THE XML REVOLUTION - TECHNOLOGIES FOR THE FUTURE WEB

Location steps

A single location step has the form

axis :: node-test [ predicate ]

The axis selects a rough set of candidate nodes (e.g. the child nodes of the context node).
The node-test performs an initial filtration of the candidates based on their
- types (chardata node, processing instruction, etc.), or
- names (e.g. element name).
The predicates (zero or more) cause a further, potentially more complex, filtration.
Only candidates for which the predicates evaluate to true are kept.

The candidates that survive the filtration constitute the result.

This structure of location steps makes implementation rather easy and efficient, since the complex predicates are only evaluated on relatively few nodes.

The example from before:

child::section[position()<6] / descendant::cite / attribute::href

selects all href attributes in cite elements in the first 5 sections of an article document.