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Example of a usability requirements specification This example shows how a usability requirements specification might be written to assist a development team to consider usability in a systematic way during the development process. The usability requirements specification defines the intended context of use and specifies measures and criterion levels for effectiveness, efficiency and satisfaction which must be reached during the development of a product. The specification is based on the framework provided by this part of ISO 9241 for considering the relevant factors. The specification has two main sections which provide the minimal information required about context of use and measures of usability (see clause 5.1.3). The format of the specification closely follows the structure of clauses 5.2 and 5.3 of this part of ISO 9241. The format is not critical and can be adapted, as appropriate, provided the relevant information is provided in a sufficiently precise form. The team involved in producing such a usability requirements specification might typically involve a human factors specialist with experience in usability engineering, and other relevant professionals, for example from marketing, product management and software development. [Comments on the content of the specification are given in italics.] Name and purpose of the product [This section identifies the product and describes its overall purpose.] This specification defines usability requirements for the Videophone professional viewing terminal (VidiPro). The purpose of VidiPro is to increase the effectiveness of telecommunication by providing a combination of voice and visual information. Context of Use [This section provides information following the guidance in clause 5.2 of this part of ISO 9241. Aspects of the context of use are described where these are critical for the usability of the product, for example: Specification of users It is assumed that users are familiar with the most common features of business telephone systems. Some potential users would therefore have to acquire this knowledge before they could use VidiPro successfully. However, no skills or knowledge are assumed with regard to Videotelephony (system knowledge and task experience), and this is explicitly stated. Specification of environments Access to an ISDN socket and mains power are mentioned because without these VidiPro could not be used at all. Specification of equipment The essential parts of VidiPro are listed. This is important where equipment consists of a number of hardware and/or software components, all of which are necessary. Specification of tasks A product such as VidiPro might be used for many purposes. However, the product is intended to help the user to achieve certain particular goals and these are stated here. A number of specific tasks are mentioned where the usability of VidiPro is critical, i.e. installation, call set-up, programming and extended use. At a more detailed level, display legibility is mentioned as this is a condition for usability.] Specification of users VidiPro is intended for use by any person with the following characteristics: | Attribute | Requirement | | Skills and knowledge | | | Product experience | use of business telephone system with "hold", "transfer" and "call diversion" features | | System knowledge | none required | | Task experience | none required | | Organisational experience | none required | | Training | none required | | Keyboard and input skills | use of telephone keypad | | Qualifications | none required | | Linguistic ability | minimum reading age = 11 years1 | | | | | Physical attributes | | | Vision | (corrected) normal vision measured using standard test | | Hearing | normal hearing measured using standard screening test2 | | Manual dexterity | one hand with normal dexterity (VidiPro operable with one hand) |
Notes: 1. For reading help and other information on display. 2. Hearing not required for operation of video features. Specification of environments The following connections must be available: - an ISDN telephone socket
- a mains power supply of 230V +/- 5%
In order to meet the usability objectives, VidiPro should be used in an environment which conforms to relevant ergonomics standards, in particular: - ISO 9241, Part 5, Workstation layout and postural requirements
- ISO 9241, Part 6, Environmental requirements
Specification of equipment The main hardware components of VidiPro are an ISDN telephone terminal, a multiplexer, a video codec, a CCD camera and an 20 cm colour CRT. Specification of tasks The primary intended goal of VidiPro is to enable two users to communicate by voice and to share visual information about objects which are found in an office environment, e.g. sketches, printed text and graphics, maps, photographs and models. Secondary goals of VidiPro include general audio and video communication in an office environment, i.e. without viewing objects. VidiPro could also be used in other environments (e.g. domestic) to provide enhanced interpersonal communication. This usability requirements specification applies to the following specific goals: - Installation: Make VidiPro operational, i.e. ready to make or receive calls, or to be programmed.
- Video call set-up: Set up a video call to enable visual information to be shared.
- Programming: Change VidiPro default setting or information stored.
- Example tasks are to set up call diversion and to enter name and number in the directory.
- Extended use: Communicate by voice and share visual information about objects in an office environment over an extended period
An additional usability requirement for a desired property of the product is: - Legibility: Read system messages and instructions displayed on screen.
Specification of MEASURES OF USABILITY FOR PARTICULAR CONTEXTS [This section specifies the usability goals, targets or objectives for the product by defining both measures and criterion values of the measures for each of the critical tasks listed above. To supplement the general description of the intended context of use, additional information is provided about the specific context of use for each task. At least one measure and criterion value is provided for effectiveness, efficiency and satisfaction following the guidance given in clause 5.3 of this part of ISO 9241. The particular measures chosen and the criterion levels specified will depend on the priorities set by the development team taking the needs and requirements of potential customers into account. In this example the criterion for the efficiency of installation has been specified as completion of the installation task within 10 minutes. (This part of ISO 9241 does not and cannot provide guidance with respect to particular criterion levels.) By producing a specification which follows the guidance of this part of ISO 9241, it is made clear to all parties concerned in what way and under what conditions the product will be usable, and how to check whether this level of usability has been achieved during the evaluation of the product.] Goal:
Make VidiPro operational, i.e. ready to make or receive calls, or to be programmed. Specific context:
Start with VidiPro in original packaging. No additional support or tools are provided.
Users are completing the procedure for the first time. Effectiveness:
Accuracy: All components are correctly connected to each other. Completeness:
VidiPro is connected to a mains power supply and an ISDN line. Efficiency:
Installation to be completed by the user within 10 minutes. Satisfaction:
Less than 10% of users report dissatisfaction with installation procedures. - Video call set-up (initial use)
Goal:
Set up a video call to enable visual information to be shared. Specific context:
Standard on-line and off-line user guidance are available.
Users are completing the procedure for the first time. Effectiveness:
Accuracy and completeness: Called party can see object (e.g. A4 document) within field of view of camera. Efficiency:
Video call set-up to be completed within 2 minutes. Satisfaction:
Less than 10% of users report dissatisfaction with video call set-up procedures. - Programming (initial use)
Goal:
Change VidiPro default setting or information stored:
1) set up call diversion
2) enter name and number in the directory Specific context:
Standard on-line and off-line user guidance are available.
Users may be completing the procedure for the first time. Effectiveness: Accuracy:
No errors in information entered. Completeness:
No omissions in information to be entered or deleted. Efficiency:
Call diversion to be programmed within 2 minutes.
New name and number to be entered into directory within 3 minutes. Satisfaction:
Less than 10% of users report dissatisfaction with programming procedures. Goal:
Communicate by voice and share visual information about bjects in an office environment over an extended period. Specific context:
Users have used VidiPro to share visual information at least 60 times over a period of at least one month. Effectiveness: Accuracy: Less than 2% of all calls placed result in connection to wrong numbers. Completeness: At least 95% of intended calls are completed successfully. Efficiency: Average video call set up time to be no more than 30 seconds. Satisfaction: At least 90% of users prefer VidiPro to alternative equipment, e.g. telephone plus fax machine. Goal: Read system messages and instructions displayed on screen. Specific context: Range of illumination levels from 50 to 5000 lux. Effectiveness: Accuracy: At least 98% of words used in system messages and instructions can be read correctly at normal viewing distance. | 
