The major difference between PI and MES models are that PI is primarily data centric whereas MES is centered on orders/work requests. So data models in PI are most commonly developed around the physical structure and layout of the plant or the process and don’t need to follow any specific conventions. On the other side MES data structures need to be compliant to the Enterprise Resource Planning (ERP) data structure that they are communicating with.
The two main standards for MES data structures are ISA 95 and ISA 88. The following Wiki links give a short explanation with the main references:
ISA 95 is a general standard for interfacing ERP and control systems, whereas ISA 88 is specific to batch systems. The ISA 95 and ISA 88 equipment models can be merged to include the batch structure.
The following shows a combined equipment structure that is often used as a template for the equipment structure:
In PI the same structure can be created using Element templates and references. Best practice is to start with a base template and then derive the different equipment level templates from it. The reference types enforce the hierarchy and help to guide the development.
The following file contains the full S95\S88 equipment structure as seen above with the corresponding reference types: