The OPC Foundation has released a series of standards widely accepted in industry, which enables interoperability in industrial automation:
OPC HDA allows accessing historical data, OPC DA allows accessing current data, and OPC A&E accessing alarms and events.
The reason of the development of OPC UA are manifold:
(i) Unified data access: OPC UA connects the aforementioned standards: Current data, historical data and events are related to each other. OPC UA unifies all these data in its address space.
(ii) Additional requirements: Multiple hierarchies, providing commands and accessing historical data are now possible. Whereas the old specification only provided a single hierarchy with items containing data, OPC UA provides an extensible meta model where those items are typed and multiple hierarchies can .
(iii) Technology migration: The old standards were based on Microsoft’s COM/DCOM technology, which is renewed to the advantage of cross-platform capable Web Services and SOA.
OPC UA specifies an abstract set of services and maps them to different technologies, which promotes platform independence.
(iv) Additional Areas of Applications: With the possibility of mapping the service to different technologies, it is now possible to accessing devices in a performing way as well as providing web services for MES and ERP systems.
The OPC Foundation released an extension of the overall OPC Unified Architecture standards and defines an information model that conforms to ISA- 95.
Figure shows the mapping of the meta-models of OPC UA and ISA-95. Resource and Resource Classes of ISA-95 are mapped as OPC Object with an appropriate ObjectType, properties as Variables with an appropriate VariableTypes.
Process Segments, Operations Definitions as well as other production activities are not covered by the mapping.