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XPATH

XPATH. Modified Slides from Dr. Sagiv. XPath. A Language for Locating Nodes in XML Documents XPath expressions are written in a syntax that resembles paths in file systems The list of nodes located by an XPath expression is called a Nodelist

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XPATH

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  1. XPATH Modified Slides from Dr. Sagiv

  2. XPath • A Language for Locating Nodes in XML Documents • XPath expressions are written in a syntax that resembles paths in file systems • The list of nodes located by an XPath expression is called a Nodelist • XPath is used in XSL and in XQuery (a query language for XML) • W3Schools has an XPath tutorial • XPath includes • Axis navigation • Conditions • Functions

  3. <?xml version="1.0" encoding="ISO-8859-1"?> <catalog> <cd country="UK"> <title>Dark Side of the Moon</title> <artist>Pink Floyd</artist> <price>10.90</price> </cd> <cd country="UK"> <title>Space Oddity</title> <artist>David Bowie</artist> <price>9.90</price> </cd> <cd country="USA"> <title>Aretha: Lady Soul</title> <artist>Aretha Franklin</artist> <price>9.90</price> </cd> </catalog> An XML document

  4. catalog.xml catalog cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90

  5. The Main Idea in the Syntax of XPath Expressoins • “/” at the beginning of an XPath expression represents the root of the document • “/” between element names represents a parent-child relationship • “//” represents an ancestor-descendent relationship • “@” marks an attribute • “[condition]” specifies a condition

  6. catalog.xml catalog /catalog cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90 Getting the root element of the document

  7. catalog.xml catalog /catalog/cd cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90 Finding child nodes

  8. catalog.xml catalog /catalog/cd/price cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90 Finding descendent nodes

  9. catalog.xml catalog /catalog/cd[price<10] cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90 Condition on elements

  10. catalog.xml /catalog//title catalog //title cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90 // represents any directed path in the document

  11. catalog.xml catalog /catalog/cd/* cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90 * represents any element name in the document

  12. catalog.xml What will the following expressions return? catalog cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90 * represents any element name in the document

  13. catalog.xml /catalog/cd[1] catalog /catalog/cd[last()] cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90 Position based condition

  14. catalog.xml /catalog/cd[@country=“UK”] catalog cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90 @ marks attributes

  15. catalog.xml catalog /catalog/cd/@country cd cd country cd country country USA UK UK title artist price title artist price title artist price Space Oddity Aretha: Lady Soul Dark Side of the Moon David Bowie Aretha Franklin Pink Floyd 9.90 9.90 10.90 @ marks attributes

  16. Relative Navigation Using Axes • Starts with the current node and not with the root (/) • A . marks the current node (e.g., ./title) • A .. marks the parent node (e.g., title/../*) • There are also other axes, e.g., child, descendent, ancestor, parent, following-sibling, etc.

  17. Functions • Many functions that are included in XPath • Some examples: • count() – returns the number of nodes in a nodelist • last() – returns the last node in a nodelist • name() – returns the name of a node • position() – returns the position of the node in the nodelist

  18. Additional Examples ofXPath Expressions These examples use element names that are not necessarily from the XML document that was shown previously

  19. Examples of XPath Expressions • para • Selects the para children elements of the context node • * • Selects all element children of the context node • text() • Selects all text node children of the context node • @name • Selects the name attribute of the context node

  20. More Examples ofXPath Expressions • @* • Selects all the attributes of the context node • para[1] • Selects the first para child of the context node • para[last()] • Selects the last para child of the context node • */para • Selects all para grandchilren of the context node

  21. More Examples ofXPath Expressions • /doc/chapter[5]/section[2] • Selects the second section of the fifth chapter of the doc • chapter//para • Selects the para element descendants of the chapter element children of the context node • //para • Selects all the para descendants of the document root and thus selects all para elements in the same document as the context node

  22. More Examples ofXPath Expressions • //olist/item • Selects all the item elements that have an olist parent and are in the same document as the context node • . • Selects the context node • .//para • Selects the para descendants of the context node • .. • Selects the parent of the context node

  23. More Examples ofXPath Expressions • ../@lang • Selects the lang attribute of the parent of the context node • para[@type=“warning”] • Selects the para children of the context node that have a type attribute with value warning • chapter[title] • Selects the chapter children of the context node that have one or more title children

  24. More Examples ofXPath Expressions • para[@type=“warning”][5] • Selects the fifth para child among the children of the context node that have a type attribute with value warning • para[5][@type=“warning”] • Selects the fifth para child of the context node if that child has a type attribute with value warning

  25. More Examples ofXPath Expressions • chapter[title=“Introduction”] • Selects the chapter children of the context node that have one or more title children with string-value equal to Introduction • employee[@secretary and @assistant] • Selects employee children of the context node that have both a secretary attribute and an assistant attribute

  26. More Examples of Xpath Expressions • /university/department/course • This Xpath expression matches any path that starts at the root, which is a university element, passes through a department element and ends in a course element • ./department/course[@year=2002] • This Xpath expression matches any path that starts at the current element, continues to a child which is a department element and ends at a course element with a year attribute that is equal to 2002

  27. Location Paths • The previous examples are abbreviations of location paths • See XPath tutorial in W3Schools • For example, // is short for /descendant-or-self::node()/. • //para is short for /descendant-or-self::node()/child::para

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