If you need to update a website dynamically, the kind of effort you have to put is rigorous. But xml, since it separates data and presentational features of that data, it is easier to update the xml file dynamically and html takes care of how data looks.
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Here is a list of points on why using XML is beneficial
XML data is self-describing. That means it contains both data and information about the data. In records of traditional database systems, before you store data, it requires to define relational schemata, file description tables, external data definitions etc. Where as in xml, these things are not required. Because the data itself contains all these information. Now html is also a markup language. But it only defines how a formatted data is being displayed. In contrary, XML guarantees total usability of data. This is very important for seamless integration of data, as far as business applications are concerned.
XML can be integrated to all the feasible data format like form text and numbers to multimedia like sound, image to active formats like Java Applets or ActiveX Components.
No programming required to modify the presentation of data - You can change the look and feel of documents or even entire websites with XSL Style Sheets without manipulating the data itself
Single source for distributed data - XML documents can consist of data from many different databases distributed over multiple servers. In other words: With XML the entire World Wide Web is transformed into a single all-encompassing database.
Open and extensible - XML’s one-of-a-kind open structure allows you to add other state-of-the-art elements when needed. This means that you can always adapt your system to embrace industry-specific vocabulary.
Future-oriented technology - XML is the endorsed industry standard of the World Wide Web Consortium (W3C) and is supported by all leading software providers. Furthermore, XML is also the standard today in an increasing number of other industries, for example, health care.