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1.5 years afterwards, LNS Research is discussing this concept : ) http://blog.lnsresearch.com/x-questions-from-yesterdays-agile-mes-webinar

Conny Jakobsson

I think this is a very good observation, but I do not fully agree. What I often see, working with ISA-95, is that people mix up the Functional hierarchy with the applications. We have so many times seen the "Automation pyramid" presented to us. In this there is an assumption that there is a one-to-one relationship between functionality (process), application, and often also the device the software run on.

For me, the functional hierarchy is an abstraction, helping us to sort out thing. OK, many time the border between level 4 and 3 often also will be the border between applications, but as ISA-95 points out, it does not necessarily have to be like that. And this pose some problems, of course, for COTS suppliers.

I usually try to leverage the thinking of TOGAF, dividing the solution in Process, Application and Technology layers. The (business/work) processes are what we would like to have performed. The applications are our helpers in realizing this, and the technology layer is the physical realization. Here, virtualization is a big deal today.

In an industrial, shop-floor context, the Role-based equipment hierarchy becomes very relevant. This we must relate to the ideas of Cyber-Physical Systems. The whole factory is such CPS, and so is each work center and work unit. These are containers of functionality. A line controller is a good example of something that is not MES, but is still level 3 - even if it is implemented in a PLC.

My interpretation of role-based equipment is that they are applications in TOGAF terms. Each such equipment (not asset) is represented by some kind of control system. And a control system is not a PLC. The control system software can equally well be run on a PC, server, PLC or why not distributed.

Yes, there is a relationship between ISA-95 functional hierarchy levels and implementations, but we need to try to break free from thinking there is a one-to-one relationship between applications and levels. Then we can come up with even better implementations.

Conny Jakobsson
Industrial Enterprise Architect

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