dOPC was one of the first Client Toolkits worldwide which supported the OPC XML DA version 1.x specification created by the OPC Foundation (http://www.opcfoundation.org). The OPC XML DA specification can be downloaded there.
The OPC XML DA specification is based on Web Services instead of COM/DCOM. Web Services are based on http as transport layer as well as SOAP and XML. The OPC XML DA specification does not replace OPC COM, but is rather an extension of the present OPC COM DA specification.
OPC XML-DA provides several additional benefits:
However, as a dOPC developer you can easily change to XML DA communication. Instead of choosing the 'normal' server name (property ServerName in the TdOPCDAClient class) in your program just precede the server name with "http://..." to instruct dOPC to use XML connections. Apart from that the handling is the same as with a 'normal' OPC COM DA server.
If you would like to learn more about the OPC XML protocol I recommend the dOPC demo program's OPCXMLCore. It has been developed without the dOPC DA component and only uses the pure XML DA protocol.
If you want to develop a none Windows OPC XML DA client program then you have to change the default XML vendor to: sOmniXmlVendor at the beginning of your application.