OPC Unified Architecture
OPC Unified Architecture (OPC UA) is targeted for Service Orientated Architectures (SOA), enterprise architectures and applications built by combining loosely coupled and interoperable services. What the original OPC Data Access (OPC DA) specification was to COM, OPC UA is to Web Services, except UA encompasses a much larger scope. Regardless of ‘What’ type of information you wish to move, OPC UA describes ‘How’ to achieve this. The OPC UA documentation is a set of layered specifications broken into multiple parts. It is purposely described in abstract terms in the Base and Functional Parts and in the Implementation Parts, is integrated with existing technology on which OPC UA products can be built. This layering is purposely intended to isolate changes in the OPC UA specification from changes in the technology used to implement it.[1]
This multi-layered approach accomplishes the original design specification goals of:
- Functional equivalence: all COM OPC Classic specifications are mapped to UA
- Platform independence: from an embedded micro-controller to cloud-based infrastructure
- Secure: encryption, authentication, and auditing
- Extensible: ability to add new features without affecting existing applications
- Comprehensive information modeling: for defining complex information[2]
Although developed by the same organization, OPC UA differs significantly from its predecessor, Open Platform Communications (OPC). The Foundation's goal for OPC UA was to provide a path forward from the original OPC communications model (namely the Microsoft Windows-only process exchange COM/DCOM) that would better meet the emerging needs of industrial automation. After more than three years of specification work and another year for a prototype implementation, the first version of the Unified Architecture was released in 2006. The current version of the specification is on 1.04 (22 Nov 2017). The new version of OPC UA now has added publish/subscribe in addition to the client/server communications infrastructure.[3]