為啥我按照步驟做下來，沒有property呢？

<?xml?version="1.0"?>
<!DOCTYPE?hibernate-mapping?PUBLIC
"-//Hibernate/Hibernate?Mapping?DTD?3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
??<class?name="Students">
??</class>
</hibernate-mapping>

咋回事呢？