XPath/Basic Syntax

Basic XPath Syntax Expressions that start with a forward slash "/" are called absolute expressions. They start at the root of the document. All other expressions are relative to the current position within an XML document. Expressions are created by creating a list of step expressions of the form step[predicate]/step[predicate]/step[predicate] You can think of the predicate as a filter or conditional expression that service like a WHERE clause in SQL. Sample XML file Many of the examples use a "books" example such as the following: http://raw.github.com/dmccreary/learn-xquery/master/data/books.xml In general the books file has the following structure: <books> <book> <title>XQuery</title> <format>wikibook</format> </book> </books> Basic XPath Expressions The root document node / Note that the forward slash returns the document root, not the full books element. The root node that contains all the books: /books All book elements: /books/book //book The first version is with an absolute path. The second uses a relative path - book elements at any level of the file. Note that the first expression is faster in unindexed XML but within indexed native XML databases the second is faster. A count of the number of books: count(//book) All the book titles: //book/title The second book in the collection: //book[2] The title of the second book: //book[2]/title The third author of the second book //book[2]/author[3] All books with the format "wikibook": //book[format='wikibook'] Get a list of all the publishers //publisher Get a distinct list of the publishers (duplicates removed) distinct-values(//publisher) Books that have at least one price over 30 //book[list-price > 30] XPath abbreviations . represents the current node .. represents the nearest parent node @ represents the attribute delimiter $ represents the variable delimiter [n] represents the n-th child of the current node ancestor::div represents the set of parent div nodes normalize-space(firstname)="Paul" matches Paul regardless of whitespace delimiters boolean(string($myvar) ) checks for empty strings / represents the absolute path of the root node @* represents all attributes of the current node -Return all values using a union of attributes, node names, and text values: @*|node()|text() -Return all of a node's siblings using a union of the preceding-sibling and following-sibling axes: preceding-sibling::node() | following-sibling::node() -Return the adjacent sibling of a specific type //div/following-sibling::h3 -Check string value of current node [. = "Matthew Bob"] -Node identity can be checked using the count() function to see if the intersection of two node-sets of the same length equals the length of either of the node sets(or in the case of a single node set whether it is equal to 1). For example, the following query returns TRUE in this case because both nodes are the same: count(/bk:books | /bk:books/bk:book[1]/parent::*) = 1