...
<ref>
<element-citation publication-type="database" publication-format="disk">
<name><surname>Walker</surname>
<given-names>MM</given-names></name>
<name><surname>Keith</surname>
<given-names>LH</given-names></name>
<source>EPA&rsquo;s Clean Air Act air toxics database</source>
<comment>[disk]</comment>
<publisher-loc>Boca Raton (FL)</publisher-loc>
<publisher-name>Lewis Publishers</publisher-name>
<date-in-citation content-type="copyright-year"
iso-8601-date="1992">1992-1993</date-in-citation>
<comment>4 computer disks: 3 1/2 in</comment>
</element-citation>
</ref>
...



                  
...
<ref>
<mixed-citation publication-type="database" publication-format="disk">
<string-name><surname>Walker</surname>
<given-names>MM</given-names></string-name>,
<string-name><surname>Keith</surname>
<given-names>LH</given-names></string-name>.
<source>EPA&rsquo;s Clean Air Act air toxics
database</source> [disk]. <publisher-loc>Boca
Raton (FL)</publisher-loc>: <publisher-name>Lewis
Publishers</publisher-name>;
&copy;<date-in-citation content-type="copyright-year"
iso-8601-date="1992">1992-1993</date-in-citation>.
4 computer disks: 3 1/2 in.</mixed-citation>
</ref>
...