Re: xml-dev Digest 7 Nov 2013 14:35:15 -0000 Issue 2878

[Roger Costello]
>
> It just dawned on me that a "schema validator" is actually a parser.
>
The big "aha moment" for me back in the day was when it dawned on me 
that running Charles Goldfarb's ARCSGML from the command line was 
essentially equivalent to a lex phase, followed by a yacc phase.

Some time later on, when I figured out the SGML Declaration stuff, it 
dawned on me that there was a pre-lex component also, that specified the 
lexical atoms that would then be turned into tokens (the lex-ing) that 
would then be structurally validated (the yacc-ing).

Some time later on, when I figured out OMITTAG and CONREF an CONCUR 
etc., it dawned on me that I could tweak the parsing and validation and 
the resultant parse tree in various ways.

Some time later on, my brain started seeping out of my ears and I began 
wishing that all the various phases had been neatly stacked on top of 
each other as separate pieces of work with some sane stream-centric data 
structure flowing between them. (I think this happened when I was 
reading the HyTime standard.)

Some time later on, my brain fully exploded when I realised that there 
is no clean layered separation possible (at least that I could envisage) 
that would still give you all the features of full-on SGML.

Some time later on, I concluded that this is inevitably true in any 
powerful text processing system because semantics - real semantics - is 
on great big hermeneutic circle.

Sean