w3.org provides a page, where they try to explain XML in ten points.
Nice icons illustrate the points like this one adding structure into data by using XML
...XML is a set of rules for designing text formats that let you structure your data. XML is not a programming language, and you don't have to be a programmer to use it or learn it. XML makes it easy for a computer to generate data, read data, and ensure that the data structure is unambiguous. XML avoids common pitfalls in language design: it is extensible, platform-independent, and it supports internationalization and localization...
It is a really nice introduction for all, who are not so familiar with programming. I think, they should add an eleventh point:
XML is today the key point for data exchange in the world of service orientation and it is the base for WSDL, BPEL and other languages, which will influence the evolution of IT for the next ten years.
Oracle has integrated native XML handling into their Application Server 10g. There is an XML developement kit with the following key features available:
XML 1.0 (Second Edition)
DOM Level 2.0 Specification
DOM Level 3.0 Specification
SAX 2.0 & SAX Extensions
XSLT/XPath 1.0 Specifications
XSLT/XPath 2.0 Specifications
XML Schema Specifications
If you download the XDK, there are many demos included. I liked the XSLSample.java which you can invoke with two command line arguments. First one is the XSLT, the second one is the XML. With this example you can easily verify XSLTs and on the other hand you can learn how to write Java code to do it...
The SOA Suite uses this XDK for all XML processing. For all details take a look at this page. Examples are provided here.
I think everyone should be familiar with details of SAX/DOM (or XSLT or XPATH or...) and should know how it could be coded in Java or C.
Ten years after the specifiation of XML it is very well supported on all platforms and programming languages. Many generators are provided to help the programmers for their daily work with XML.
Let's see where we going in the next ten years....