users carry out their tasks in a specified context.

4.13 stakeholder
a party having a right, share or claim in a system or in its possession of characteristics that meet that party’s needs and expectations. [ISO 15288:2002]
NOTE Stakeholders as used in this standard includes users and user groups

4.14 goal
an intended outcome [ISO 9241-11:1998]

4.15 task
the activities required to achieve a goal [ISO 9241-11:1998]
NOTE 1 These activities can be physical or cognitive.