XPath is a language for defining parts of an XML document. It allows you to locate and operate on elements and attributes using path expressions that work like URLs or file system directories. XPath contains functions for selecting nodes, evaluating expressions, and extracting information from XML documents. It is used by several XML standards and technologies like XSLT, XQuery, XML Schema, and Schematron. The document provides an introduction to XPath basics like selecting elements, using attributes and namespaces, and built-in functions for strings, numbers, and booleans. Additional resources are listed for learning more about XPath.

1. XPath: An IntroductionStuart Myles

2. ObjectivesWhat is XPath?An introduction to the XPath 1.0 languageXML refresherXPath basicsWhat else can you do with XPath 1.0?Where to go for more information

3. XPathXML Path LanguagePath notation with slashesnewsItem/rightsInfo/copyrightHolderrecipe/ingredientList/ingredientLike UNIX directory paths or URLS

4. What is XPath?Syntax for defining parts of an XML documentLocate elements or attributesPerforming operations over dataXPath contains a library of standard functionsNumeric, string, booleanA major part of several XML standardsXSLT, XQuery, XML Schema, Schematron

5. XPath Introduction:XML RefresherXML documents contain one or more elements, delimited by start and end tags<foo></foo>Elements can be nested to any depth<foo> <bar></bar></foo>

6. XML Attributes and Text ContentElements can have attributes<foo lang=“fr”> <bar id=“theOne” lang=“en”></bar></foo>Elements can have text content<foo lang=“fr”> <bar lang=“en”>theOne</bar></foo>Empty elements have no children or text<foo></foo>A shorthand for writing empty elements<foo />

7. XML NamespacesElements can be defined in different namespacesNamespaces look like URLsYou can use xmlns to declare a default namespace<newsItemxmlns='http://iptc.org/std/nar/2006-10-01/'> <itemMeta> <title>Pope Blesses Astronauts</title> </itemMeta></newsItem>newsItemis in the http://iptc.org/std/nar/2006-10-01/namespaceitemMeta and title are also in the http://iptc.org/std/nar/2006-10-01/ nsChild elements inherit from their parents

8. XML Namespace PrefixesYou can use xmlns:prefix to declare a namespace and bind it to a prefix<nar:newsItemxmlns:nar='http://iptc.org/std/nar/2006-10-01/'> <nar:itemMeta> <nar:title>Pope Blesses Astronauts</nar:title> </nar:itemMeta></nar:newsItem>newsItem is in the http://iptc.org/std/nar/2006-10-01/ namespaceitemMeta and title are also in the http://iptc.org/std/nar/2006-10-01/ namespaceTo an XML parser, this document and the previous one are identical

9. XPath Crash CourseThe Basics: Selecting ElementsThe simplest XPath form:one or more tag names, separated by slashes (/)newsItem/itemMeta/title<- title under itemMetaUse * instead of a tag name to match anythingnewsItem/*/title <- title grandchildren of newsItemAn empty tag searches all levels of the tree//title Every title element in the docnewsItem//title Every title under newsItem

10. XPath: Using AttributesAttribute values are indicated by @@rel<- The rel attribute of the current elementElement and Attribute values are tied by /@link/@rel<- The rel attribute of the link elementUse [] for conditional selectionslink[@rel] <- link element with a rel attributelink[@rel = “parent”]link[@size &lt; “1000”]link[not(@href)]

11. XPath and NamespacesXPath supports namespacesnitf:p <- The p element from the nitf namespacexhtml:p <- The p element from the xhtml nsnar:* <- Any element from the nar namespace@atom:* <- Any attribute from the atom nsProtip: if you can’t figure out why your XPathexpression isn’t matching, check the namespace

12. What Else Can XPath Do?Numeric, String, Boolean FunctionsPublication/FilingMetadata[1]Publication/FilingMetadata[last()]Publication/FilingMetadata[last() - 1]FilingMetadata[position() mod 2 = 0]FilingMetadata[Category = “q” or Category = “j”]not(contains(SlugLine, “advisory”))starts-with(FilingOnlineCode, “1”)And XPath 2.0 adds even more functions, including regular expressions

13. More XPath InformationList of examples:http://msdn.microsoft.com/en-us/library/ms256086.aspxIntroductory, interactive tutorial:http://www.zvon.org/comp/r/tut-XPath_1.htmlMore advanced tutorial:http://www.ibm.com/developerworks/xml/tutorials/x-xpath/section2.htmlXPath chapter from XML in a Nutshell:http://oreilly.com/catalog/xmlnut/chapter/ch09.html