The ability to search multiple, incompatible databases is virtually impossible today. XML enables structured data from different sources to be easily combined. This data can then be delivered to clients or other servers for further aggregation, processing, and distribution. The extensibility and flexibility of XML allow it to describe data contained in a wide variety of heterogeneous applications, from describing collections of Web pages to data records. After being delivered to the client, data in XML format can be parsed and locally edited and manipulated, with computations performed by client applications.
Users can manipulate data in various ways, rather than merely presenting it.
Data computations can be performed without additional return trips to the server. Separating the user interface that views data from the data itself allows powerful applications, formerly found only on high-end databases, to be created naturally for the Web using a simple, flexible, open format. Once data has been delivered to the desktop, it can be viewed in different ways. By describing structured data in a simple, open, robust, and extensible manner, XML complements HTML, which is widely used to describe user interfaces. Again, while HTML describes the appearance of data, XML describes data itself.