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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Namespaces hate validation!
At 05:15 AM 1/6/99 -0500, Ronald Bourret wrote:
>Murray Maloney wrote:
>
>> At 08:46 PM 1/5/99 -0500, Tim Bray wrote:
>>
>I think what Tim is saying is that it is non-trivial to automagically
>combine DTDs or in some sense to say that a given document validates
>against two or more different DTDs. As XML currently stands, this seems to
>be possible only through the liberal use of ANY in content models, which is
>a less-than-optimal solution.
Easy enough to write a DTD that matches an instance. Just inspect
the instance and generate a DTD that captures its models.
The trick is to be able to write a DTD that encompasses
a class of documents that might be validated by it.
As I see it, Tim's algorithm is useful only if you are
willing to write a new DTD for almost every document you get.
>
>(I assume that the Contents=Open/Closed property in DCD is intended to
>address this further. When an element is declared as having open contents,
>it can contain child elements that are not declared in its content model.
> In other words, it allows schema designers to explicitly state where the
>content model can be altered/expanded. This is the same as ANY except
>#PCDATA is not allowed unless it was in the original content model. A
>further refinement would be to say that Contents=Open means that elements
>not declared in the current schema can occur as children. This would meet
>the needs of schema merging without allowing people to "violate" the cur
>rent schema.)
Right. Well, content="open" tries to merge well-formedness
with limited-validity. If that were an acceptable threshold
for validity, then XML should have incorporated it.
>
>> >5. You preprocess the DTD, rewriting all the element & attribute
>> > declarations with the appropriate prefixes
>>
>> Using special care to take into account the non-XML notion
>> of "global attributes".
>
>I don't understand this comment. Global attributes don't currently exist
>in XML, so how can a DTD even contain them? This comment makes sense only
>if you are using a schema language that supports global attributes, which
>doesn't apply in the case the algorithm addresses.
Sorry, I was being facetious.
Global attributes exist in "Namespaces in XML" but not in XML itself.
Curious, no? My point is that "global attributes" as described in
"Namespaces in XML" are a crock -- because there is no such thing as
a global attribute "in XML".
>> >6. You preprocess the instance, making all namespace prefixes
>> > explicit (no defaulting), declaring all the namespaces on the root
>> > element, and using the same set of prefixes you used in the DTD
[...]
>If you are stating that the algorithm doesn't work, it does: Prefixes are
>mapped first to URIs, then to unique prefixes. Therefore, it doesn't
>matter if a prefix is reused in an instance -- at any given point in time,
>it maps to a unique URI, and thus to a unique prefix.
Please re-read what Tim said: "...declaring all the namespaces on
the root element"
This assumes that all prefixes are unique. One cannot make such
an assumption. Hence, this aspect at least does not work.
>> > Well, tedious enough to make it unlikely that anyone will use
>> > validation on documents that utilize namespaces. It is hard.
>> > It is too hard. And for that reason, among others, Veo has
>> > vociferously opposed "Namespaces in XML".
>
>This might be true, although it is easy enough to write a tool that did the
>preprocessing necessary for this to work with the current batch of parsers.
> In the long run, these questions disappear anyway, as the current schema
>proposals can declare which namespace a given element or attribute belongs
>to, thus solving the problem of no namespace declarations in the DTD.
I dispute "easy enough". If that is true, then please show evidence.
If someone would just send me the URL where I can find the listing
of tools that automagically rewrites namespace-aware XML DTDs for me,
then I will reconsider my opinion. :-{
I assert that those of us who consider such a tool easy to create
are the ones who are least likely to actually write the tool.
>
>> As a co-author of one of the schema submissions, I have to say
>> that I do not see how to integrate "Namespaces in XML" -- as
>> it is currently proposed -- with an XML Schema language. Perhaps
>> someone will show me the error of my ways in the fullness of time,
>> but I am skeptical.
>
>XSchema already does this.
Well, I just looked at XSchema again, and while it does include
some facilities for namespace-awareness, it is not clear to me
that it integrates "Namespaces in XML".
In a fact, I have to challenge your assertion that XSchema
integrates with "Namespaces in XML". Quoting from XSchema (4.3.2):
The following XSchema structures cannot be converted
to DTD structures because such structures do not exist:
- More elements, AttDef and AttGroup elements that do not
apply to a particular element, and Model and Enumeration
elements nested directly beneath an XSchema element.
- All id attributes, all attributes of the XSchema element
except for prefix, all ns and ElementNS attributes, and
the Root attribute of the ElementDecl element.
- Nesting of schema information provided by nested XSchema
elements.
------------
Please note that SOX also incorporates a namespace facility
which encompasses elements, attributes, notations, entities,
and processing instructions. Thus, it is not compatible with
the "Namespaces in XML" proposal.
>
>DCD almost does this, but is silent on how it associates namespace prefixes
>used in attribute values (such as the name of an element being declared)
>with URIs.
[...]
So, DCD does not integrate with "Namespaces in XML".
>In any case, it is certainly possible to integrate the current namespace
>proposal with a schema language, as XSchema shows.
XSchema shows no such thing as section 4.3.2 makes clear.
Regards,
Murray
Murray Maloney, Esq. Phone: (905) 509-9120
Muzmo Communication Inc. Fax: (905) 509-8637
671 Cowan Circle Email: murray@m...
Pickering, Ontario Email: murray@y...
Canada, L1W 3K6
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