Which version of OPC is indicated by the term Unified Architecture?

The term "Unified Architecture" specifically refers to OPC UA, which is the modern and advanced version of the OPC standard. OPC UA was developed to provide a robust and secure framework for industrial automation and data exchange that accommodates today's complex networking and security requirements.

OPC UA is platform-independent, designed to work across various operating systems, and supports various programming models, making it suitable for both small devices and large enterprise systems. This architecture integrates multiple features into a single framework, including data modeling, security, and information exchange, all in a way that is easily consumable in different environments.

In contrast, the other terms relate to previous versions of the OPC standard. OPC DA and OPC Classic refer to earlier versions that are tied to COM/DCOM technologies, making them less versatile in today's diverse networking environments. OPC XML-DA is a specific implementation that utilizes XML for data exchange, but it does not encompass the full range of capabilities and features included in the Unified Architecture of OPC UA. Hence, the correct association of "Unified Architecture" is indeed with OPC UA.