ISA-88.

ISA-88, published internationally as IEC 61512, is the standard that made modern batch automation maintainable by separating two things that used to be welded together in controller code. The recipe, which is what to make, and the equipment, which is how a given train runs. Before it, a batch sequence was hard-coded ladder, and changing a product meant editing, re-validating, and re-deploying control logic. ISA-88 defines a physical model, enterprise, site, area, process cell, unit, equipment module, control module and a procedural model, procedure, unit procedure, operation, phase, and it puts the equipment-specific phase logic in the controller while the recipe lives in a database or a batch manager that calls those phases. The payoff is that a new product becomes a new recipe rather than new code, and the validation effort shifts from re-qualifying the whole machine to qualifying one recipe against already-qualified equipment phases, which is why regulated pharma and food manufacturers adopted it most aggressively. On the P&ID the physical-model boundaries are often drawn as labelled unit or equipment-module zones, and those boundaries decide which instruments and actuators belong to which ISA-88 entity, and therefore which phase logic commands each device. That mapping from drawing boundary to equipment module is one of the inputs a commissioning team uses to organize loop folders and the batch function-block allocation, and it starts from a clean, tag-by-tag reading of the set.