Process Models

the pages below this one describe the two models for usability assurance (the UMM and the HS model), discuss the integration of the HS model with ISO/IEC 15288 and with other models.

The page on lifecycle discusses the ongoing nature of processes, which is in contrast to stepwise methodologies.

This page gives an introduction to process models.

The first point to note is their scope, which is different to methodologies.

Human Centred Design processes are characterised by multi-disciplinary teams (ISO 13407).  Socio-technical systems theory advocates semi-autonomous teams.  Accordingly, the allocation of function in the UMM and the HS process standard (UMMi) describes the tasks required for a team to deliver usability rather than the tasks that might be expected of a Human Factors specialist.  The processes therefore extend beyond specialist-centred descriptions of ergonomics. 

In the context of business activity, Hammer (1996) points out "The difference between task and process is the difference between part and whole. A task is a unit of work, a business activity normally performed by one person.  A process, in contrast, is a related group of tasks that together create a result of value to a customer....The problems that afflict modern organisations are not task problems.  They are process problems.  The reason we are slow to deliver results is not that our people are performing their individual tasks slowly and inefficiently... We are slow because some of our people are performing tasks that need not be done at all to achieve the desired result and because we encounter agonising delays in getting the work from the person who does one task to the person who does the next one." If Human Centred Design is to be done as multi-disciplinary teamwork (as it must), then we need the work of the team to be specified as process.

Key standards and  models

This paper mentions several ISO standards.The table below provides a quick reference to the key features of the ISO process standards and models used on this site for ease of understanding. The use of  unfamiliar standard numbers has been minimised.  It is expected that much of the readership will be familiar with the  process models from SEI, namely the software CMM® and the system engineering CMMi®

Key process  standards and models

ISO  ref .


Model  name


Ergonomics of human system interaction - Human-centred design processes for interactive  systems

Project  manager's view


Human-centred  lifecycle process descriptions

Usability  Maturity Model (UMM).


A  specification for the process assessment of human-system issues

HS model


Systems  engineering – System lifecycle processes

System processes


Process  assessment

ISO  process assessment framework


Software process – Software lifecycle processes

Software life cycle


Information  technology — Systems Security Engineering


The format for process models such as the UMM and the HS model is specified in ISO 15504. Each process and sub-process is described as follows:

Process  number - for precise reference

Process  name - summary of the process

Purpose  of process - what is done by the process

Outcome - why it is done, the result of successful application of a process

Practices  - what is done to fulfil the purpose

Practice number - for precise reference

Practice name - summary of the practice

Description  of practice - what task is performed

Work products - the items used and produced by the process including the following: pieces of information, documents, hardware, software, training courses, and  awareness in individuals.

Processes should not be confused with the stages of a lifecycle.  Processes are enacted at more than one stage in the lifecycle. The need for a process will vary depending on the stage at which it is performed.  The separation of continuing processes (with clearly defined outcomes to be achieved) from the lifecycle sequence is one of the main differences between process models and methods/methodologies for system design and development.


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