php|architect's Guide to Web Scraping with PHP - Wind Business ...

DOM Extension ” 109
// Returns the first li child node of each ul node
$list = $xpath->query(’//ul/li[1]’);
// Returns all ul nodes containing an li node with the value "foobar"
$list = $xpath->query(’//ul[li = "foobar"]’);
?>
• Square brackets are used to delimit a conditional expression.
• Element and attribute nodes are denoted the same way within a condition as
they are outside of one. That is, elements are simply referred to by element
name and attribute names are prefixed with @.
• The = operator is used for equality comparisons. The converse, the != operator,
checks for inequality. Other fairly standard comparison operators are also
supported, including =.
• A condition comprised only of a single number is actually short for position()
= # where # is the number used. position is a function that returns the position
of each individual node within the current context.
R e s o u r c e s
Only a fraction of what XPath offers has been covered here, mainly basic concepts
and areas that are most likely to be applicable when using XPath to extract data from
retrieved markup documents. Other functions and operators and more advanced
concepts are detailed further in the resources cited at the end of the chapter. Review
of those resources is highly recommended for more extensive and complex data extraction
applications.
• DOM documentation in the PHP manual: http://php.net/dom
• An excellent o v e r v i e w of XML and XPath:
http://schlitt.info/opensource/blog/0704_xpath.html
• M o r e information on XML: http://en.wikibooks.org/wiki/XML:_Managing_Data_Exchange