XML, or extensible markup language, is a meta language, which has certain advantages over HTML (hyper-text markup language).

It allows one to create one's own language with custom tags and rules to dictate how tags should be used. It adds structure and intelligence to the data.

Even if the documents are large in number, a case where it becomes difficult in HTML to conduct an effective search, XML separates display semantics from raw data and allows for creating one set of documents and transforms them for display on variety of devices including mobile phones.

With XML, one can also exchange data between distinct data sources and communicate with heterogeneous applications. But a lot of developers do not like XML as it is verbose due to self-description and because of its platform independence.

If we look at companies who are using XML at present, they are B2B e-commerce companies. One classic example is that of the `What's Related' button on the Netscape Communicator, which gets you a lot of URLs closely related to what you are surfing. When a user places an order, it gets picked up by Java Sevelet or a CGI application, which then directs it to an XML server. The XML server talks to the RBMS server and looks for details.

If the details are not available, it gets directed to other merchants provided they use the same XML format. Standardisation is a major issue in acceptance of XML.