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SQL/XML and XQuery: Do we need both?

Although SQL/XML and XQuery are both XML query standards, they are based on quite different models, and fit best in different architectures. SQL/XML fits cleanly into the relational model as a reasonably small extension to traditional SQL. This means that it works well in traditional SQL environments, providing full access to the existing SQL language, including features like updates and full-text queries that are not going to be part of XQuery 1.0. One of the other advantages of using SQL as a basis is that database manufacturers have many years of experience in optimizing SQL queries, which means that many of the optimization issues are well known. Also, it has existing APIs, including ODBC and JDBC. In short, SQL/XML provides the functionality needed for creating XML from relational data while still fitting cleanly into the existing SQL environment. SQL/XML implementations will be available from Oracle and IBM, but not Microsoft, and a cross-database implementation is available from DataDirect Technologies. Oracle's implementation also provides functionality for querying and processing XML as well as SQL, and there is some interest in adding extensions along these lines to SQL/XML. Some members of the SQL/XML task force would also like to see parts of XQuery added to SQL/XML.

XQuery fits more cleanly into the XML environment, providing Native XML Programming for both XML sources and non-XML sources accessed via an XML view. It is well designed for combining data from multiple sources, and is very efficient for a variety of XML programming tasks. However, XQuery is a brand new language - in fact, at the time of writing, XQuery 1.0 is merely a Working Draft, not likely to emerge until the second half of 2004. There is a great deal of enthusiasm surrounding XQuery, most major database vendors have announced support for it, and there is a great deal of research on optimizing XQuery. However, XQuery is a much younger language, the industry has little experience optimizing it, and it lacks some features, including updates and fulltext, that are very important for some kinds of tasks. Also, the API for XQuery, XQuery for Java (JSR 225) is just now being developed.