Extending classes

[Jez]

I've created a database export class with extensions for exporting to
csv, xls, html and xml. The file export.inc.php contains the 'export'
class which deals with getting the data and storing the field names
and row data in arrays - used for all exports. export_csv.inc. php
include()s export.inc.php and contains 'export_csv' which extends the
export class, formatting the field name and row arrays as a csv file
and sending the file to the browser. There are other similar
extensions for xls, html and xml.

At the moment I have to do something like this to get my exported
data:

switch ($type) {
case "csv":
include("path/to/export_csv.inc. php");
$export = new export_csv();
break;
case "xls":
include("path/to/export_xls.inc. php");
$export = new export_xls();
break;
...
}

$export->get_data($dbho st,$dbname,$dbu ser,$dbpass,$sq l);
$export->output();

That seems quite untidy and what I'd really like to do is this:

include("path/to/export.inc.php" );
$export = new export("csv");
$export->get_data($dbho st,$dbname,$dbu ser,$dbpass,$sq l);
$export->output();

I know it must be possible because that's how ADODB selects its
drivers, but I can't get my head round how it works. Any idea how I
should go about organising my classes and their separate files? Has it
got something to do with the 'factory method' that I've seen mentioned
in a few places recently?

Hope that makes sense?

Thanks!

Jez