Friday, 25 February 2005

Well I was talking about XML a while ago...

The article in the Guardian that I quoted from some time ago seemed to say that XML came about from work done on SGML and HTML but that isn't strictly true...

What actually happened was that XML was developed from the same route language as HTML, namely SGML, so it's relationship to the other two languages is more like the illustration below:


+----------------------------------+
| SGML |
+--+-----------------+-------------+
| |
+--+---+ +-----------+-------------+
| | | XML |
| | +-------------------------+
| |
| HTML |
| |
| |
| |
+------+

SGML was used by Tim Berners-Lee as a basis for the development of HTML (HyperText Markup Language) while he worked at CERN and was looking for a way in which scientists working on diverse hardware platforms would be able to share data in a universally accessible format over the infant internet. HTML represents a subset of SGML but it shares only the first feature of SGML - in that it allows the same documents to be read on different systems. It is not formally extensible and it does not enforce specific rules. To some extent it might be said that SGML is the father of both HTML and XML but while HTML represents a subset of SGML, XML represents a simplified version of SGML.