XPath

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XPath
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XPath

• Used to access part of XML document
• Compact, non-XML syntax
• Use a pattern expression to identify nodes in an
  XML document
• Have a library of standard functions
• W3C Standard

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XPath Example

• Sample XML
• The root element
• /STATES
• The SCODE of all STATE elements of STATES element
  
• /STATES/STATE/SCODE
• All the CAPTIAL element with a CNAME sub-element
  of the STATE element of the STATES element
• /STATES/STATE/CAPITALCNAMEAtlanta
• All CITIES elements in the XML document
• //CITIES

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More XPath Example

• Element AA with two ancestors
• ///AA
• First BB element of AA element
• /AA/BB1
• All the CC elements of the BB elements which has
  an sub-element A with value 3
• /BBA3/CC
• Any elements AA or elements CC of elements BB
• //AA /BB/CC

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Even More XPath Example

• Select all sub-elements of elements BB of
  elements AA
• /BB/AA/
• When you do not know the sub-elements
• Different from /BB/AA
• Select all attributes named aa
• //_at_aa
• Select all CITIES elements with an attribute
  named aa
• //CITIES_at_aa
• Select all CITIES elements with an attribute
  named aa with value 123
• //CITIES_at_aa 123

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Axis

• Context node
• Evaluation of XPath is from left to right
• The context node the current node (set) being
  evaluated
• Axis
• Specifies the relationship of the resulting
  nodes relative to context node
• Example
• /childAA children of AA, abbreviated by /AA
• //AA/ancestorBB BB elements who are ancestor
  of any AA elements

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Axes

• ancestor //BBB/ancestor
•  ltAAAgt           ltBBB/gt           ltCCC/gt
            ltBBB/gt           ltBBB/gt
            ltDDDgt                ltBBB/gt
            lt/DDDgt           ltCCC/gt   lt/AAAgt

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Axes

• ancestor //BBB/ancestorDDD
•  ltAAAgt           ltBBB/gt           ltCCC/gt
            ltBBB/gt           ltBBB/gt
            ltDDDgt                ltBBB/gt
            lt/DDDgt           ltCCC/gt   lt/AAAgt

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Axes

• attribute Contains all attributes of the current
  node
• //BBB/attribute abbreviated by //_at_
• ltAAAgt           ltBBB aa1/gt           ltCCC/gt
            ltBBB aa2 /gt           ltBBB aa3
  /gt           ltDDDgt                ltBBB bb31
  /gt           lt/DDDgt           ltCCC/gt   lt/AAAgt
• //BBB/attributebb

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Axes

• child
• /AAA/DDD/childBBB child can be omitted for
  abbreviation
•  ltAAAgt           ltBBB/gt           ltCCC/gt
            ltBBB/gt           ltBBB/gt
            ltDDDgt                ltBBB/gt
            lt/DDDgt           ltCCC/gt   lt/AAAgt

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Axes

• descendant
• /AAA/descendent
• ltAAAgt           ltBBB/gt           ltCCC/gt
            ltBBB/gt           ltBBB/gt
            ltDDDgt                ltBBB/gt
            lt/DDDgt           ltCCC/gt   lt/AAAgt
• /AAA/descendentCCC ?

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Axes

• parent
• //BBB/parent
• ltAAAgt           ltBBB/gt           ltCCC/gt
            ltBBB/gt           ltBBB/gt
            ltDDDgt                ltBBB/gt
            lt/DDDgt           lt CCC/gt   lt/AAAgt
• //BBB/parentDDD ?

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Axes

• descendant-or-self
• following
• following-sibling
• preceding
• preceding-sibling
• self

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Predicates

• Filters a element set
• A predicate is placed inside square brackets (
  )
• Example //BBBposition() mod 2 0
•    ltAAAgt           ltBBB/gt           ltBBB/gt
            ltBBB/gt           ltBBB/gt
            ltBBB/gt           ltBBB/gt
            ltBBB/gt           ltBBB/gt
            ltCCC/gt           ltCCC/gt
            ltCCC/gt      lt/AAAgt

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Predicates

• //BBB_at_aa31
• ltAAAgt           ltBBB aa1/gt           ltCCC/gt
            ltBBB aa2 /gt           ltBBB aa3
  /gt           ltDDDgt                ltBBB bb31
  /gt           lt/DDDgt           ltCCC/gt   lt/AAAgt
• Is it different from //BBB/attributebb?