If the optional mode is
PX_KEYTOUPPER the key will be converted to lower
or upper case. If mode is 0 or not passed at all,
then the key name will be identical to the field name.
Returns the schema of a database file as an associated array. The key name
is equal to the field name. Each array element is itself an associated
array containing the two fields
type is one of the constants in
table Constants for field types.