RE: Why Are Schemas Hard? (WAS RE: "Uh, what do I need this for" (wasRE: XML.COM: How I Learne d t o Love daBomb))

[Jeff Lowery <jlowery@scenicsoft.com>]

> > 1.  What about Schemas is hard?

To me, it boils down to whether they're conceptually hard or syntactically
hard. If it's the later, then tools will mask the syntax difficulties. It
seems the WG went beyond well-formedness and strived to remove any implicit
assumptions, for example:

<element name="foo">
	<complexType>
		<sequence>
			<element name="bar" type="string"/>
			<element name="baz" type="integer"/>
		</sequence>
		<attribute name="qux" type="decimal"/>
	</complexType>
</element>

Now, couldn't this have been simple stated as:

<element name="foo">
	<element name="bar" type="string"/>
	<element name="baz" type="integer"/>
	<attribute name="qux" type="decimal"/>
</element>

where there's an implicit complexType and sequence? I'm sure this would not
appeal to a lot of people, so especially those driven nuts by the
ambiguities of HTML, but it sure would have made the syntax less verbose. 

But it really doesn't matter, much, IMHO. Tools will cover this annoying
verbosity in any case. The parser will be simpler which is probably more
important.

If Schemas are conceptually hard, that's a different matter. certainly the
rules for namespaces, <all> model groups, and seemingly odd inheritance
restrictions certainly are difficult to master. Here, tools may help by
enforcing these rules through edit controls and choice presentation, but
that's not sufficient for understanding by the schema author. To understand,
he needs not only to know the spec (which is no easy task), but the
decisions and compromises that were made in the writing of the
Recommendation. 

This is where XSDL will stand or fall, on the conceptual complexities, not
the syntactical ones. And I don't think those concepts and their motivations
are forthcoming in an easily digestible way for Schema authors. You'd have
to be a WG member who took good notes to do this, and you have to speak
plain. Not easy for most experts.