Re: A28: syntax of markup declarations?
At 09:45 AM 10/8/96 -0700, Tim Bray wrote:
>The question of whether the XML spec should discuss both of these in a
> normative way, and if not, which one, is open and interesting. Your postings
> would lead me to suspect you want to discard validation in the SGML sense,
> and consider a well-formed XML document valid. Which is a reasonable point
> of view, but not mine. At the moment I think that both levels should in fact
> be defined normatively in the XML spec.
I think if we are serious about our design principles, especially the four
"non-negotiable" ones, I should be able to answer my own question (for both
DTD and RE) It wasn't a trick question, Tim, I just decided to check the
3. XML shall be compatible with SGML.
1.Existing SGML tools will be able to read and write XML data.
2.XML instances are SGML documents as they are, without changes to the
instance. 3.For any XML document, a DTD can be generated such that SGML will
produce "the same parse" as would an XML processor.
4.XML should have essentially the same expressive power as SGML.
Note: #1 and #2 describe our goal in its ideal form. If this goal is not
achievable in its fullest form, then we may back out to a weaker form: it
shall be simple to transform XML documents into equivalent SGML documents,
and vice versa. Our intention, however, is to *bite the bullet* and ensure
if we can that no transformation is needed to allow SGML tools to read and
write XML document instances.
#3 and #4 indicate our intentions accurately, but it is not yet clear how
best to formalize and explain the phrase "the same parse", or the phrase
"essentially the same expressive power". These remain open questions; see
point 8 also.
According to those principles, SGML-compatible DTDs cannot be optional. As
much as I would like to make a language where DTDs are totally optional,
I'll have to do it another day. If XML has its own markup declaration
syntax, it must be in addition to an SGML-compatible DTD on every instance.
I think that the first principle that could be construed to support a new
syntax (or my preference, none at all) is #6, XML Documents should be
human-legible and reasonably clear. But #6 isn't in the realm of
"non-negotiable" and it is arguable how much more readable or clear DSD is.
Can we agree that our principles say we should use SGML compatible DTDs? Can
we agree that the principles should still prevail?