RE: Potential new issue: PSVI considered harmful

So is it time to quit referring to DTD or schema-spec'd 
languages as "markup application languages" and begin to refer 
them as "markup validation languages"?  If we are going to separate 
defaulting out and say this is an application language 
responsibility, then we just moved it all into the implementation 
of ???  What goes there?

This 

"Instead of saying that the default value for some
attribute is "x", you specify that an application should behave as if
"x" had been specified if no value is supplied"

moves us into the realm of architectural forms.

len


From: Norman Walsh [mailto:Norman.Walsh@Sun.COM]


/ "Simon St.Laurent" <simonstl@simonstl.com> was heard to say:
| I suspect this issue contains at least two architectural sub-issues,
| At 11:13 AM 6/12/2002 -0700, Tim Bray wrote:
|>So I recommend a TAG finding along the following lines:
[...]
|> 2. Type-augmented XML has nothing to say about default values
|> created in any schema.
|
| Should Web architecture reply on explicit values provided directly in
| messages, or rely on outside mechanisms which provide defaults?
|
| I'd much prefer the explicit version, but it's hard to argue against
| defaults after years of HTML practice.

Defaults can be viewed at two levels. At one level, schema validation
augments the resulting infoset to include new information items. This
is typical attribute or element content defaulting.

This kind of defaulting has broader impact than is at first obvious.
It introduces interoperability problems if validation is not always
required and it makes "identity" transformations difficult or
impossible.

I'm inclined to think that this sort of defaulting should be avoided.
At the very least, I think it would make some sense to separate this
from the validation process.

The other way to deal with defaults is to move them up to the
application level. Instead of saying that the default value for some
attribute is "x", you specify that an application should behave as if
"x" had been specified if no value is supplied.

This has disadvantages too, but over time I've come to believe that
they're easier to deal with than the disadvantages of the former.

                                        Be seeing you,
                                          norm

-- 
Norman.Walsh@Sun.COM   | It is not failure of others to appreciate your
XML Standards Engineer | abilities that should trouble you, but rather
XML Technology Center  | your failure to appreciate theirs.--Confucius
Sun Microsystems, Inc. |

Received on Friday, 14 June 2002 15:16:58 UTC