Can anyone explain how this works?

<font face="arial,helvetica"><font size="2">Hi, <br /><br />I recently posted this same question a few weeks back but
lostthe reply <br />someone kindly sent. The question again how exactly does this query work: <br /><br />it will
returnall attributes and respective data types of a given table': <br /><br />select attname, typname <br />from
pg_classc, pg_attribute a, pg_type t <br />where relname = relation_name and <br />attrelid = c.oid and <br />atttypid
=t.oid and <br />attnum > 0 <br />order by attnum; <br /><br />Many thanks, <br /><br />Rob Burne.</font></font>