Function
Specifies the system
directory, which is the directory that contains subdirectories holding databases
that you create and the text file derby.properties.
If the system directory that you specify with derby.system.home does
not exist at startup,
creates the directory automatically.
Default
Current directory (the value of the JVM system property user.dir).
If you do not explicitly set the derby.system.home property when
starting , the default
is the directory in which
was started.
You should always explicitly set the value of
derby.system.home.
Example
-Dderby.system.home=C:\
Dynamic or static
This property is static; if you change it while
is running, the change
does not take effect until you reboot.