XPathXML Path Language

1
XPath(XML Path Language)
2
??

• Introduction
• Basics
• Location Paths
• Expressions
• Core Function Library
• Data Model

3
Introduction

• Language for addressing parts of an XML document,
  designed to be used by XSLT and XPointer
• Building blocks for other W3C standards
• W3C Recommendation 16 November 1999
• Version 1.0
• Features
• Address parts of an XML document
• A common syntax and semantics for functionality
• XSLT, XPointer
• Manipulation of strings, numbers, booleans
• Models an XML document as a tree of nodes
• Operate on the abstract, logical structure of an
  XML document
• Fully supports XML Namespace

4
Basics

• Node type for XML document tree
• Root node
• Element node
• Attribute node
• Namespace node
• Processing-instruction node
• Comment node
• Text node

5
Basics

• Expression
• Primary syntactic construct in XPath
• Four basic types
• Node-set
• An unordered collection of nodes without
  duplicates
• Boolean
• True of false
• Number
• Floating-point number
• String
• a sequence of UCS characters

6
Basics

• Context consists of
• a node (context node)
• a pair of non-zero positive integers (context
  position and context size)
• a set of variable bindings
• mappings from variable names to variable values
• a function library
• mappings from function names to functions
• the set of namespace declarations in scope for
  the expression

7
Location Path

• Most important expression in XPath
• Selects a set of nodes relative to the context
  node
• consists of location steps
• location step axis node test optional
  predicate
• Provide syntactic abbreviations
• / document root
• document element? parent

8
Location Path

• Relative location path
• one or more location steps separated by /
• location steps are composed together from left to
  right
• each node in the resulting set of one step
• used as a context node for the following step
• Absolute location path
• / a relative location path (optional)
• Location Step
• Axis Node test Predicates
• ex) child NAME position()5

9
Location Step

• Axes
• specifies the tree relationship between the nodes
  selected by location step and the context node

Ancestor-or-self
Document order
ancestor
ancestor
preceding
following
reverse
parent
following
preceding
self (context node)
following-sibling
Preceding-sibling
forward
child
child
descendant
descendant
Descendant-or-self
10
Node Test

• Specifies the node type and expanded-name of the
  node
• Every axis has principal node type
• Attribute axis attribute
• Namespace axis namespace
• Other axes element
• Node Test
• true for any node of the principal node type
• text() true for any text node
• comment() true for any comment node
• processing-instruction() true for any processing
  instruction
• node() true for any node of any type
• Name true for nodes which has the Name

11
Predicates

• Filters a node-set w.r.t. an axis to produce a
  new node-set
• Expr
• Expr is evaluated for each node to be filtered
• if true, the node is included in the new node-set
• para3 is equivalent to paraposition()3

12
Location Path Examples

• Examples
• /
• selects the document root node
• /descendantpara
• selects all the para elements in the same
  document
• childparaposition()1
• selects the first para child of the context node
• preceding-siblingchapterposition()1
• selects the previous chapter sibling of the
  context node
• childparaattributetypewarningposition()
  5
• selects the 5th para child of the context node
  that has a type attribute with value warning

13
Abbreviated Syntax

• Location Step
• child can be omitted from a location step
• Default axis
• Ex) childdiv/childpara ? div/para
• attribute ? _at_
• Ex) childparaattributetypewarning ?
  para_at_typewarning
• /descendant-or-selfnode()/ ? //
• Ex) /descendant-or-selfnode()/childpara ?
  //para
• selfnode() ? .
• Ex) selfnode()/descendant-or-selfnode()/child
  para ? .//para
• parentnode() ? ..
• Ex) parentnode()/childtitle ? ../title
• //para1 vs /descendantpara1

14
Other Expressions

• Function calls
• FunctionName(Argument1, Argument2, )
• Node-sets
• Location path
• operator
• Computes the union of its operands(node-sets)
• Booleans
• or, and, , !, lt, lt, gt
• lt, lt must be quoted like lt lt in XML
  documents
• Left associative
• 3 gt 2 gt 1 false

15
Expressions

• Numbers
• Floating-point number
• Double-precision 64-bit format
• Nan(Not-a-Number) value
• Positive, negative infinity
• Positive, negative zero
• , -, div, mod
• - operation typically needs to be preceded by
  whitespace
• foo-bar, foo - bar
• Strings
• A sequence of zero or more characters
• A character in XPath
• A single Unicode abstract character
• May be a pair of 16-bit Unicode code values

16
Core Function Library

• XPath implementations must always include
• Node set functions
• number last()
• number position()
• number count(node-set)
• node-set id(object)
• Ex) id(foo)
• string local-name(node-set?)
• string namespace-uri(node-set?)
• string name(node-set?)

17
Core Function Library

• String Functions
• string string(object?)
• string concat(string, string, string)
• boolean starts-with(string, string)
• boolean contains(string, string)
• string substring-before(string, string)
• string substring-after(string, string)
• string substring (string, number, number?)
• number string-length(string?)
• string normalize-space(string?)
• string translate(string, string, string)

18
Core Function Library

• Boolean functions
• boolean boolean(bobject)
• boolean not(boolean)
• boolean true()
• boolean false()
• boolean lang(string)

19
Core Function Library

• Number functions
• number number(object?)
• number sum(node-set)
• number floor(number)
• number ceiling(number)
• number round(number)

20
Data Model

• How XPath models an XML document as a tree?
• Node type
• Root nodes
• Element nodes
• Text nodes
• Attribute nodes
• Namespace nodes
• Processing instruction nodes
• Comment nodes
• string-value
• expanded-name local part namespace URI

21
Data Model

• Root node
• A element node for the document
• Processing instruction, comment nodes for
  children
• string-value
• Concatenation of the string-values of all text
  node descendants
• No expanded-name

22
Data Model

• Element node
• Element, comment processing instruction, text
  node for children
• Has expanded-name
• string-value
• Concatenation of the string-values of all text
  node descendants
• Unique IDs
• Attributes declared in DTD as type ID

23
Data Model

• Attribute node
• Each element node has an associated set of
  attribute nodes
• The element is the parent of each of the
  attribute nodes
• Is not a child of its parent element
• test whether two nodes have the same value
• Not whether they are the same node
• A defaulted attribute is treated the same as a
  specified attribute
• Has expanded-name
• string-value
• Normalized value

24
Data Model

• Namespace node
• Each element has an associated set of namespace
  nodes
• For each distinct namespace prefix in scope for
  the element
• One for the default namespace if in scope for the
  element
• Is not a child of its parent element
• Has expanded-name
• Namespace URI null
• string-value
• Namespace URI

25
Data Model

• Processing instruction node
• For every processing instruction
• string-value
• Part of the processing instruction following the
  target
• Has expanded-name
• Local part processing instructions target
• Namespace URI null
• XML declaration is not a processing instruction

26
Data Model

• Comment node
• string-value
• Content of the comment
• No expanded-name
• Text Nodes
• Character data
• Never have an immediately following/preceding
  sibling text node
• string-value
• Contents
• No expanded-name

27
Reference

• http//www.w3c.org/TR/xpath