High Quality Content by WIKIPEDIA articles! OPC is used by automation professionals for secure data transfer and process control. One OPC specification from the OPC Foundation is OPC Xi (OPC Express Interface). OPC Xi defines a .NET interface with the combined functionality of OPC DA,HDA,AE and a rather simple data model. OPC Unified Architecture in comparison allows the same fucntionality, including a .NET interface and a similar data model to OPC DA, HDA, and AE, but also supports platform independence and optionally complex information modeling capabilities.