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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.


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