Tài liệu What Is XQueryX? pptx

Appendix B: What Is XQueryX? One of the most recent developments in the work on XQuery is the efforts of the World Wide Web Consortium (W3C) to specify the XQueryX language. This language enables the full rendering of XQuery in Extensible Markup Language (XML) for computer-readable use and ensures its compliance with W3C requirements. XQueryX is not designed for direct human use. XQueryX is in the very early stages of development. This topic is included to alert you to this emerging technology and to show the rapid pace of innovation with XML. For more information about XQueryX, check the W3C site regularly to monitor the evolution of this probable standard. See the W3C paper XML Syntax for XQuery 1.0 (XQueryX) of June 7, 2001, at http://www.w3.org/XML/Query. XQueryX is needed to make the programmatic use of XQuery consistent with other XML languages and techniques. XQuery in the form you have learned it so far does not appear in true XML format. By using XQueryX, you can turn an XQuery expression into an XML document. If you can represent an XQuery expression in XML through XQueryX, then all other XML techniques for navigation and modification are available to the XML programmer. Introduction Note Why is XQueryX needed? 2 Appendix B: What Is XQueryX? Consider the following FLWR expression from books.xml: FOR $b IN document("books.xml")//book WHERE $b/publisher = "New Moon Books" and $b/year = "1991" RETURN $b/title Converting this to XQueryX produces the following XML document: <q:query xmlns:q="http://www.w3.org/2001/06/xqueryx"> <q:flwr> <q:forAssignment variable="$b"> <q:step axis="SLASHSLASH"> <q:function name="document"> <q:constant datatype="CHARSTRING">books.xml</q:constant> </q:function> <q:identifier>book</q:identifier> </q:step> </q:forAssignment> <q:where> <q:function name="AND"> <q:function name="EQUALS"> <q:step axis="CHILD"> <q:variable>$b</q:variable> <q:identifier>publisher</q:identifier> </q:step> <q:constant datatype="CHARSTRING">New Moon Books</q:constant> </q:function> <q:function name="EQUALS"> <q:step axis="CHILD"> <q:variable>$b</q:variable> <q:identifier>year</q:identifier> </q:step> <q:constant datatype="CHARSTRING">1991</q:constant> </q:function> </q:function> </q:where> <q:step axis="CHILD"> <q:variable>$b</q:variable> <q:identifier>title</q:identifier> </q:step> </q:flwr> </q:query> As you can see, XQueryX is not easy for humans to use, but it is extremely efficient for XML processors. With the extension of XQuery into many areas of Internet and Web activity, such computer-readable and programmer-readable code is essential to the full realization of XQuery’s capabilities. Example . requirements. XQueryX is not designed for direct human use. XQueryX is in the very early stages of development. This topic is included to alert you to this emerging. Appendix B: What Is XQueryX? One of the most recent developments in the work on XQuery is the efforts of the World Wide Web Consortium