11.1 Background

• XPath is a query language for for addressing XML-expressed information.
• The language relates to nodes within a DOM tree
• The response of a query is a set of nodes.
• Used by XSLT, XQuery, XPointer, and XML Schema
• A generalization of the notion of path expressions of file systems

  /	root directory; directories concatenation
  .	current directory
  ..	parent directory
  name	specified file/directory	/usr
  ?	wild character	?, ??, ?abc?
  [characters]	a character from the given set--limited form of ‘?’	[a-z]
  *	wild string	/urs/games/*
  {str-1, str-2,...}	a string from the given set--limited form of ‘*’	../urs/bin/a{12,21}*

  /                                  |                               +------+                               |      |                              usr    tmp                               |                           +-------+                           |       |                          bin    games                           |     +-------+---------+--------+--------+------+     |       |         |        |        |      |   javac   java     javadoc   javap     diff   grep

• Applications: ls dir-1/ , mv dir-1/files dir-2