You can use the id and href attributes to multi-reference a value of the address element, as shown in the code example.
<m:Student> <regnum>A108</regnum> <fname>Rob</fname> <lname>Jenkins</lname> <address href="#address1"/> </m:Student>
<m:Student> <regnum>A121</regnum> <fname>William</fname> <lname>Jenkins</lname> <address href="#address1"/> </m:Student>
<m:address id="address1"> <street>11, Oak Street</street> <state>Arkansas</state> </m:address>