MIX: A meta-data indexing system for XML. SungRan Cho, Nick Koudas and Divesh Srivastava. We present a system for efficient meta-data indexed querying of XML documents. Given the diversity of the information available in XML, it is very useful to annotate XML data with a wide variety of meta-data, such as quality and security assessments. We address the meta-data indexing problem of efficiently identifying the XML elements along a location step in an XPath query, that satisfy meta-data range constraints. Our system, named MIX, incorporates query processing on all XPath axes suitably enhanced with meta-data features offering not only query answering but also dynamic maintenance of meta-data levels for XML documents.