XML.com FAQs > A. General questions
Question:  A.12 What is the difference between XML and C or C++?

C and C++ (and other languages like FORTRAN, or Pascal, or BASIC, or Java or dozens more) are programming languages with which you specify calculations, actions, and decisions to be carried out in order:

mod curconfig[if left(date,6) = "01-Apr", t.put "April Fool!", 
    f.put days('31102001','DDMMYYYY')-days(sdate,'DDMMYYYY')
           " shopping days to Samhain"];

XML is a markup specification language with which you can design ways of describing information (text or data), usually for storage, transmission, or processing by a program: it says nothing about what you should do with the data (although your choice of element names may hint at what they are for):

<part num="DA42" models="LS AR DF HG KJ" update="2001-11-22">
  <name>Camshaft end bearing retention circlip</name>
  <image drawing="RR98-dh37" type="SVG" x="476" y="226"/>
  <maker id="RQ778">Ringtown Fasteners Ltd</maker>
  <notes>Angle-nosed insertion tool <tool id="GH25"/> is
  required for the removal and replacement of this item.</notes>

On its own, an SGML or XML file (and HTML) doesn't do anything. It's a data format which just sits there until you run a program which does something with it. See also the question about how to run or execute XML files.

This FAQ is from The XML FAQ, maintained by Peter Flynn