I am having trouble trying to implement parameter entities so that i can repeat text multiple times within the DTD.

example XML code:
<accounts>
<luke>
<shipping_address>
<address></address>
<street></street>
<city></city>
<postcode></postcode>
</shipping_address>
</luke>

<angie>
<billing_address>
<address></address>
<street></street>
<city></city>
<postcode></postcode>
</billing_address>
</angie>
</accounts>

The address, street, city, postcode elements both have the same information. How would i reuse these sets of elements multiple times within a DTD document using parameter entity ? i know the key syntax is the % sign, but i can't seem to understand how to code it properly.