Week 3 - XPATH

Table of content

• Review Week2 Tutorial
• Look at some aspects of XML
• Namespaces
• Data Models
• Introduce XPath
• Look at some common XPath syntax

Namespaces

• Allow us to group elements and attributes under a common heading.
• Namespaces are not parts of the XML specifications, but they are widely supported.

Namespaces Declarations

<outerElement xmlns:events="URL" xmlns:graphics="URL">

• You can now use 'events' and 'graphics' prefixes:

<events:title>Content</events:title>

and

<graphics:title>Content</graphics:title>

• URL example: https://www.cdut.edu.cn/nm/week3

Namespaces Types

Default	Explicit
- No prefix - Namespace applies to every unqualified tag (a tag without a prefix).	- Utilizes a prefix. - Shorthand notation for the namespace.

DOM

• Document Object Model (DOM):
  • Originally developed for HTML. Supported by most browsers.
  • Represents the content of the XML or HTML document as a tree structure.
  • Using DOM, we can easily read and update the contents of the document.

• Online DOM viewer: https://software.hixie.ch/utilities/js/live-dom-viewer/

XPATH

• What is Xpath?
  • Allows us to use path expressions to navigate an XML document.
  • It allows us to select only the nodes we're interested in.
• So its:
  • Expression language.
  • Contains some standard functions.
  • Non-XML.
• XSLT relies heavily on the use of XPath to navigate a document, and find relevant nodes.

XPATH Tree Structure

• Xpath works on the following kinds of nodes

TIP

sibling: <正式>兄弟姐妹

Using XPATH

• Xpath works on the following kinds of nodes

Xpath paths (Absolute vs Relative)

Absolute Location Path	Relative Location Path
- If your location path starts with the root node or a forward slash (/) you are using an absolute location path - e.g. /bookstore/book[2]/author	- If your location path begins with the name of a descendant, you're using a relative location path. - Less complex than the absolute path. - e.g. //*/book[2]/author

Xpath tools online

• https://www.easycodeforall.com/generate-xpath.html
• http://xpather.com/

Preparing Notpad++

Some key XPath expressions

• Xpath works on the following kinds of nodes

Expression	Description
nodename	Selects all nodes with the name "nodename"
/	Selects from the root node
//	Selects nodes in the document from the current node that match the selection no matter where they are
.	Selects the value of the current node
..	Selects the parent of the current node
@	Selects attributes

NOTE

* 也作通配符，但会把所有元素一个一个地单列输出

XPath Examples

Path Expression	Result
bookstore	Selects all nodes with the name "bookstore"
/bookstore	Selects the root element bookstore **Note:**If the path starts with a slash ( / ) it always represents an absolute path to an element!
bookstore/book	Selects all book elements that are children of bookstore
//book	Selects all book elements no matter where they are in the document
bookstore//book	Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element
//@lang	Selects all attributes that are named lang

Namespaces Xpath Examples

Predicates

Predicates examples

Path Expression	Result
/bookstore/book[1]	Selects the first book element that is the child of the bookstore element.
/bookstore/book[last()]	Selects the last book element that is the child of the bookstore element
/bookstore/book[last()-1]	Selects the last but one book element that is the child of the bookstore element
/bookstore/book[position()❤️]	Selects the first two book elements that are children of the bookstore element
//title[@lang]	Selects all the title elements that have an attribute named lang
//title[@lang='en']	Selects all the title elements that have a "lang" attribute with a value of "en"
/bookstore/book[price>35.00]	Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00
/bookstore/book[price>35.00]/title	Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00

Other Examples:
//Actor [@gender='male’]
//Movie[2]/Top_Cast/Actor[@gender='male’]
//Movie[2]/Top_Cast/Actor[last()]/.
//Actress[text()='Takayo Fischer’]
/Movies/Movie[2]/Top_Cast/Actress [@gender='female'][last()-1]

XPATH Axes

• An Axes represents a relationship to the current node on the tree.

AxisName	Result
ancestor	Selects all ancestors (parent, grandparent, etc.) of the current node
ancestor-or-self	Selects all ancestors (parent, grandparent, etc.) of the current node and the current node itself
attribute	Selects all attributes of the current node
child	Selects all children of the current node
descendant	Selects all descendants (children, grandchildren, etc.) of the current node
descendant-or-self	Selects all descendants (children, grandchildren, etc.) of the current node and the current node itself
following	Selects everything in the document after the closing tag of the current node
following-sibling	Selects all siblings after the current node
namespace	Selects all namespace nodes of the current node
parent	Selects the parent of the current node
preceding	Selects all nodes that appear before the current node in the document, except ancestors, attribute nodes and namespace nodes
preceding-sibling	Selects all siblings before the current node
self	Selects the current node

XPATH Axes Examples

AxisName	Example
ancestor	//Actor/ancestor:😗
ancestor-or-self	//Actor/ancestor-or-self:😗
attribute	//Actor/attribute::gender
child	//Top_Cast/child::Actor[text()='Will Smith’] //Movie/child:😗
descendant	//Movie/descendant:😗
following-sibling	//Actor [text()='Will Smith']/following-sibling::Actress
parent	//Actor [text()='Will Smith']/parent:😗
self	//Actor/self:😗