The Developer's Guide says in the section titled 'Conventions for specifying the database path':
"When accessing databases from the file system (instead of from memory, the classpath, or a jar file), any path that is not absolute is interpreted as relative to the system directory."
A casual reader might interpret this to mean that the system directory is not used to resolve paths in the names of in-memory databases. But, in fact, Derby does use the system directory to qualify relative paths in the names of in-memory databases.
For instance, if the system directory is /Users/blah/derby/dummy, then Derby treats the following urls as identifiers for the same in-memory database:
Similarly, Derby treats the following urls as names for the same in-memory database:
The Developer's Guide could use a section on how to resolve in-memory database names.