无ID的po,在hibernate里怎么配置?

如题
我是如下配置的:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!--
    Mapping file autogenerated by MyEclipse - Hibernate Tools
-->
<hibernate-mapping>
    <class name="tv.dogo.po.VideoLabel" table="VIDEO_LABEL" schema="DOGO">
    <id/>
        <many-to-one name="videoInfo" class="tv.dogo.po.VideoInfo" fetch="join"  >
            <column name="VIDEO_ID" precision="22" scale="0" />
        </many-to-one>
        <many-to-one name="labelInfo" class="tv.dogo.po.LabelInfo" fetch="join" lazy="false"  >
            <column name="LABEL_ID" precision="22" scale="0" />
        </many-to-one>
    </class>
</hibernate-mapping>

但是总是报错:Unknown entity: tv.dogo.po.VideoLabel
any ideas?谢谢

id是必须的,我搞错了,呵呵