<xsl:attribute name="mergekey">
<xsl:text>title </xsl:text>
<xsl:value-of select="marc:datafield[@tag='245']/marc:subfield[@code='a']"/>
- <xsl:value-of select="marc:datafield[@tag='245']/marc:subfield[@code='b']"/>
<xsl:text> author </xsl:text>
<xsl:value-of select="marc:datafield[@tag='100']/marc:subfield[@code='a']"/>
</xsl:attribute>