THE XML REVOLUTION - TECHNOLOGIES FOR THE FUTURE WEB

Patterns

Patterns are simple XPath expressions evaluating to node-sets.

A given node matches a given pattern if:

the node is member of the result of evaluating the pattern with respect to some context.

Operationally (and intuitively), a pattern matching is probably best evaluated backwards (from right to left).

Recall the structure of XPath node-set expressions:

pattern: location path | ... | location path
location path: /step/ ... // ... /step
step: axis nodetest predicate

a pattern is a set of XPath location paths separated by | (union)
restrictions: only the child (default) and attribute (@) axes are allowed here
extensions: the location paths may start with id(..) or key(..)

A simple example is:

match="section/subsection | appendix//subsection"

which matches subsection elements occurring either as child elements of section elements or as descendants of appendix elements.

These figures illustrate the pattern matching mechanism.

pattern:		location path `\|` ... `\|` location path
location path:		`/`step`/` ... `//` ... `/`step
step:		axis nodetest predicate