1. Download the zip file from OTN
2. Unzip the file in my Applications folder
3. You'll see a folder called "datamodeler"
4. I ran a Terminal session to call this command: sh datamodeler.sh
5. The first time SQL Developer Data Modeler asks you to enter the full pathname of a J2SE installation. For me the path is:
   /System/Library/Frameworks/JavaVM.framework/Versions/1.6/Home
6. Next SQL Developer Data Modeler opens and you are good to go
7. I tried to generate a relational and logical datamodel and it worked great (see below screenshot of the DG Tournament schema
   
   
   

$(function(){
 $('a.htmldbToolbar').parent().parent().css( 'text-align', 'center');
 $('a.htmldbToolbar').parent().parent().parent().parent().css( {'position':'fixed' ,'bottom'  :'0px'
   ,'width' : '100%'})  ;
});

I guess it only works for FireFox, but that doesn't matter, because that's the tool we're all using anyway, aren't we? Oh, yeah, and you need jQuery...

CREATE TABLE tapex_remember_page_item(
application_id NUMBER NOT NULL,
page_id NUMBER NOT NULL, 
item_name VARCHAR2(255) NOT NULL);

-- You don't need to add a UK, however it may be a good idea. 
ALTER TABLE tapex_remember_page_item ADD(
  CONSTRAINT tapex_remember_page_item_uk1
  UNIQUE (application_id, page_id, item_name));
  
-- Since I name all my APEX items in uppercase, just do this as an extra precaution
CREATE OR REPLACE TRIGGER trg_tapex_remember_pg_itm_buir
  BEFORE UPDATE OR INSERT
  ON tapex_remember_page_item
  FOR EACH ROW
BEGIN
  :NEW.item_name := UPPER (:NEW.item_name);
END;
/

INSERT INTO tapex_remember_page_item
            (application_id, page_id, item_name)
     VALUES (20195, 1800, 'P1800_DEPTNO');
            
            
INSERT INTO tapex_remember_page_item
            (application_id, page_id, item_name)
     VALUES (20195, 1800, 'P1800_MIN_SAL');            

DECLARE
BEGIN
  FOR x IN (SELECT item_name
              FROM tapex_remember_page_item) LOOP
    apex_util.set_session_state (p_name      => x.item_name,
                                 p_value     => apex_util.get_preference (p_preference     => x.item_name,
                                                                          p_user           => :app_user
                                                                         )
                                );
  END LOOP;
END;

DECLARE
BEGIN
  FOR x IN (SELECT item_name
              FROM tapex_remember_page_item) LOOP
    apex_util.set_preference (p_preference => x.item_name, p_value => v (x.item_name), p_user => :app_user);
  END LOOP;
END;