Background to ISA-95 and MES

Industrial enterprises have in recent years invested heavily in ERP systems. Large investments have also been made in automating the process layer via SCADA systems. The gap between the business automation layer and the process automation layer is where MES systems fit into the picture. ISA-95 is an international standard with the title Enterprise-Control System Integration

The diagram shows a simplified ISA-95 Functional Hierarchy model

What ISA-95 calls integration of enterprise and control systems in practice refers to automating the MES layer plus interfacing the MES system with an ERP system

ISA-95 distinguishes two domains within a manufacturing organisation. The Enterprise Domain (Level 4) and the Control Domain (Levels 3 and lower)

Within the Enterprise Domain, processes with time horizons of years, months, weeks, and days take place. And the scope extends beyond the physical boundary of the location

The term Control Domain stands for a combination of of what is commonly known as the MES layer (Level 3) and the Process Control (PCS) layer (Levels 2 and 1). The scope of the Control Domain is within the factory walls, and activities with time scales of days, hours, minutes, and seconds take place

Object Models

ISA-95's Functional Enterprise-Control Model is depicted in the diagram alongside

The wide dotted line represents the level 3 - level 4 interface

There is quite a lot of overlap between the different information flows shown, and in order to standardize the large amount of information exchanged, ISA-95 has carried out a process of normalization. That is: an analysis of the information flows, determining what the fundamental data are so that standard models for information interchange can be developed, in which the same data only appears once

ISA-95 defines the following basic data: Equipment, Material, and Personnel. These are the basic building blocks of any manufacturing operation, from which information flows can be constructed

In addition to the three basic building blocks, ISA-95 defines the concept of a Process Segement, which is a logical grouping of Equipment Personnel, and Material to carry out a specific part of the process.

The ISA-95 Material Model


Material Classes Material Definitions Material Lots
Material Property Classes Material Definition Properties Material Lot Properties

ISA-95's functional model results in thirty-one information flows, and the normalization of these has led to the emergence of the four resource models (Personnel, Equipment, Material and Process Segment)

In a small, proof-of-concept application, we have focussed on the Material Model and produced a working prototype. As can be seen from the diagram, ISA-95 uses a simplified form of class diagrams in UML. The rectangles define classes of objects; in the case of the Material Model, Material Classes, Definitions, Lots, etc. Lines and symbols connect the objects to each other and clarify their relationships. Next to the lines are comments which make the model fairly easy to read

In putting togther this prototype, we have also embraced another increasingly important industry standard - this time in the software development domain. Together, ASP.NET and MVC enforce a web application software architecture in which the programming code that handles the Enterprise Rules (Model), Presentation (View), and Application logic (Controller) are in clearly separated parts of the application

So go ahead, click on the links above to view, create, update, and delete items in a prototype ISA-95 Materials repository, implemented as a SQL database forming the basis of this application's Model

Acknowledgements