XPath and XQuery

Query language for XML

XPath §

• Consists of node (=element) and attribute
• uses and, or for conditionals (not |, &, etc.)
• {xpath}/EMPS/EMP/PHONE[@type] checks for the existence of an attribute
• /bibliography/book/@ISBN returns all attribute values (ISBNs)
• functions:
  • {xquery}x+y,x–y,x*y,x div y,x mod y
  • {xquery}contains(a,b): a contains b
  • {xquery}count($nodeset): number of child nodes in node set
  • {xquery}position(): n-th node
  • Regular Expressions matching {xquery}matches($string, $regex) e.g. {xquery}matches($input, 'H.*o W.*d')
• conditionals:
  • {xquery}x=y note that one equals is fine, {xquery}x!=y
  • {xquery}x>y, {xquery}x < y
  • {xquery}and or not() works. (but &,|,! does not!)
• Access parent node as {xquery}child/.. without trailing backslash
• Accessing Attributes: {xquery}data($person/@name)
• Frequently used in conditions:
  • {xquery}x + y
  • {xquery}x - y
  • {xquery}x * y
  • {xquery}x div y
  • {xquery}x mod y
• functions
  • {xquery}contains(x, y): true if string x contains string y
  • {xquery}count(node-set): counts the number of nodes in node-set
  • {xquery}position(): returns the “context position” (roughly, the position of the current node in the node-set containing it)
  • {xquery}last(): returns the size of the node-set containing the current node
  • {xquery}name(): returns the tag name of the current element
  • {xquery}sum(): returns sum of all matches

XQuery §

Standard format:

<result>{
	for $var in XPATH-QUERY (: Comments :)
	let $var2 ...
	where [condition]
	stable order by,
		$variable ascending,
		$variable descending
	return <elem>{xquery}</elem>
}</result>

Sort §

Conditionals §

Axis Test §

• /: shorthand for child-or-self
• //: shorthand for descendant-or-self
• /..: shorthand for parent
• one of self, attribute,
• parent, child, ancestor,† ancestor-or-self,† descendant, descendant-or-self,
• following, following-sibling, preceding,† preceding-sibling,†
• namespace
• †: These are reverse axes (=produce resulting node-sets in reverse document order)
• Use like:

Existential Conditions (Exists some…) §

Date Operations §

• Dates will be printed as P dD T hH iM sS
  • P just a P.
  • d: Number of Days. D: constant
  • T: constant
  • h: Number of Hours, H: constant
  • i: Number of Minutes, M: is constant
  • s: Number of Seconds S: is constant
• Dates can be
  • subtracted: {xquery}xs:date("1933-06-22") - xs:date("2000-01-01")
  • compared: {xquery}xs:date("1933-06-22") >= xs:date("2000-01-01")

Date functions

year-from-dateTime	day-from-dateTime	minutes-from-dateTime
year-from-date	day-from-date	minutes-from-time
years-from-duration	minutes-from-duration	days-from-duration
month-from-dateTime	hours-from-dateTime	seconds-from-dateTime
month-from-date	hours-from-time	seconds-from-time
months-from-duration	hours-from-duration	seconds-from-duration

Tips and Tricks §

Naming elements using variables: