The technology currently uses DCOM for the communications, which ties it to Windows. The OPC foundation is currently working to transfer the technology to the Web Services platform, under the name OPC UA (Unified Architecture). This work has merely started, and so far only support for data access has been released (OPC XML-DA).OPC-DA (DataAccess) is a specification that deals with how data is sent, such as measurements or text from an OPC server to an OPC client. The information on the server can be grouped by clients, and the groups contain data objects. When a client first asks for an object, the current data is fetched from the data source (another computer or embedded system). Since the data source often is slow, a cache is used. Data is also timestamped.
The client can ask the server for data at any time, but it can also subscribe to the data. When a subscription has been made, the OPC server will automatically transfer the data at a fixed interval.
