XPath includes the usual Boolean operators, in the form of the keywords "or," "and," and "not." Using our "account-status" nodeset, the following expression could be used to obtain all past-due account status elements with an account number over 25000.
account-status[past-due > 30 and account-number > 25000]
Parenthetic groupings can be combined with logical and arithmetic operators to create more sophisticated expressions. For instance, suppose we have a document "boxes," show below
and want to extract those members with a volume greater than 2000. This can be accomplished using the expression
boxes/box[(length * width * height) > 2000]
Embedding XPath expressions within a filter is allowed; making it possible to filter elements based on any of their descendents, not just their immediate children. Let's enhance our "box" elements to include a "material" child representing the stuff a box is actually made of.
The following expression can then be used to extract all elements representing boxes with a volume greater than 1500 and a thickness less than 10.
The result of evaluating the expression consists of the element boldfaced above.
XPath expressions embedded in filters may themselves includes XPath expressions. Let's say our theoretical set of boxes is allowed to have members for which no material name is specified—that is, they may be made of cardboard, or wood, or whatever—it's unspecified.
If we want to extract only those boxes over a certain thickness for which a material name is specified, the easiest way to do it is with a nested filter (highlighted below).
The two elements matching these criteria are boldfaced in the same nodeset shown above. Note that the last box in the set would have qualified if a material name had been present.
Note: The sample code in this tutorial makes use of the Tectonic programming language
(featured in the Delve SOA Fast-Prototyping Toolkit)
Not sure exactly what the heck XML is? Get started with this
excellent wikipedia article:
> Click Here!
