Flat file databases [closed]

Well, what is the nature of the flat databases. Are they large or small. Is it simple arrays with arrays in them? if its something simple say userprofiles built as such:

$user = array("name" => "bob", 
              "age" => 20,
              "websites" => array("example.com","bob.example.com","bob2.example.com"),
              "and_one" => "more");

and to save or update the db record for that user.

$dir = "../userdata/";  //make sure to put it bellow what the server can reach.
file_put_contents($dir.$user['name'],serialize($user));

and to load the record for the user

function &get_user($name){
    return unserialize(file_get_contents("../userdata/".$name));
}

but again this implementation will vary on the application and nature of the database you need.