<dataConfig>
<dataSource driver="org.hsqldb.jdbcDriver" url="jdbc:hsqldb:/temp/example/ex" user="sa" />
    <document name="products">
        <entity name="item" query="select * from item">
            <field column="ID" name="id" />
            <entity name="feature" query="select description from feature where item_id='${item.ID}'">
                <field name="features" column="description" />
            </entity>
            <entity name="item_category" query="select CATEGORY_ID from item_category where 
                                                                              -- !! must reference parent entity's PK by field column, not by field name !!
                                                                              item_id='${item.ID}'">
                <entity name="category" query="select description from category where id = '${item_category.CATEGORY_ID}'">
                    <field column="description" name="cat" />
                </entity>
            </entity>
        </entity>
    </document>
</dataConfig>