Is it possible to have a Global variable kind of concept which can
be set to different values in the program based on conditions & used???

Why not? You can implement any logic in order to compute variable value, e.g.
<xsl:variable name="var">
	<xsl:choose>
		<xsl:when test="A/B > 0">1</xsl:when>
		<xsl:otherwise>0</xsl:otherwise>
	</xsl:choose>
</xsl:variable>

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Oleg Tkachenko
Multiconn International, Israel