Hibernate中oracle常用主键生成策略

<id name="guid" column="guid" type="java.lang.String" length="50" > <generator name="code"><id name="id" column="id" type="java.lang.String" > <generator name="code"> <id name="guid" column="guid" type="java.lang.String" length="50" > <generator class="MsoNormal">?