The Interoperability Workshops are events hosted by the OPC Foundation that allow OPC vendors to test their OPC products with each other. These events are held three times a year at different locations (The US, Europe and Japan).
The OPC Foundation has created a set of standard Interoperability Tests for each specification. The OPC vendors are expected to run these tests for each combination of an OPC client product and OPC server product that is available at the workshop. The results of these tests are then made available in the OPC product catalogue.