Hi Martin,

In what way does the program or the system know that
"the police report has arrived"? Is there e.g. a certain file
available in a certain location?

Yes, when PoliceReport.xml arrives it is placed in the same folder as the

Well, Java can "watch" a directory for changes see e.g.
https://docs.oracle.com/javase/tutorial/essential/io/notification.html
so it is certainly possible to implement something in Java but I have no
idea how such a function would fit into Saxon's use of Java extension
functions to XSLT/XPath/XQuery; perhaps Michael Kay shows up later and
can tell you more.