OPC
The OPC specification defines a standard set of objects, interfaces and methods for use in process control and manufacturing automation applications to facilitate interoperability.
OPC servers provide a method for many different software packages to access data from a process control device, such as a PLC or DCS. Traditionally, any time a package needed access to data from a device, a custom interface, or driver, had to be written. The purpose of OPC is to define a common interface that is written once and then reused by any business, SCADA, HMI, or custom software packages.
Once an OPC server is written for a particular device, it can be reused by any application that is able to act as an OPC client. OPC servers use Microsoft's OLE technology (also known as the Component Object Model, or COM) to communicate with clients. COM technology permits a standard for real-time information exchange between software applications and process hardware to be defined.
KNX OPC servers expose the functionality of the whole KNX network to any OPC client. So providing a high level of integration with other systems seamlessly.
Reference:
http://www.opcfoundation.org/ http://en.wikipedia.org/wiki/OLE_for_process_control