Collect simple software objects; don’t make all objects complex

Collect simple software objects, suggests Francis Lovering with Control Draw (www.controldraw.co.uk) and involved with ISA88 more than 10 years. He says there’s no need to make all objects complex. The next few postings will offer comments on ISA88 Part 5, draft 5. (ISA88, Batch Control, Part 1 Models and Terminology, is being revised to help those outside of batch control understand and use the standard more effectively. Being drafted now, Part 5 of the standard is "Implementation Models & Terminology for Modular Equipment Control.")

Francis responded to some prior comments from Bob Steele here: ISA88 Part 5, draft 5: Resource manager allows one control to own another.

Francis continues: "Complexity is in the nature of automation; however, it can be achieved by assembling a collection of simple objects, not by making all objects complex. I do understand Resources and I don’t think that they have a place in basic control at all. Resources are what a Recipe manager for example uses to assemble the actual equipment that meets the Equipment Requirements for the recipe, from the pool of available equipment.

"I see no advantage to delegating any of this down to control modules (or even Equipment Procedural Entities). I suggest that your (shall we say) conversion to the “Part 5 models” with all their complexity is something that you would be better to forget, because there are many alternative and simpler models that have not been presented to you but that would have achieved all the functionality that Part 5 is attempting to achieve.

"I guess the core of this argument is about the freedom of designers to design, and I am concerned that Part 5 is likely to undermine that, and in the end have exactly the opposite result than its goals. Committees are not good at designing."

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