Is it possible to use SQLite as a relational database from Google App Engine? (Java) I need read/write access to it from the app itself.
Also, I am using Quercus for PHP, and if what I am asking for is possible, I can handle storing the database myself.
No, it is not possible. This would require write access to the filesystem, which App Engine does not allow.
SQL database support (MySQL like) is planned, but no release data has been given. For now, use the datastore.