The The Resource-Event-Agent business ontology (REA) was developed 1982 from William McCarthy. REA, which is used in ISO 15944-4, proposes concepts and patterns to derive semantic models of economic exchanges and transformations.
The underlying assumption is, that business enterprises acquiring financial resources, engaging in a chain of economic exchanges with other parties. Each time they give up an economic resource in return for another resource of greater value. In order to model economic exchange, REA proposes three main objects, which are shown in Figure on the left:
- Resource are exchanged between the agents: e.g. commodities and assets.
- Event triggers the executing economic activities.
- Agent gains access to an resource of another agent in exchange to giving up control of another resource.
The following axioms are premised:
- At least one take event and one give event exist for each economic resource, which guaratees an exchange.
- An Event, which triggers a resource decrement must be eventually paired in duality relationships with events effecting an increment and vice
- Each exchange needs an inside and an outside agents, which ensures an exchange between two competing parties.
The right side of figure shows a very simple object constellation of a fish sale. A customer receives via FishSale from a salesperson a fish. Therefore he provides a cashier cash via payment. The fishSale is an decrement of fish, and the payment is an increment of cash.
Figure shows the high granular metamodel of the REA Duality, which was extended with several concepts: e.g. commitments, schedules, policies. Commitment for example enables the planning layer equivalent of events: It contains information about what has been agreed on in the future, which are fulfilled by events.
Besides, the type-object, also known as powertypes, pattern is used. This offers, that there is for each entity a type class and class available e.g. Resource Type Classes are as well as Resource Class. The type-object submodel is depicted with gray shading. The upper part contains the type layer (realized with powertype concept of UML) – the lower part the object layer.
Now, we want to give a short version of the main idea of the mapping of the metamodels of REA and ISA-95. The mapping of the entities includes the integration of their attributes.
- Resource Type is mapped on Physical Asset Class, Equipment Class, Material Class and Material Definition.
- Resource is mapped on Physical Asset, Equipment, Material Lot and Material Sublot. Linkage realizes the relationships of Material Class, Material Definition, Material Lot and Material Sublot.
- Agent and Agent Type can be mapped on Personnel Class and Person.
- The Process Segment corresponds to the Type Layer, because it is more generic and does not adress a specific production run. A Process Segment is therefore equivalent to Transformation Reciprocity and Duality Type. The attached Commitment or Event Type has the following Participation Type, which can be mapped on Personnel Segment Specification, and Planned Stockflow Type, which can be mapped either on Equipment Segment Specification, Physical Asset Segment Specification or Material Segment Specification.
- Operations Definition is a Schedule Type – the Schedule an Operations Request.
- Transformation Reciprocity can mapped on Segment Requirement – Transformation Duality on Segment Response. The attached entities can be transformed with the same concepts of the axiom before.