dbs/db4/xdn_trace_file is a SAP Parameter attribute which is used to control Trace file created by XDN information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
dbs/db4/xdn_trace_file denotes the constant prefix from which the file
names are calculated, which XDN uses to trace to. The value is either a
path relative to the current work directory ($DIR_HOME), or an absolute
path (if it starts with a "/" or a "\").
This parameter only has effect, if
See SAP Parameter Documentation for full SAP documentation for this profile parameter.