Understanding Advanced XML Concepts

As we know XML is a simple and effective way of describing data and it is independent of underlying hardware and software platforms. With its popularity and increasing usage, the process of continuous enhancements in XML specification is also on the way. Here we will discuss some advanced XML concepts which includes the understanding of XPath, XSLT, XQuery, XLink and XPointer.

Lets start with XPath. It is a major part of XSL specification and allows us to navigate through an XML document. As the name indicates it uses path expressions in order to navigate through the document and to find the required information. It uses predefined standard functions for performing different operations on the XML data like for doing comparison of data or manipulating a data value. In terms of XPath all the elements, attributes, comments or instructions of the XML document are known as nodes and the whole document can viewed as a tree of nodes. The topmost element is called root.

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XSLT is also a part of XSL and stands for XSL Transformations. By virtue of XSLT we can transform XML documents into other formats like HTML or XHTML. These transformations do not alter the original document but create a new one on the basis of the first one. XSLT implementations can be done on the client side if we have a browser supporting the XML parser with the help of JavaScript. If it is not possible then these transformations can be implemented over server and the resulted document would be sent back to the browser for display. XSLT uses XPath for navigation purpose and for finding information related to elements and attributes in the XML document.

Now we will discuss about XQuery which is a mechanism to fulfill the purpose of querying XML data. As we use SQL to query database, in the same way XQuery allow us to query XML documents and XML based databases. XQuery is based on XPath expressions and both use the same set of functions. Also they are based on same data model. So XQuery fulfill the need of data extraction from an XML document or database. XQuery has FLOWR (stands for FOR, LET, WHERE, ORDER BY, RETURN) expressions which allows mixing, manipulation and restructuring of XML data.

Next stuff to discuss is the concept of XLink and XPointer. XLink stands for XML Linking Language and it is a mechanism to create hyperlinks in the XML file. We can design one way or multi directional hyperlinks using XLink. XPointer stands for XML Pointer Language and it allows referring to specific elements or fragments of an XML document. Both of these XML linking and addressing languages are closely related and uses XPath expressions.

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