be inefficient, and due to the hierarchical nature of XML, custom optimized data structures are used for storage and querying. This usually increases performance both in terms of read-only queries and updates. XML nodes and documents are the fundamental unit of (logical) storage, just as a relational database has fields and rows. The standard for querying XML data per W3C recommendation is XQuery; the latest version is XQuery 3.1. XQuery includes XPath as a sub-language and XML itself is a valid sub-syntax of XQuery. In addition to XPath, some XML databases support XSLT as a method of transforming documents or query results retrieved from the database. Language features Supported APIs Data-centric XML datasets For data-centric XML datasets, the unique and distinct keyword search method, namely, XDMA for XML databases is designed and developed based on dual indexing and mutual summation. References External links Ranking of Native XML DBMS by popularity, updated monthly, from DB-Engines XML Databases - The Business Case, Charles Foster, June 2008 - Talks about the current state of Databases and data persistence, how the current Relational Database model is starting to crack at the seams and gives an insight into a strong alternative for today's requirements. An XML-based Database of Molecular Pathways (2005-06-02) Speed / Performance comparisons of eXist, X-Hive, Sedna and Qizx/open XML Native Database Systems: Review of Sedna, Ozone, NeoCoreXMS 2006 XML Data Stores: Emerging Practices Bhargava, P.; Rajamani, H.; Thaker, S.; Agarwal, A. (2005) XML Enabled Relational Databases, Texas, The University of Texas at Austin. Initiative for XML Databases XML and Databases, Ronald Bourret, September 2005 The State of Native XML Databases, Elliotte Rusty Harold, August 13, 2007 XML Data management Data modeling