Database Files Extensions - What are database files and how do I open a database file?

What are database files and how do I open a database file?

File Type Category File Format
.4dd Database Files 4th Dimension Database Data File
.adb Database Files Alpha Five Database File
.adx Database Files Approach Index File
.btr Database Files Btrieve Database File
.cct Database Files Director Protected Cast Resource
.cdb Database Files Symbian Phonebook Database
.ckp Database Files SQL Server Checkpoint File
.db Database Files Database File
.db3 Database Files SQLite Database File
.dbc Database Files FoxPro Database
.dbf Database Files Database File
.dbs Database Files SQLBase Database File
.dlc Database Files Download Link Container File
.dnl Database Files DNAML eBook File
.dtsx Database Files DTS Settings File
.fdb Database Files Portfolio Catalog
.frm Database Files MySQL Database Format File
.fxp Database Files Adobe Flex Project File
.hdb Database Files HansaWorld Database File
.itdb Database Files iTunes Database File
.lbl Database Files NiceLabel Template File
.mpd Database Files Microsoft Project Database
.pdb Database Files Program Database
.sql Database Files Structured Query Language Data File
.sqlite Database Files SQLite Database File
.sqlitedb Database Files SQLite Database
.v12 Database Files All The Right Type Database File