Grant execute on functions; related objects permissions ?

Hello,

PostgreSQL 7.3 happily introduced permissions on functions. Now, having
granted execution to a given function to a given user, I find myself with
"access denied" errors on the objects that the function actually uses (e.g.
a table on which it makes a select). So:

1. Am I missing something about how the GRANT ... ON FUNCTION works ?

2. Is there any way to automatically obtain privileges on the objects the
function uses, without having to GRANT specific permissions on those object
(the same way it works on MS-SQL) ?

3. Am I following the wrong direction (I understand question 2. might
actually introduce a permission "hole" on the objects that functions might
use; a user might obtain access to these objects through defining its own
function, am I right ?) ?

Thank you for you help,

Cédric Dufour - Cogito Ergo Soft
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Cogito Ergo Soft - Your think partner