xPath

Definition

XPath

W3C standard: query language for XML

Documents as tree with 7 kinds of nodes:

- Document node - Element node - Attribute node - Text node - Namespace node - Processing-instruction node - Comment node

Location Paths

Location Path

location steps to a node, each seperated by / :

axis :: node_test [predicate-1] [predicate-2] ...

axis relationship

node_test type of node

predicate filter (can be 0 or more)

Axis

Unless specified, we always select nodes and not attributes, namespaces.

self selects origin

attribute selects attributes for that element (but not the defined namespace)

namespace selects namespace defined for that element

child selects all children

descendant selects all decendants

descendant-or-self selects all decendants and self

parent selects parent (can only be a single node in tree)

ancestor selects all ancestors

ancestor-or-self selects all ancestors and self

following selects all following (= below the element in the XML document)

following-sibling selects all following but without their children and grandchildren ...

preceding reverse of “following” (= above the element in the XML document)

preceding-sibling reverse of “following-sibling” (no grandchildren ...)

Node-Test

::node() selects all nodes independent of axis

::name selects nodes with the “ name ”, based on axis

::text() selects text

::* selects all nodes based on axis

Predicate

Predicates are XPath expressions and they filter initial list of nodes (applied from left to right).

General XPath expressions

Location paths $\subset$ XPath expressions

Location paths return: node sets

XPath expressions return: number, string, boolean, node-sets

XPath operators

Syntactic Sugar

Syntactic sugar (Abbreviated Syntax) for shorter expressions.

/descendant-or-self::node()///

self::node().

parent::node()..

child::nothing

attribute::@

position() = nn

Examples of usage

/child::courses/child::course[attribute::semester]
/courses/child::course[attribute::semester]
/courses/course[attribute::semester]
/courses/course[@semester]

/child::courses/child::course[position() = 1][attribute::semester = "Summer"]
/courses/child::course[position() = 1][attribute::semester = "Summer"]
/courses/course[position() = 1][attribute::semester = "Summer"]
/courses/course[1][attribute::semester = "Summer"]
/courses/course[1][@semester = "Summer"]

/descendant-or-self::node()/child::course[position() = 1][attribute::semester = "Summer"]
//child::course[position() = 1][attribute::semester = "Summer"]
//course[position() = 1][attribute::semester = "Summer"]
//course[1][attribute::semester = "Summer"]
//course[1][@semester = "Summer"]

(all equivalent)