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XML Path Language

XML Path Language. Andy Clark. Overview. Syntax for selecting nodes in an XML document Location paths and expressions Location paths similar to UNIX paths e.g. /usr/local/bin Result of expression can be Set of nodes (“node-set”) Boolean Number String. Location Paths.

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XML Path Language

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  1. XML Path Language Andy Clark 17 Apr 2002

  2. Overview • Syntax for selecting nodes in an XML document • Location paths and expressions • Location paths similar to UNIX paths • e.g. /usr/local/bin • Result of expression can be • Set of nodes (“node-set”) • Boolean • Number • String

  3. Location Paths • Comprised of “steps” • Relative to context node • Each step has three parts • Axis • e.g. parent::, attribute::, child::, descendent::, etc… • Node test • e.g. foo, bar, html:body, etc… • Zero or more predicates • e.g. [1], [foo/bar], [text()=“Andy”], [not(position()=last())], etc…

  4. Axes • Full list • ancestor::, ancestor-or-self:: • attribute:: • child::, descendent::, descendent-or-self:: • following::, following-sibling:: • namespace:: • parent:: • preceding::, preceding-sibling:: • self::

  5. Node Tests • Full list • Name test • e.g. *, qname, etc… • Node type • e.g. node(), text(), etc… • Processing instruction test • e.g. processing-instruction(“xml-stylesheet”)

  6. Predicates • Expressions • Location path • Union of location paths • Variable references • e.g. $name, etc… • String and number literals • e.g. “Andy”, 42, etc… • Functions • e.g. text(), position(), substring(), etc…

  7. Functions • Node-set functions • e.g. position(), last(), local-name(), etc… • String functions • e.g. string(), contains(), substring(), etc… • Boolean functions • e.g. boolean(), not(), etc… • Number functions • e.g. number(), sum(), round(), etc…

  8. Location Path Abbreviated Syntax • Common location paths have short form • self::node() . • parent::node() .. • attribute::bar @bar • child::foo foo • /descendent::foo //foo • descendent::foo .//foo

  9. Path / foo foo/bar foo//bar foo[bar] @baz . .. * @* Selects Root element Element "foo" Child element "bar" of element "foo" Element "bar" descendent of element "foo" Element "foo" contains child "bar" Attribute "baz" This node Parent node Any element Any attribute Basic Examples

  10. More Complex Sample (1 of 2) • Path: • /book/chapter[3]/section[subsection][2] • Selects: • The second section that contains a subsection in the third chapter of the book • In pseudo-SQL: • FROM note root SELECT element “book”, element “chapter” WHERE (position = 3), element “section” WHERE (contains element “subsection” AND position = 2);

  11. More Complex Sample (2 of 2) • Path: • * [ not( preceding-sibling::* [ name() = name( current() ) ] ) ] • Selects: • The set of children elements with unique names • In pseudo-SQL: • FROM node current SELECT element any WHERE ( not( SELECT element any on axis preceding-sibling WHERE (element name = SELECT node current name) ) );

  12. Useful Links • XPath 1.0 Specification • http://www.w3.org/TR/xpath • XSLT 1.0 Specification • http://www.w3.org/TR/xslt

  13. XML Path Language Andy Clark

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