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4.2 ISA-95 Summary ToC Previous Next

4.2.4 Modelling Approach of ISA-95 ToC Previous Next

The ISA-95 modelling approach to information is based on a “Property” model. [Note this is an ISA Property not a Property as defined by OPC UA] The ISA-95 models define a minimum set of industry-independent information as attributes. Industry specific, application specific, and company specific information are represented as property objects. For example, the personnel class property would be used to define application or industry specific attributes for personnel classes, and person property would be used to contain instance values for the properties.

In the ISA-95 resource models there are “Classes” and “Instances”. The word “Class” used as part of an object definition name should be considered as a classification, not as a “Class” in the official UML Modelling definition. For example: “Personnel Class” should be considered a “Personnel Classification”, because it is used to distinguish between the kinds of personnel in the real world and to define properties that would be common to personnel within the same classification. The UML description of each of the ISA Information models is described. The ISA-95 Model also includes definitions of common attributes. These definitions are not part of the UML figures, but are included as text in the ISA-95 specification.

Material: is from ISA-95.00.02, it is the ISA-95 material object model. This is the definition of the lots, sublots, material definitions, and material classes involved in production. This information allows Level 3 and Level 4 systems to unambiguously identify material specified in production schedules and consumed or produced in actual production. A prime business driver for using the material model is to provide the ability to trace all materials used in the manufacture of a product to aide in quality analysis and product recalls.

Each Material Definition instance defines a type of material, such as Acetic Acid, grade 4. Each Material Definition may have specific properties, such as pH. These properties can be nested, in that a property can have its own properties. Material Definitions may be assembled from other Material Definitions, as in the case of a sub-assembly in car manufacturing, such as a transaxle which is identified as a Material Definition but is pre-assembled from multiple other Material Definitions. The sub-assembly record keeping is important to maintain traceability.

Material Definitions may belong to a Material Class. Material Classes are used as logical groups to manage Material definitions. Material Classes also have properties that can be nested and may also use the same assembly construct as used by Material Definitions.

Each Material Lot is an instance of a Material Definition that is uniquely identified. Material Lots also have properties that can be nested and may also use an assembly construct similar to that used by Material Definitions, the difference is that a Material Lot may be assembled from other Material Lots and/or Material Sublots. Material Lot instance properties are typically used to track specific shipments or orders of material.

Each Material Sublot is an instance of a Material Definition that is uniquely identified. Material Sublots do not have properties since each sublot instance must have the same properties as the Material Lot it is part of. Material Sublots may also use the same assembly construct as used by Material Lots. Material Sublot instances are typically used to provide tracking resolution within Material Lots, for example a Material Lot may have been received from a vendor in ten barrels, each barrel may be identified as a separate Material Sublot in order to track its movements and environmental conditions during storage and production.

The Material Test Specification identifies a test that may be associated with determining the value for a property of a Material Class, Material Definition or Material Lot instance. The information obtained from running the test can be modelled in the QA Test Result.

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Figure 3 - Material Model

Personnel: Figure 2 is from ISA-95.00.02, it is the ISA-95 personnel object model. This is the definition of the persons and personnel classes (roles) involved in production. This information may be used to associate production with specific persons as part of a production record, or with personnel classes to allocate production costs.

Each instance of the Personnel Class from ANSI/ISA-95.00.02, is the Personnel object model. Each instance of the Personnel Class defines a role that a person can perform, such as a Draftsman. Each role may have specific properties, such as a Drafting License Number and a License Expiration Date. These Properties can also have their own nested properties. Each Person can be associated to one or more Personnel Class Roles. If the person is a Draftsman, then the Person Properties define the values for the Drafting License Number and License Expiration Date for that person. The Qualification Test Specification identifies a test that may be associated with determining the value for a property (such as a test for Draftsman used to obtain a Drafting License Number.) The information obtained from taking the test can be modelled in the Qualification Test Result.

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Figure 4 - Personnel Model

This modelling approach for ISA-95 means that properties must be able to be dynamically queried and browsed. The properties available for individual objects will be different, for example in Figure 22 - Personnel Overview, Joe Smith has a Drafting License Number, but Sally Jones does not.

Equipment: Figure 5 is, from ISA-95.00.02, it is the equipment object model. This is the definition of the roles that equipment and equipment classes perform in production, inventory management, and quality test labs. This information may be used to associate production with specific equipment as part of a production record, or with equipment classes to schedule production and allocate costs

Each instance of the Equipment Class defines a classification of equipment, such as a tank. Each Equipment Class may have specific properties, such as a volume. These properties can be nested, in that a property can have its own properties. Each piece of Equipment can be associated to one or more Equipment Classes. If the Equipment is a tank, then the Equipment Properties define the values for the volume of the tank. Equipment can also be nested, in that they can contain other Equipment. The tank may also include several sensors such as temperature. The modeller can choose between extra properties or next properties and nest equipment depending on their own criteria. The Equipment Capability Test Specification identifies a test that may be associated with determining the value for a property. The information obtained from running the test can be modelled in the Equipment Capability Test Result.

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Figure 5 - Equipment Model

The Modelling approach for ISA-95 results in multiple levels of Equipment and Equipment Classes. By definition if an Equipment is defined by an Equipment Class then it will have Equipment Properties that correspond to the Equipment Class Properties in the defining Equipment Class.

Physical Assets: Figure 6 is from ISA-95.00.02, it is the physical asset object model. This is an identification of the specific physical asset (by serial number or asset ID) used in manufacturing operations. It also includes the make and model information that identifies the type of physical asset and its properties.

Each instance of the Physical Asset Class defines a classification of Physical Asset, such as a valve. Each class may have specific properties, such as a percent open. These properties can be nested, in that a property can have its own properties. Each Physical Asset is associated to one Physical Asset Classes. This relationship is more like a type of, for example a car would be a Porsche 911 Carrera S, and it could not also be any other model. If the Physical Asset is a car, then the Physical Asset Properties define the values for the colour of the car and maybe the option package associated with the car. The option package would have its own properties such as leather interior, sun roof etc.. Physical Assets can also be nested, in that they can contain other Physical Assets. For example a Car would contain four tires that have their own Physical Asset Class. The Physical Asset Capability Test Specification identifies a test that may be associated with determining the value for a property. The information obtained from running the test can be modelled in the Physical Asset Capability Test Result.

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Figure 6 - Physical Asset Model

The Modelling approach for ISA-95 results in multiple levels of Physical Assets. By definition if a Physical Asset is defined by a Physical Asset Class then it will have Physical Asset Properties that correspond to the Physical Asset Class Properties in the defining Physical Asset Class.

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