XPath
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XPath XPath Presentation Transcript

  • CIS-189
  •  XPath provides a logical model for working with XML document Nodes are used to represent serialized XML (in memory) ◦ Not all parts of XML document are represented (XML declaration, DOCTYPE) XPath is used in combination with other tools (such as XSLT)
  •  Legal XPath code is called an expression ◦ An XPath expression that return a node set is a location path Expressions can be absolute and relative ◦ Absolute path includes a full definition of how to find node ◦ Relative path is based on current context (location)
  •  Root node represents document ◦ Can have only one child node (document element) Element node represents elements ◦ QName (qualified name) includes namespace prefix and element name Attribute node represent attributes ◦ Have name and value ◦ Are not represented as child nodes Text node represents text value of an element ◦ Does not have a name Namespace node gives access to the namespace URI and prefix Comment node Processing Instruction Node
  •  Boolean ◦ Written as true() and false() String Number – floating point values Node-set – unordered set ◦ Follows document order
  •  Element node references can be spelled out or abbreviated /child::movies/child::movie/child::price OR /movies/movie/price ◦ child::nodename can also be written nodename Attribute node references attribute::attributename OR @attributename
  •  self  following child  following-sibling attribute  namespace ancestor  parent ancestor-or-self  preceding descendant  preceding-sibling descendent-or-self
  •  Default axis Selects nodes that are immediate nodes of context (current) node Can use * to refer to all child nodes
  • <movie> If context is movie<title>Up</title>  Location path<price>4.99</price child::copy (or > copy) returns node<copy>1</copy> set with both copy<copy>2</copy> elements  Location path</movie> child::* (or *) returns node set with title, price, 2 copy nodes
  •  Can use node() to return all child nodes including comments, processing instructions, and text nodes Can return just text nodes using text() ◦ Text nodes are unnamed
  •  Used to select attributes belonging to a particular element node To return all attributes ◦ attribute::* ◦ @* To return particular attribute ◦ attribute::attributename ◦ @attributename
  •  Used to filter node sets ◦ Predicate similar to query criteria Can use specific values or location references
  • XML: Find 3rd Vehicle:<vehicles> /vehicles/vehicle[2] <vehicle model="camaro"> <year>1967</year> (1-based numbering) <engine>327 v8</engine> </vehicle> Find vehicles that are from ‘72: <vehicle model="challenger"> /vehicles/vehicle/[year=‘1972’] <year>1972</year> <engine>383 v8</engine> (return a node set) </vehicle> <vehicle model="baja bug"> <year>multiple</year> <engine>1200 opposing4</engine> </vehicle></vehicles>