that's rather a SQL-problem than one of perl.

USE database;

DROP TABLE IF EXISTS taxon;
CREATE TABLE taxon (t_id INT(n) PRIMARY KEY auto_increment,
                    [...]
                   );

DROP TABLE IF EXISTS node;
CREATE TABLE node (n_id INT(n) PRIMARY KEY auto_increment,
                   n_t_id INT(n) NOT NULL DEFAULT 0,
                   [...]
                  );

DROP TABLE IF EXISTS sequence;
CREATE TABLE sequence (s_id INT(n) PRIMARY KEY auto_increment,
                       s_t_id INTn) NOT NULL DEFAULT 0,
                       [...]
                      );
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notice that every record in the node-table, and every record in the sequence-table has to contain the pointer to a record in the taxon-table. the one-to-many relationship will then be realized by something like:

$dbh->selectall_arrayref("SELECT * FROM taxon, node WHERE n_t_id = t_i
+d");
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and the one-to-one realtionship you will find with a query like:

$dbh->selectrow_arrayref("SELECT * FROM node, taxon WHERE n_id = XXX A
+ND t_id = n_t_id");
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how you then wrap that in an object-oriented code is a matter of taste. but basically these are the things that should go on in the background.

greez
TOD