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Advanced XPaths

COMP207 Lectures

General Form

XPaths generally take the following form:

/axis1::E1[C1]/axis2::E2[C2]
  • axis are navigation axes.
  • C are conditions.
  • E are name or a tag, attribute or *.
Axis Shorthand Description
attribute @ An attribute
child Default (child:: can be omitted) Any child
descendant //E instead of /descendant::E Any proper descendant
descendant-or-self   Any descendant
ancestor   Any proper ancestor
following-sibling   Any sibling to the right
preceding-sibling   Any sibling to the left
parent .. The parent
self . Yourself

A proper descendant or ancestor is at least one node away (not self).

Conditions

The idea is the if the condition is true, follow the path further.

  • You can use comparitors like =, != and >=.
    • A value can be a relative path expression or any constant.
  • You can combine by using and and or.
//book[category="CS"]/title

You can also write E[i] which is true if the current node is the i-th child of its parent:

//*[category="CS" or category="Scifi"][1]

This would return the first item in “CS” or “Scifi.

You can also use functions like:

  • last()

in place of i.

Boolean Conversions

We can also include additional XPaths and strings in the condition:

  • Returns the titles of all book that have a category:

      //book[category]/title

  • Returns the books if the price attribute is non-empty:

      //book[@price/data()]