OPC Labs runs a public demonstration OPC XML-DA server that you can use for your explorations and tests. The server's URL is http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx . Our example code also refers to this server, so that the examples can be run without having to set up a server locally.
The server is based on the sample server code from OPC Foundation. It provides some OPC data of its own, and it wraps two OPC COM-based servers (OPC-DA 2.0 and OPC-DA 3.0). It contains a combination of items of various data types, static and dynamic, some readable and some also writeable.
OPC XML does not define a way for server discovery (browsing for servers). For this reason, if you are using user interface components such as the browsing dialogs or controls, you need to specify the server manually, using its URL. To do so, select the "Any Computer" node in the dialog or control, and then click either the "+" sign in the toolbar of the dialog, next to the drop-down list that says "OPC Server", or right-click the "Any Computer" node, and select the "Add Node" command from the context menu, or press the Ins (Insert) key. You can then type in the server URL, and press Enter.
Once you have specified the server URL, you can work with it like with a COM-based OPC server. The are only minor differences - for example, each node in OPC XML also has an additional identifying piece of data, the so-called "Node path" (item path), which is now displayed in the information pane as well. The other difference is that the OPC properties are identified by XML qualified names, and the browsing UI has been enhanced accordingly:
Using the XML-enabled demo application that ships with QuickOPC 5.31+, you can immediately connect to this public demo server, and do the browsing, get property values, read and write items, and subscribe to a single item: