On 03-May-01 MJ Ray wrote:
Steve Fosdick fozzy@pelvoux.demon.co.uk writes:
[...] What I have more trouble understanding is how XML differs from SGML.
XML is SGML-- rather than HTML++. It's just a bit simplified and easier to parse, I believe. The stylesheeting for XML (XSLT) is also supposedly easier to implement than for SGML (DSSSL), but that seems to be a matter of infrequent argument, as XSLT is Java-orientated while DSSSL is lisp-family-focused. -- MJR
I agree with the statement that XML is SGML but easier to pass. SGML is a standardised version of GML which was a well done solution to the problem of how do we write a good type setting system.
What IBM did was it went out to speak to type setters and find out about the way type setting was done (specificly french type setters, please correct me if you know better) they then simplified the short hand layoutr system.
Essentially content providers labeld their content with <TAGS> and then the documents where passed on to page layout guys who added yet more tags, and finnally out to the guys wqwho made out the pages using the tags to build the page almost like a computer.
This waqs of cause being human full of exceptions and non standard bits, that IBM stripped out. They did not go so far as to lose all of this after all bytes costed in thoughs days. So SGML standardised this legacy system, which was a bit complex.
XML was just an attempt to rationalise this proses for the internet as no one used SGML for the internet as SGML people initially thought they would think thier skills would be good so they gave it another go and also their was a lot of little bits to SGML that could be lost with no hastle to any one and increase the speeed of the software and reduce the time taken to learn your way arround.
I would disagree though that XSL is like java, rather more like prolog meets a procedural language with SQL like libarys. SGML for me became instantly dated and of nothing more than historical interest after I had a look at it. as for DSSL i have not a clue.
Owen Synge