Interestingly, that's exactly what I did in the first versions of auto_coder.

One of the problems with this approach is that we don't have an easy way to define broader project properties -- we're too focused on the database design.

Moreover, we must write different scripts for different databases; with XML we can write a single source and generate different scripts.

Another advantage of XML is the avaibility of modules like XML::Simple, which translates a XML source into a Perl data structure like this:

$VAR1 = {
          'table' => [
                     {
                       'descriptor' => 'name',
                       'caption' => 'contact',
                       'name' => 'contact',
                       'field' => [
                                  {
                                    'notnull' => '1',
                                    'caption' => 'first name',
                                    'name' => 'name',
                                    'type' => 'varchar',
                                    'size' => '40'
                                  },
                                  {
                                    'visible' => '1',
                                    'caption' => 'organization',
                                    'name' => 'organization',
                                    'type' => 'varchar',
                                    'size' => '40'
                                  },
                                  # ...and so on.
[download]

In other words, extending SQL with comments *was* my first approach, but it had its shortcomings.