create XSD for element with same name

Question

how to make xsd for element with same names that only identifyed by attribute value example :-

<a>
<b n="structure one">
<c n="inner element 1"/>
<c n="inner element 2"/>
<c n="inner element 3"/>
</b>
<b n="structure two">
<c n="inner element 1 for structure two"/>
<c n="inner element 2 for structure two"/>
<c n="inner element 3 for structure two"/>
</b>
</a>

notice that from the XML i have to mention specific value that belong to the inner element same for structure