The first response of the OPC Foundation to the rising limitations related to the adoption of the COM and DCOM architecture was the development of OPC XML-DA. This kept the fundamental characteristics of OPC, but adopted a communication infrastructure that is not linked either to a manufacturer or to a specific software platform. The conversion of the OPC-DA specifications into versions based on web services was not enough to fulfill the needs of factories that increasingly interact and integrate with the corporate and the external world.

The OPC UA was therefore developed with the aim to replace all existing COM-based versions and overcome security and performance issues, satisfying the need for platform-independent interfaces and allowing the creation of rich and extensible data models to describe complex systems without losing functionality. OPC UA is based on a service-oriented approach defined by the IEC 62451 standard. It has the following aims:

• To use OPC components on non-Windows platforms
• To make it possible to embed its core components in small devices
• To implement standard communication through firewall-based systems

From a technical perspective, OPC UA works as follows:

• The API isolates the client and server code from the OPC UA stack
• The UA stack converts the API calls into messages
• The UA stack receives messages by sending them to the client or the server through the API

This is shown in the following diagram: