The database need to have organization details, contacts, groups; forms for input. Also email interface to groups.
Base is just a front end to a database. The database included with Base is an abbreviated version of HSQL. However, you can choose to use a variety of databases such as the full version of HSQL, mySQL, postgreSQL and others.
For more information on Base itself, here is a link to the documentation page: click here.
There are manuals available on the internet for the various databases, ranging from hundreds to thousands of pages long.