I was somewhat shocked at the Emerson Global Users Exchange a few weeks ago to see a booth with several well-known OPC suppliers–but it wasn’t the OPC booth. They were touting a new communication protocol called “Xi” for Express Interface. It was briefly explained to me as an OPC UA “lite.”
OPC UA is the new protocol, kind of long coming out, where the OPC Foundation is taking its well-used protocol suite and moving it from a Microsoft-centric COM/DCOM foundation to a more contemporary and open XML standard. OPC is used in many applications for moving data from the control layer to the manufacturing software layer, e.g. HMI/SCADA and MES. The new UA standard builds on the relatively simple previous version by adding many new functions to enable enterprise software connectivity.
Trouble is, some suppliers really don’t want all that overhead. They want something simple and quick. So a bit of a battle began over whether to release UA at the simpler level of OPC DA or whether to wait until the full blown spec gets done. Emerson Process Management didn’t want to wait–and it wanted the simpler version. So it developed Xi. It brought in partners. I was told by Emerson executives that they would gladly give it to OPC Foundation in order to expedite the process of having this lighter spec. On the other hand, Xi is Microsoft-centric again, built upon dot Net.
Things are progressing. OPC Foundation President Tom Burke reports in his blog about negotiations to bring the spec to the Foundation. Interestingly, Eric Murphy of the OPC Exchange blog by Matrikon wrote a detailed post about Xi. I received it via RSS feed, but when I clicked the link to go to the Web page to copy into this post–poof, it was gone. Too bad. It was a nicely reasoned piece.
Anyway, watch for this Xi spec to simplify and speed up a certain level of connectivity. But if you want further connectivity, press your supplier to get the entire UA implementation done.