<dc:identifier id="BookId" opf:scheme="URI">
<xsl:apply-templates select="//dc:identifier.url" />
</dc:identifier>
+ <dc:identifier id="BookId" opf:scheme="ISBN">
+ <xsl:apply-templates select="//dc:source.ISBN" />
+ </dc:identifier>
<dc:subject>
<xsl:apply-templates select="//dc:identifier.url" />
</dc:subject>