The collection database dictates how data about your collection is stored. Greenstone comes with two database options: GDBM and JDBM. They are essentially the same; JDBM is simply a Java implementation of GDBM. They are flat file database engines. You can select which of these to use in the Browsing Classifiers section of the Design panel.
GDBM (or GNU Database Manager) is a simple flat-file database engine which Greenstone uses as the default database for new collections.
JDBM (or Java Database Manager) is essentially a Java implementation of GDBM. Consider using this database engine combined with the Lucene indexer if you are wanting to create a pure Java run-time.
===== SQLite ===== SQLite is a simple relational database engine. It can be used in Greenstone to provide experimental advanced searching features that are not possible with the other database engines. To enable these features add "sqlform" to the list of SearchTypes in the Format Features section of the Format tab.