Figure 29provides an overview of the ISA-95 Material handling information model
Material handling includes the definition of a class of material; this class can include material definitions that further define what the material is. These classes of materials are applied to groupings of the actual materials (lots). In many cases these groupings are further broken down into sub-groupings (sub-lots).
Figure 23illustrates the material model which consists of material lots, material sub-lots, material classes, material definitions, and material test specifications.
Typically a class of materials is created and further subtyped into MaterialDefinitionType. These MaterialDefinitionTypes are usually vendor specific versions of the MaterialClassType. From these MaterialDefinitionTypes instances of MaterialLotType or subtypes of MaterialLotType are dynamically created. These instances of a MaterialLotType are maintained in the system for some period of time and then they are removed. For example, a technician may scan a barcode on a just delivered pallet of chemicals; this would cause an instance of the MaterialLotType to be created. This instance of a MaterialLotType may be composed of instances of MaterialSublotType (individual drums of that make up the pallet). When the last drum of chemical used up and all products that were created using the chemicals have been delivered, the system may delete the instance of the MaterialLotType that had automatically been created. In some cases sub types of MaterialLotType may be created, allowing for easier dynamic creation of an instance of a MaterialLotType that is assembled from specific MaterialSublotType(s)
A MaterialDefinitionType defines a specific type of material from a specific supplier. This corresponds to an entry in a corporate Material Master database. For example, it may be stainless steel wire from supplier Ajax Steel, with certain properties, such as hardness and carbon content. A MaterialClassType is a specific type of material without specifying the source of the material. For example, it may be stainless steel wire, with a range of hardness and range of carbon content. The MaterialClassType is used when you don’t care where the material comes from, such as “use any old stainless steel wire”. The MaterialDefinitionType is used when you do care where the material comes from, such as “Ajax Steel stainless steel wire”. Both types are often used in data exchanges.
In many systems the actual instances of MaterialLotType may exist in a database and be referenced by the OPC UA Server (i.e. they may not exist in memory in the OPC UA Server, but the Server would know how to access them and know what instances are available). If a client needs to modify an instance of a MaterialLotType (i.e. change the quantity or some other setting), the Server would handle the update to the underlining database.