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Human-Systems Model

The  Human-Systems model in ISO PAS 18152 (termed UMMi by Tom Metzler) was developed with the following objectives in mind:

  • To provide the means of assessing and mitigating risks arising from human-system issues that will affect usability through the life cycle, both at transition points between life cycle stages and during each stage.
  • To provide a description of human-system processes for use in project planning and  for inter-disciplinary communication.
  • As a basis for understanding and co-operation during the tendering process and for  human-system capability evaluation to support contract award, either in a stand-alone manner or in conjunction with a software or system capability  evaluation.
  • To provide a basis for structured human-system process improvement by supplier,  customer or employer organisations.

The  MOD proposed an approach based on International Standards to support  international procurement during acquisition and also multi-national operations  during the operational phase.  

One  of the objectives was to alter the business model underpinning fixed-price  competitive procurement by assisting companies that adopt a human-centred  approach to succeed against organisations that minimise Unit Purchase Cost at the expense of Whole Life Cost.

The  HS model has been written with the interests of the project in mind, rather than  acting as a lobby for HF specialists.   The authors accepted the challenge from a number of stakeholders to  remove all HF specialist "push" and to define activities in terms of what the  project needs, rather than what specialists would like to be paid to do.   This led to a significant change in emphasis and terminology, but must be the right approach for a discipline that preaches  user-centredness.  

During the early stakeholder analysis for the model, it was recognised that there was still some way to go in bringing together the business of 'putting the machine in front of the user' (typically Human Engineering) and the business of 'putting  the user in front of the machine' (typically selection and training).   The system acquisition impact of changes in trade structures, use of reservists, contractorisation and conditions of employment have been found difficult to resolve within the context of an acquisition project.   This recognition  led to the introduction of a Human Resources process (HS.4), a development that goes to the heart of HSI by explicitly linking manpower and personnel with system acquisition.   So far as the  authors are aware, the HS model is the first model to represent this  linkage.

The  HS model is complementary to the 7 HSI domains.   The domains define the scope of application and the model defines what  needs to be done.   The scope of the HS model is to describe the activities necessary to deliver and maintain  operability.   The emphasis is on describing the job to be done and the outcomes to be achieved from multi-disciplinary teamwork, taking advantage of the rigorous ISO format for describing processes.

Content of the HS  model

The  HS model has four processes, each with a number of sub-processes as set out in  this page (click here to see a summary of the model).


HS.1 Life cycle  involvement

(Human-system issues in:)


HS.1.1 Conception

HS.1.2 Development

HS.1.3 Production and  utilization

HS.1.4 Utilization and  support

HS.1.5 Retirement


HS.2 Integrate human factors


HS.2.1 Human-system issues in business strategy

HS.2.2 Human-system issues in quality  management

HS.2.3 Human-system issues in  authorisation and control

HS.2.4 Management of human-system issues

HS.2.5 HF data in trade-off and risk mitigation

HS.2.6 User involvement

HS.2.7 Human system  integration

HS.2.8 Develop and re-use HF data


HS.3 Human-centred design



HS.4 Human resources


HS.3.1 Context of use

HS.3.2 User requirements

HS.3.3 Produce design solutions

HS.3.4 Evaluation


HS.4.1 Human resources strategy

HS.4.2 Define standard competencies and  identify gaps

HS.4.3 Design staffing solution and  delivery plan

HS.4.4 Evaluate product system solutions and obtain feedback

The  first process addresses the needs of the life cycle.   The second process addresses the various  interfaces to the organisation.   The third comprises the iterative technical cycle, and the fourth addresses the  timely delivery of trained operators.   They are:

HS.1.  Human Factors in the Life Cycle.   This process anticipates and tracks the particular needs of each stage in the life cycle.   The intent is to improve the  efficiency of the life cycle by timely resolution of human-system issues.  

HS.2.  Human Factors Integration. This process is concerned with strategy, procurement, planning and integration with mainstream engineering processes. It ensures that human-system issues are addressed by the appropriate stakeholders.   It reduces life cycle costs by ensuring that  “design for people” is used within the organisation.   Because user involvement is both crucial to  success and almost always difficult to achieve, a sub-process is devoted specifically to this (HS.2.6).   This is also where specialist Human Science knowledge is brought to bear (HS.2.8).

HS.3.  Human-centred design. This process is technical, concerned with requirements, design and evaluation.   It enables  user-centred technical activity to be focused appropriately.   It contributes to a 'better' system by the  inclusion of processes that deliver usability.   It is a development of the technical processes of HCD.

HS.4.  Human Resources process. This process is concerned with selection and training, and harmonising organisational development and technological change. It provides the means to resolve issues concerned with the “implementation” of the human part of the system, rather than the equipment-centred part.   It ensures continued, timely delivery of the correct number of competent people required to use the most suitable equipment.

The  first three processes have been the subject of extensive international  review.   The last process is considered to have received less review.   However, it has been found that in initial use of the model, HS.4 has met with the most enthusiastic response and endorsement.   In part, this reflects options at different stages of the life cycle; when a system is operational HS.4 represents the main process for making improvements, since design changes are much less affordable.

Contents of the Human-Systems model standard (ISO PAS  18152)

ISO  PAS 18152 is written with a degree of rigour unusual in Human Factors.   After providing statements of introduction and scope, it gives a comprehensive set of definitions.   The main body of the standard presents a  reference model that describes the processes HS.1 to HS.3 and their sub-processes.   Each description presents the purpose of the (sub-)process, what will be achieved if it is performed (the  outcomes) and lists the practices by which these outcomes are achieved.   HS.4 is presented in an annex.   Descriptive notes on each practice and a list of the work products used by and produced by the process are provided as an assessment model (Annex A).

The  technical components of the model are described, with the relationship between  the processes in the model, the lifecycle and the organisation.   The context to assessment, process standards  and HSI is outlined.  

Further  annexes provide the following:

  • The  use of the HS model in process definition, improvement and  assessment.
  • Indication of which practices in the HS model are evidence of organisational maturity greater than level 1.
  • The  interrelationship between the processes and work products in the HS model.
  • Mappings between the HS model and ISO process standards for HCD and the system life  cycle.
  • A  conformance statement for the HS model against the ISO 15504 process assessment standard.



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