3. Introduction to Hierarchical Process Modelling Dr Mike Yearworth
Reader in Systems Engineering
© University of Bristol 2014
HPM idea #1 – Hierarchy
• A system can represented by a network of “blobs” and “links”
• Hierarchy offers us a way of managing complexity • Each level the same but expressed in more detail – decomposi)on
• Decomposi)on is the simple link è Step 1 in the modelling language we will use. There is only one kind of link – a decomposi)on
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HPM idea #2 – Process
• A system can represented by a network of “blobs” and “links”
• The “blob” is conceived as a transformaJonal enJty, a process
• Anything can be a process • Described by verbal nouns (Also known as gerunds -‐ in English these are words ending in –ing.
• They have no subject, and the agent (performer) is not specified) è Step 2 in the common language. There is only one form of blob -‐ a process
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Example of a process hierarchy
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Holon
• Conceptual, abstract, representaJon of a whole, which is also a part
• Used as an conceptual device to think about the world
• Conceptual models that consist of processes, described by verbal nouns, structured into a hierarchical arrangement by decomposiJon and represenJng the minimum processes in a system required to achieve a purpose
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Stimulation of creativity in enactment
• Even physical enJJes can be considered as processes:
“The chair is a process” The chair is enacJng the process “suppor)ng si6er”
• Avoids over specificaJon – I don’t need a chair, I need something on which to sit
• Enables the simultaneous exploraJon of why and how
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Example – the ‘how’ of “designing” ê
Engineering Design
System Requirements & IntegraJon
High Level Engineering ObjecJve
Designing an intercity HS Rail Link
Capturing requirements (passenger nos, travel
Jme)
IntegraJng HS Trains & energy
infrastructure
Procuring COTS HS trains
Building energy supply and distribuJon systems
Defining preferred route and
staJon locaJon
Designing track, bridges, cu\ngs and
tunnel
IntegraJng signalling, track
and trains systems
Designing signalling so]ware
Designing IT network hardware
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Thanks to Dr Ges Rosenberg for this example
Rebalancing*
na+onal*economy**
Providing*IT*
connec+vity*
Providing*
interna+onal*air*
transport*
Delivering*an*
intercity*HS*Rail*
Link*
Financing*and*
planning*for*local*
economic*
development**
Sufficient*other*
necessary*
condi+ons*
Delivering*an*
intercity*HS*Rail*
Link*
Gaining*poli+cal*
support*
Achieving*planning*
consent*(legal)*
Designing*an*
intercity*HS*rail*
link*
Consul+ng*on*
proposals*
Demonstra+ng*
value*for*money*
Financing*HS*rail*
system*
Designing*an*
intercity*HS*Rail*
Link*
Capturing*
requirements*
(passenger*nos,*
travel*+me)*
Integra+ng*HS*
Trains*&*energy*
infrastructure***
Procuring*COTS*HS*
trains*
Building*energy*
supply*and*
distribu+on*
systems*
Defining*preferred*
route*and*sta+on*
loca+on*
Designing*track,*
bridges,**cuMngs*
and*tunnel*
Integra+ng*
signalling,*track*
and*trains*systems*
Designing*
signalling*soNware*
Designing*IT*
network*hardware*
Thanks to Dr Ges Rosenberg for this example
The ‘why’ of designing é
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Examples… modelling electricity supply risk in the UK
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(Marashi & Davis, 2007)
Process of model (holon) building
• The top level process enacts a transformaJon • Challenging system boundary by asking why? • EliciJng system structure through repeated quesJoning of how?
• Layering as required in order to provide meaningful groupings of processes
• Proceeding unJl there is no longer a process answer to the how? quesJon (we are hi\ng unresolved issues)
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Process of model (holon) building
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Why? How
?
Group Model Building: Exercise
• Create a conceptual model of your system starJng from transformaJonal top-‐level process descripJon agreed in the first exercise. Use whiteboards/flipcharts
• Remember to think in terms of – purpose, process, hierarchy, decomposiJon, how (ê) / why (é)
• Present your conceptual model with a view to discussing your system
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References
Blockley, D., & Godfrey, P. S. (2000). Doing it differently : systems for rethinking construc)on. London: Thomas Telford.
Checkland, P. (1981). Systems thinking, systems prac)ce. Chichester: John Wiley. Davis, J., MacDonald, A., & White, L. (2010). Problem-‐structuring methods and project
management: an example of stakeholder involvement using Hierarchical Process Modelling methodology. Journal of the Opera)onal Research Society, 61(6), 893-‐904. doi: 10.1057/jors.2010.12
Koestler, A. (1967). The Ghost in the machine. London: Hutchinson. Marashi, E., & Davis, J. (2007). A Systems-‐Based Approach for SupporJng Discourse in
Decision Making. Computer-‐Aided Civil and Infrastructure Engineering, 22, 511-‐526.
Simon, H. A. (1991). Bounded RaJonality and OrganizaJonal Learning. Organiza)on Science, 2(1), 125-‐134. doi: 10.2307/2634943
Sowa, J. F. (1984). Conceptual structures : informa)on processing in mind and machine. Reading, Mass. ; London: Addison-‐Wesley.
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