A summary of HCI Engineering Design Principles

Stephen Cummaford

Ergonomics & HCI Unit,

University College London,

26 Bedford Way, London,

WC1E 0AP, United Kingdom.

ABSTRACT

There is a need for more formal HCI design knowledge, which can be validated, such that guarantees may be developed. This need would be met by Engineering Design Principles (EDPs). EDPs support the specification then implementation of a class of design solution for a class of design problem within the scope of the EDP.

KEYWORDS:

Engineering, design principles, human-computer interaction.

INTRODUCTION

Current best practice in HCI design has produced many technologies that interact with the user to perform effective work. However, the knowledge applied in the design of these technologies is all-too-often not explicitly stated and so not formally conceptualised, although it may be successfully operationalised by designers. Reliance on such 'craft' skills militates against the identification, and so the validation, of successful design knowledge and, as a result, its take-up and re-use. The lack of validation and the consequent ineffective development of design knowledge thus leads to slow and inefficient HCI discipline progress (Long 1996). There is a need for more formal HCI design knowledge, that is, whose conception is coherent, complete and fit-for-purpose, such that guarantees may be developed and ascribed. HCI Engineering Design Principles (EDPs) would meet this need by establishing these guarantees by means of analytic and empirical testing, leading to their validation.

FUNCTIONAL ROLE OF EDPS

EDPs support the formal specification then implementation of a class of design solutions for a class of design problems. The notions of hierarchical classes of design problem and solution supports carry-forward of design knowledge between similar design instances. Classes are not intended to be a taxonomy of all possible design problems, only those for which a well formed class of design solution exists. SUMMARY OF EDP CONCEPTION

The components of a Design Principle are expressed formally, the relationships between the scope; substantive component; methodological component; and performance guarantees are made explicit such that EDPs may be considered coherent and complete internally (Cummaford & Long, 1998). An important feature of EDPs is the possibility of guaranteeing the successful outcome of EDP application. To support this, the design problems to which an EDP may be validly applied is constrained by the scope. The scope specifies a class of performances which are achievable for a class of users interacting with a class of computers, if the EDP is correctly applied. A design problem is within the scope if the user(s), computer(s)and desired performance(Pd), which comprise the design problem, are instances of the respective classes in the scope. Pd is expressed as product goalsto be achieved (i.e. work to be done) to a certain level of task quality, whilst incurring an acceptable level of coststo the worksystem (Dowell & Long, 1989).

The methodological componentof a Principle supports the specification of a design solution which achieves a desired level of performance by performing a series of task goals. These task goals are sufficient to achieve the product goals specified in the

desired performance of the design problem to a certain level of task quality, whilst incurring some acceptable level of costs to the worksystem. The substantive component specifies worksystem structures and behaviours which are present if the user(s) and computer(s) in the design problem are within the scope. These structures and behaviours are sufficient to perform the task goals specified by the methodological component.

An EDP is conceptualised, operationalised, tested and generalised prescriptive design knowledge, supporting the practices of specification then implementation of a design solution for any design problem with the scope of the EDP. The conception of EDPs presented in Cummaford & Long, it is argued, is coherent and complete. Fitness-for- purpose may only be assessed by empirical testing. Thus, EDPs must be operationalised to support test and generalisation, and so validation. Empirical testing of the implemented system ensures that the principle is fit-for-purpose, that is, it supports the specification then implementation of a system which achieves the desired level of performance stated in the design problem. Furthermore, the explicit scope supports the development of performance guarantees on the basis of empirical testing. The fourth stage of validation, generalisation, involves establishing the generality of the EDP. These four stages of validation support the ascription of a guarantee that a worksystem, which performs the task goal structures specified in the methodological component of the EDP, will attain the achievable performance stated in the EDP. A second guarantee, that the substantive component supports the specification of a worksystem, which exhibits the structures and behaviours sufficient to achieve the task goal structures specified in the methodologicalcomponent, may then be ascribed. A third guarantee, that correct application of the EDP to a design problem within its scope supports the specification then implementation of a design solution which achieves Pd, is then ascribed on the basis of the former guarantees and further empirical testing. EDPs thus support the specification then implementation of a design solution which achieves the desired performance, if the design problem is within the scope of the EDP.

OPERATIONALISATION OF EDP CONCEPTION

A hierarchy of classes of design problem has been hypothesised for Internet-based transaction systems. This is being used to guide EDP development by informing the operationalisation of class-level design problems. When class-level design solutions have been constructed, the task goals sufficient to achieve the product goal stated in Pd will be specified. These task goals will be used to inform development of the methodological component of an EDP and assess Tq. The worksystem structures and behaviours sufficient to achieve these task goals will then be specified and used to inform development of the substantive component of an EDP and assess U and C costs. The proto-EDP will then be operationalised to solve further design problems to support the development of the scope and guarantees.

REFERENCES

Cummaford and Long (1998) Towards a conception of HCI engineering design

principles. Proceedings of ECCE-9, the Ninth European Conference on

Cognitive Ergonomics.in press.

Dowell, J. and Long, J. B. (1989) Towards a conception for an engineering discipline

of human factors. Ergonomics 32,1513-1536.

Long, J. B. (1996) Specifying relations between research and the design of human-

computer interactions. International Journal of Human Computer Studies, 44,6,

875-920.