I didn´t reply to this thread because I was studying a bit the different alternatives before I go on.
My problem is that I made my first Lazarus system using PostgreSQL, as it´s one of the best rdbms I came across. Yet as it was a simple system, the cost of installing PostgreSQL, and all it´s security in the user´s machine was more or less clumsy, for my intended user type. I could think in some other problems, like what if PostgreSQL was already installed ? how can I made an installer that would install postgresql, verifying this possible installation ? ok it´s possible, but much more complicated that if I just could keep a simple file in the app´s dir. And there are permissions concerns, and the database backup has to use administative privileges of the superuser account, that if it´s already installed could pose be a problem... and I can think in many other problems.
So I go looking for embedded databases preferably one that I could upgrade to full RDBMS capability if and when I need it, and I discovered that the only open-source way to do this (embedded -> full RDBMS) is Firebird.
At first I liked SQLite, due to the support to many platforms, but not having referential integrity, makes it absolutely out of my list.
Also responding Vicent, you´re right, my mistake in the post above. SQL to me is definitively a requirement. What I meant was a RDBMS, not a database.
Anyone knows any other *already working* options ?