DiagramProvider for XML file

When trying to build a diagram based on data from a XML file, an exception occurs,

Caused by: java.lang.UnsupportedOperationException: getInputStream is not implemented in : class com.intellij.uml.UmlVirtualFileSystem$UmlVirtualFile

but the chart is still built.
How to work correctly with an XML file?

And how can you indicate relationships between node elements. Like here 

Now I create relations like here 

but it is not informative when it comes to relations for database fields