XPath(5) Use axis, nodetest and predicate to define path expression

XPath1.0  uses path expressions to select nodes or node-sets in an XML document.

This is the most commonly used technique for xPath. path expression can appear in theselectattribute ortestattribute in the if statement

Syntax:

axis::nodeTest[optional predicate]

example: 
/bookstore/book[position()<3] 
Selects the first two book elements that are children of the bookstore element

axis

There are 13 types of axis:

• child axis - the default axis
• attribute axis - attribute::FName and @FName are equivalent.
• ancestor axis
• ancestor-or-self axis
• descendant axis
• descendant-or-self axis - descendant-or-self::c and a//c are equivalent
• following axis
• following-sibling axis
• namespace axis (not used in XQuery, and deprecated in XPath 2.0)
• parent axis - parent:: and .. are equivalent
• preceding axis
• preceding-sibling axis
• self axis - self:: and . are equivalent

The following picture clarify the relationship of axis

Node Test

Specifies the initial set of nodes.

Could be 

Node Name Test

• * or @*
• QName (qualified name)
• NCName (Named Characters Name) or reqularly named node
• id(id)

Node Type Test

• comment().
• text().
• processing-instruction().
• processing-instruction("target").
• node(). Any node except for attribute nodes and the root node.

Predicate

OPTIONAL, specifies conditions that have to be met by the node among the node set.

CAN BE NESTED axis::nodeTest[optional predicate[optional predicate]]

Can have more than one predicate axis::nodeTest[optional predicate][optional predicate]

Predicates can contain operators and functions!

In fact, predicates can be used to filter any kind of sequence.

More on xPath:

http://www.georgehernandez.com/h/xComputers/XML/XSL/XPath.asp