One-to-one mapping in hibernate

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XML

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mapping

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<hibernate-mapping>
    <class name="hibonetoonehbm.Student" table="student">
        <id name="studentId" column="StudentID" type="long">
            <generator class="native"/>
        </id>
        <property name="studentName" column="StudentName" type="string" length="50"/>
        <many-to-one name="studentAddress" column="StudentAddress" cascade="all" unique="true" not-null="true"/>
    </class>
</hibernate-mapping>

In the above code we perform one-to-one mapping using <many-to-one> by setting unique="true". There is also a <one-to-one> tag. Could anyone explain me why <many-to-one> tag is used for one-to-one mapping even if <one-to-one> tag exists ?

What I have tried:

I tried using <one-to-one> tag but there is no 'column' attribute in <one-to-one> tag :(