In this article we will learn\u00a0how to use XPath in XSLT. XPath stands for XML Path Language. It is a W3C recommendation. It\u00a0uses ‘path like’ syntax to identify and navigate nodes in an XML document.<\/p>\n
1. Introduction<\/h2>\n
XPath can be used to navigate through elements and attributes in an XML document. XPath contains over 200 built-in functions.\u00a0There are functions for string values, numeric values, booleans, date and time comparison, node manipulation, sequence manipulation, and much more.\u00a0XPath expressions can also be used in JavaScript, Java, XML Schema, PHP, Python, C and C++, and lots of other languages.<\/p>\n
2. Terminologies<\/h2>\n
In this section we will learn about the various terminologies used in XPath.<\/p>\n
2.1 Node<\/h3>\n
In XPath, there are seven kinds of nodes: element, attribute, text, namespace, processing-instruction, comment, and document nodes.\u00a0XML documents are treated as trees of nodes. The topmost element of the tree is called the root element. Look at the following XML document:<\/p>\n
In the above xml person, name, firstName etc are all nodes. ‘persons’ is the root node. Each node has a parent node except the root node.\u00a0Element nodes may have zero, one or more children.\u00a0Nodes that have the same parent are called Siblings. An ancestor is a\u00a0node’s parent, parent’s parent, etc.<\/p>\n
2.2 Attribute<\/h3>\n
Attribute is assigned to the node. In the above example ‘lang’ in an attribute of ‘name’ node.<\/p>\n
2.3 XPath Expressions<\/h3>\n
In general, an XPath expression specifies a pattern that selects a set of XML nodes. XSLT templates then use those patterns when applying transformations. (XPointer, on the other hand, adds mechanisms for defining a point or a range so that XPath expressions can be used for addressing).\u00a0The nodes in an XPath expression refer to more than just elements. They also refer to text and attributes, among other things. In fact, the XPath specification defines an abstract document model that defines seven kinds of nodes:<\/p>\n
\n
Root<\/li>\n
Element<\/li>\n
Text<\/li>\n
Attribute<\/li>\n
Comment<\/li>\n
Processing instruction<\/li>\n
Namespace<\/li>\n<\/ul>\n
The root element of the XML data is modeled by an element node. The XPath root node contains the document’s root element as well as other information relating to the document.<\/p>\n
2.4 XSLT\/XPath Data Model<\/h3>\n
Like the Document Object Model (DOM), the XSLT\/XPath data model consists of a tree containing a variety of nodes. Under any given element node, there are text nodes, attribute nodes, element nodes, comment nodes, and processing instruction nodes.<\/p>\n
In this abstract model, syntactic distinctions disappear, and you are left with a normalized view of the data. In a text node, for example, it makes no difference whether the text was defined in a CDATA section or whether it included entity references. The text node will consist of normalized data, as it exists after all parsing is complete. So the text will contain a < character, whether or not an entity reference such as < or a CDATA section was used to include it. (Similarly, the text will contain an & character, whether it was delivered using & or it was in a CDATA section).<\/p>\n
3. XPath Nodes Selection<\/h2>\n
XPath uses path expressions to select nodes in an XML document. The node is selected by following a path or steps. The most useful path expressions are listed below:<\/p>\n
\n\n
\n
Expression<\/strong><\/td>\n
Description<\/strong><\/td>\n<\/tr>\n
\n
nodename<\/em><\/td>\n
Selects all nodes with the name “nodename<\/em>“<\/td>\n<\/tr>\n
\n
\/<\/td>\n
Selects from the root node<\/td>\n<\/tr>\n
\n
\/\/<\/td>\n
Selects nodes in the document from the current node that match the selection no matter where they are<\/td>\n<\/tr>\n
\n
.<\/td>\n
Selects the current node<\/td>\n<\/tr>\n
\n
..<\/td>\n
Selects the parent of the current node<\/td>\n<\/tr>\n
Below we show the result if we used these XPath expressions on out sample xml:<\/p>\n
\n\n
\n
Path Expression<\/strong><\/td>\n
Result<\/strong><\/td>\n<\/tr>\n
\n
person<\/td>\n
Selects all nodes with the name “person”<\/td>\n<\/tr>\n
\n
\/persons<\/td>\n
Selects the root element persons<\/p>\n
Note:<\/strong>\u00a0If the path starts with a slash ( \/ ) it always represents an absolute path to an element!<\/td>\n<\/tr>\n
\n
person\/name<\/td>\n
Selects all name elements that are children of person<\/td>\n<\/tr>\n
\n
\/\/name<\/td>\n
Selects all name elements no matter where they are in the document<\/td>\n<\/tr>\n
\n
person\/\/name<\/td>\n
Selects all name elements that are descendant of the person element, no matter where they are under the person element<\/td>\n<\/tr>\n
\n
\/\/@lang<\/td>\n
Selects all attributes that are named lang<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
3.1 Predicates<\/h3>\n
Predicates are used to find a specific node or a node that contains a specific value.\u00a0Predicates are always embedded in square brackets.
<\/div> <\/div><\/p>\n
\/persons\/person[1]<\/code> => Selects the first person\u00a0element that is the child of the persons element.<\/p>\n
\/persons\/person[last()]<\/code> => Selects the last person element that is the child of the persons element.<\/p>\n
\/persons\/person[last()-1]<\/code> => Selects the last but one person element that is the child of the persons element.<\/p>\n
\/persons\/person[position()<3]<\/code> => Selects the first two person elements that are children of the persons element.<\/p>\n
\/\/name[@lang]<\/code> => Selects all the name elements that have an attribute named lang.<\/p>\n
\/\/name[@lang='en']<\/code> => Selects all the name elements that have a “lang” attribute with a value of “en”.<\/p>\n
\/persons\/person[age>40]<\/code> => Selects all the person elements of the persons element that have an age element with a value greater than 40.<\/p>\n
\/persons\/person[age>40]\/name<\/code> => Selects all the name elements of the person elements of the persons element that have an age element with a value greater than 40.<\/p>\n
3.2 Selecting Unknown nodes<\/h3>\n
XPath wildcards can be used to select unknown XML nodes.<\/p>\n
*<\/code> => Matches any element node \n@*<\/code> => Matches any attribute node \nnode()<\/code> => Matches any node of any kind<\/p>\n
Below we will apply these on our sample xml<\/p>\n
\/persons\/*<\/code> => Selects all the child element nodes of the persons element \n\/\/*<\/code> => Selects all elements in the document \n\/\/name[@*]<\/code> => Selects all name elements which have at least one attribute of any kind<\/p>\n
By using the | operator in an XPath expression you can select several paths.<\/p>\n
4. XSLT<\/h2>\n
XSLT stands for XSL (EXtensible Stylesheet Language) Transformations.\u00a0XSLT is a language for transforming XML documents.\u00a0XSLT is used to transform an XML document into another XML document, or another type of document that is recognized by a browser, like HTML and XHTML. Normally XSLT does this by transforming each XML element into an (X)HTML element.\u00a0With XSLT you can add\/remove elements and attributes to or from the output file. You can also rearrange and sort elements, perform tests and make decisions about which elements to hide and display, and a lot more.<\/p>\n
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