How can I handle 1:1 relationships?

Hello all,
I've problems  to handle 1:1 relationships, I want this association is 
navigable on both sides, from person to passport and vice versa.
I'm working with OJB and Postgresql, how can i declare in the ojb 
descriptor, in the schema this type of relationships, i try this way, 
but i get the following error:
proxy.IndirectionHandler - Can not materialize object for Identity 
org.apache.ojb.Person{25} - using PBKey org.apache.ojb.broker.PBKey: 
jcdAlias=default, user=postgres, password=*****
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and to remove it shows:
java.lang.NullPointerException
       at 
org.apache.ojb.broker.core.PersistenceBrokerImpl.doDelete(PersistenceBrokerImpl.java:608) 

       at 
org.apache.ojb.broker.core.PersistenceBrokerImpl.deleteReferences(PersistenceBrokerImpl.java:803) 

       at 
org.apache.ojb.broker.core.PersistenceBrokerImpl.performDeletion(PersistenceBrokerImpl.java:674) 

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My schema.sql is thus:

CREATE TABLE Person
(
   person_id         INT NOT NULL PRIMARY KEY,
   person_name        VARCHAR(60),
)

CREATE TABLE Passport
(
   person_id       INT NOT NULL PRIMARY KEY,
   passport_number VARCHAR(20),
   foreign key(person_id) references Person(person_id) on update CASCADE 
on delete CASCADE
)

In my ojb descriptor I have the following:

<class-descriptor class="org.apache.ojb.Passport" table="PASSPORT">
     <field-descriptor name="personId" primarykey="true" 
nullable="false" column="PERSON_ID" jdbc-type="INTEGER"/>
     <field-descriptor name="passport_number" nullable="false" 
default-fetch="true" column="PASSPORT_NUMBER" jdbc-type="VARCHAR"/>
     <reference-descriptor name="personIdRef" 
class-ref="org.apache.ojb.Person" auto-update="false" 
auto-delete="false" proxy="true">
         <foreignkey field-ref="personId"/>
       </reference-descriptor>
   </class-descriptor>
****************************************************************
<class-descriptor class="org.apache.ojb.Person" table="PERSON">
       <field-descriptor name="personId" primarykey="true" 
nullable="false" autoincrement="true"... column="PERSON_ID" 
jdbc-type="INTEGER"/>
     <field-descriptor name="personName" nullable="false" 
default-fetch="true" column="PERSON_NAME" jdbc-type="VARCHAR"/>
       <reference-descriptor name="personPassIdRef" 
class-ref="org.apache.ojb.Passport" auto-update="true" 
auto-delete="true" proxy="true">
         <foreignkey field-ref="personId"/>
       </reference-descriptor>
</class-descriptor>

Thanks in advanced.

-- 
Iris Soto