<oXygen/> XML Editor User Guide |
XPath is a language for addressing specific parts of an XML document. XPath, like the Document Object Model (DOM), models an XML document as a tree of nodes. An XPath expression is a mechanism for navigating through and selecting nodes from the XML document. An XPath expression is in a way analogous to a Structured Query Language (SQL) query used to select records from a database.
XPath models an XML document as a tree of nodes. There are different types of nodes, including element nodes, attribute nodes and text nodes. XPath defines a way to compute a string-value for each type of node.
XPath defines a library of standard functions for working with strings, numbers and Boolean expressions.
Examples:
child: : * Select all children of the root node.
.//name Select all elements having the name "name", descendants of the current node.
/catalog/cd[price>10.80]Selects all the cd elements that have a price element with a value larger than 10.80
To find out more about XPath, the following URL is recommended: http://www.w3.org/TR/xpath
To use XPath effectively requires at least an understanding of the XPath Core Function Library. If you have this knowledge the <oXygen/> XPath expression field part of the current editor toolbar can be used to aid you in XML document development.
In <oXygen/> a XPath 1.0 or XPath 2.0 expression is typed and executed on the current document from the XPath console available on the toolbar of every open XML document. The results of an XPath query are returned in the Message Panel. Clicking a record in the result list highlights the nodes within the editing panel.
Results are returned in a format that is a valid XPath expression:
- [FileName.xml] /node[value]/node[value]/node[value] -
Example 6.1. XPath Utilization with DocBook DTD
Our example is taken from a DocBook book based on the DocBook XML DTD. The book contains a number of chapters. DocBook defines that chapters as have a <chapter> start tag and matching </chapter> end tag to close the element. To return all the chapter nodes of the book enter //chapter into the XPath expression field, then Enter. This will return all the chapter nodes of the DocBook book, in the Message Panel. If your book has six chapters, their will be six records in the result list. Each record when clicked will locate and highlight the chapter and all sibling nodes contained between the start and end tags of the chapter.
If we used XPath to query for all example nodes contained in the section 2 node of a DocBook XML document we would use the following XPath expression //chapter/sect1/sect2/example. If an example node is found in any section 2 node, a result will be returned to the message panel. For each occurrence of the element node a record will be created in the result list.
In our example an XPath query on the file oxygen.xml
determined that:
- [oxygen.xml] /chapter[1]/sect1[3]/sect2[7]/example[1]
Which means:
In the file oxygen.xml
, first chapter, third
section level 1, seventh section level 2, the example node found is the first in
the section.
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If your project is comprised of a main file with ENTITY references to other files, you can use XPath to return all the name elements of a certain type by querying the main file. The result list will query all referenced files. |
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When the edited document is of type XSL the XPath expression typed in the XPath console is applied over the XML document specified in the transformation scenario associated with the XSL document. <oXygen/> provides a user preference to be set if you want to apply the XPath expression over the XSL document itself. |
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If the document defines a default namespace then <oXygen/> will bind this namespace to the first free prefix from the list: default, default1, default2, etc. For example if the document defines the default namespace xmlns="something" and the prefix default is not associated with a namespace then you can match unprefixed tags in a XPath expression typed in the XPath console by using the prefix default. For example to find all the level elements when the root element defines a default namespace you should execute in the XPath console the expression: //default:level |
To define default mappings between prefixes that can be used in the XPath console and namespace URIs go to the XPath user preferences panel.
To apply a XPath expression relative to the element on which the caret is positioned use the action Ctrl+Alt+.) (also available on the context menu of the main editor panel) to copy the XPath expression of the element to the clipboard and the action of the contextual menu of the XPath console to paste this expression in the console. Then add your relative expression and execute the resulting complete expression.
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