Some of the technology underneath OPC, particularly OPC Classic, predates or still runs alongside OPC UA. This section covers the legacy and underlying technologies, from DCOM to common data formats, that remain relevant for understanding how OPC implementations work today.
| Term | Definition |
|---|---|
| DCOM (Distributed Component Object Model) | A Microsoft technology that extends COM to allow software components to communicate across networked computers; the original transport for OPC Classic. |
| COM (Component Object Model) | A Microsoft framework for building software components that can interact with each other on the same computer, forming the foundation of OPC Classic. |
| TCP/IP | The fundamental suite of networking protocols that governs how data is addressed, transmitted, and routed across the internet and most modern industrial networks. |
| XML (Extensible Markup Language) | A markup language for structuring and exchanging data in a format that’s both human-readable and machine-parseable. |
| JSON (JavaScript Object Notation) | A lightweight, text-based data format commonly used for exchanging structured data, including in some OPC UA transport encodings. |
| SOAP (Simple Object Access Protocol) | An XML-based messaging protocol used by some OPC Classic web-services-based specifications, such as OPC XML-DA. |
| REST (Representational State Transfer) | An architectural style for designing networked applications, commonly used for web APIs that expose data over HTTP. |
| DDE (Dynamic Data Exchange) | An early Microsoft Windows mechanism for exchanging data between running applications, used for industrial data exchange before OPC existed. |
| API (Application Programming Interface) | A defined set of functions or protocols that allows one piece of software to access the capabilities of another. |
| HTTP (Hypertext Transfer Protocol) | The protocol used to transmit data over the web; relevant to OPC UA’s HTTPS-based transport bindings. |
| ODBC (Open Database Connectivity) | A standard interface for accessing different database systems, commonly used to connect historians or applications to SQL databases. |
| SQL (Structured Query Language) | The standard language used to query and manage data in relational databases. |
| UDP (User Datagram Protocol) | A lightweight, connectionless network transport protocol; used by OPC UA PubSub’s UDP-based messaging mode. |