The ".db" looks like a ostorybok private format. It would be nice to have a standard DB, such as sqlite. It would be useful for scripting backups, dumps, etc...

Sorry, the database is a standard one, but not well know, it is a H2database

OK. Difficult to guess, as "file foo.db" does not recognize it (quite unusual, first time in 2 years this command fails for me).

Your DB choice after all, you had surely good reasons.

My 2 ¥:
Difficult to access it beside Java, however, it is somehow locked to a single language (I mean compared to other DB, which could allow C, python, perl, etc)...

H2database was not my choice, but that of Martin Munstum who is the original developer of StoryBook.

Regarding Java, it was precisely because StoryBook was written in Java that I chose it. This choice seems to me to make it easier to distribute and install on different platforms.

As I said: you chose it...

Easier, I don't know. An h2.jar or an XX.jar are still just libs, none is easier than the other for distribution, as long as the underlying DB is stable and use-able.

The only difference is the resulting DB: Either locked to one language, or not.

But what is done is done, it is not so important
I will surely find a way to script the backup the DB properly.

The lib is h2-1.4.189.jar, try to export to sql format. Then check the sql file exported, it's a simple text file. Perhaps it can work with other database system.