This section covers the core OPC and OPC UA specifications themselves — the standards published by the OPC Foundation that define how industrial systems exchange real-time data, historical data, alarms, and more. If you’re new to OPC or want to understand how the different specifications relate to each other, start here.
| Term | Definition |
|---|---|
| OPC DA (OPC Data Access) | Provides real-time access to current process values such as temperatures, pressures, and flow rates from an OPC server. |
| OPC UA (OPC Unified Architecture) | The current, platform-independent OPC standard that combines and modernizes the functionality of the earlier OPC Classic specifications using a service-oriented architecture. |
| OPC HDA (OPC Historical Data Access) | Defines how clients retrieve and analyze previously recorded process data stored in a historian or other data store. |
| OPC A&E (OPC Alarms and Events) | Defines how OPC servers notify clients of process alarms, events, and sequence-of-events data. |
| OPC XML-DA | An OPC Classic specification that exposes Data Access functionality over standard web protocols (XML and SOAP) instead of DCOM. |
| OPC Classic | The original family of OPC specifications (DA, HDA, A&E, and others) built on Microsoft’s COM/DCOM technology, later superseded by OPC UA. |
| OPC Batch | A companion specification for exchanging batch process information, modeled on the equipment hierarchy defined in industry batch standards. |
| OPC Commands | A specification defining interfaces that let clients send and monitor execution of control commands on a device. |
| OPC Complex Data | A companion specification to OPC DA and XML-DA that allows servers to describe and expose complex data types, such as binary structures or XML documents. |
| OPC DX (OPC Data eXchange) | A specification defining how OPC servers exchange data directly with other OPC servers, without a client application in between. |
| OPC Compliance / OPC Certified | Formal certification from the OPC Foundation confirming that a product has passed conformance testing against an OPC specification. |
| OPC Interoperability Workshops | Events hosted by OPC Foundation member companies where vendors test their products against one another to confirm multi-vendor interoperability. |
| Companion Specification | An OPC UA information model built on top of the base UA standard, defining a vocabulary and structure for a specific industry or domain. |
| COTS (Commercial Off-The-Shelf) | Pre-built hardware or software products purchased and integrated with minimal customization, reducing project cost and time. |