Base can connect directly to most relational databases, such as MySQL, PostgreSQL, Oracle, Adabas D, or any database that supports the Open Database Connectivity (ODBC) or Java database connectivity (JDBC) drivers. So it also functions as a graphical front-end to other databases, and you can use it to edit and change them. Address books, spreadsheets, and delimited text files are read-only. You can import their data into Base, but whenever you make a change to the source document you have to import the new data; you can't change it or directly access it from Base.
My contacts are in a KDE address book. Importing this into Base is so easy your cat can do it:
"Family Name","Given Name","Honorific Prefixes","Home Phone", "Home Fax","Home Address Street","Home Address City", "Home Address State","Home Address Zip Code" "Schroder","Carla","Ms.","","","5678 EndOfTheLineLane", "Red Cowtown","Oregon","54321"
Even though there are line breaks for readability, the real line breaks are at the ends of the lines with no commas. You have to have the exact same number of fields in your field definitions line, which is the first line in the file, and in your data lines. In this example there are nine. Any empty fields need "" for a placeholder, and each field is separated by a comma. You can use a comma, single space, tab, colon, or a semi-colon for the delimiter.