How to get an absolute path to the directory of the XSL file?

My Schema.xsd file is located in the same directory with the .xsl file. In the .xsl file I would like to generate a link to Schema.xsl in the generated output. The generated output is located in different directories. Currently I do it like this:

   <xsl:template match="/">
     <root version="1.0" xmlns:xsi="http://ift.tt/ra1lAU"
           xsi:noNamespaceSchemaLocation="../../../Schema.xsd">
     <!-- . . . -->

However this forces the generated output to be located 3 levels under the directory of Schema.xsd. I would like to generate an absolute path to the schema in the output, so the output could be located anywhere.