Using the <join> element, it is possible to map properties of one class to several tables, when there's a 1-to-1 relationship between the tables.

<join
        table="tablename"
        schema="owner"
        catalog="catalog"
        fetch="join|select"
        inverse="true|false"
        optional="true|false">
        
        <key ... />
        
        <property ... />
        ...
</join>

table: The name of the joined table.

schema (optional): Override the schema name specified by the root <hibernate-mapping> element.

catalog (optional): Override the catalog name specified by the root <hibernate-mapping> element.

fetch (optional - defaults to join): If set to join, the default, Hibernate will use an inner join to retrieve a <join> defined by a class or its superclasses and an outer join for a <join> defined by a subclass. If set to select then Hibernate will use a sequential select for a <join> defined on a subclass, which will be issued only if a row turns out to represent an instance of the subclass. Inner joins will still be used to retrieve a <join> defined by the class and its superclasses.

inverse (optional - defaults to false): If enabled, Hibernate will not try to insert or update the properties defined by this join.

optional (optional - defaults to false): If enabled, Hibernate will insert a row only if the properties defined by this join are non-null and will always use an outer join to retrieve the properties.

For example, the address information for a person can be mapped to a separate table (while preserving value type semantics for all properties):

<class name="Person"
    table="PERSON">

    <id name="id" column="PERSON_ID">...</id>

    <join table="ADDRESS">
        <key column="ADDRESS_ID"/>
        <property name="address"/>
        <property name="zip"/>
        <property name="country"/>
    </join>
    ...

This feature is often only useful for legacy data models, we recommend fewer tables than classes and a fine-grained domain model. However, it is useful for switching between inheritance mapping strategies in a single hierarchy, as explained later.