XPATH
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Introduction of XPath
XPath is the solution to finding information in an XML document. XPath uses expressions to find elements, attributes, and other information in your XML.
XML documents have a tree structure
- XPath allows you to concisely describe sets of XML elements and attributes in this tree.
- Analogy to file system paths.
- A file system hierarchy is a tree of directories and files.
- A filesystem path describes how to reach a specific file, starting either from the root, or the current working directory.
- XPath exploits this intuitive notion of a path, and extends it to XML documents.
Nodes of XPath
In the XML tree available for XPath expressions, there are 7 node types
- The root node (one per document)
- Element nodes
- Attribute nodes
- Text nodes
- Comment nodes
- Processing instruction nodes
- Namespace nodes
Simple Example
<?xml version="1.0" encoding="ISO-8859-1"?> <bookstore> <book> <title lang="eng">Harry Potter</title> <price>29.99</price> </book> <book> <title lang="eng">Learning XML</title> <price>39.95</price> </book> </bookstore>
Some Expression How to Locate path
| Expression | Description |
| / | 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 current node |
| .. | Selects the parent of the current node |
| @ | Selects attributes |
| Path Expression | Result |
| /bookstore | Selects the root element bookstore |
| 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 |
Advantage of XPath
- Flexible expression- The user may use whatever tags/attributes seem intuitive when designing the schema
- latent semantics- Many users prefer to figure out the semantics when/if necessary
- Application Specific Constraint Checking
- Core Technology- XSLT/XPath is a "core technology" which is well supported, well understood, and with lots of material written on it.
- Expressive Power- XSLT/XPath is a very powerful language. Most, if not every, constraint that you might ever need to express can be expressed using 6.XSLT/XPath. Thus you don't have to learn multiple schema languages to express your additional constraints
- Long Term Support- XSLT/XPath is well supported, and will be around for a long time.
Disadvantage of XPath
- Separate Documents- With this approach you will write your XML Schema document, then you will write a separate XSLT/XPath document to express additional constraints. Keeping the two documents in synch needs to be carefully managed
- Efficiency is access limited
XPATH Tutorials
XPATH Examples
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