OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.


Help: OASIS Mailing Lists Help | MarkMail Help



   Re: [xml-dev] The triples datamodel -- was Re: [xml-dev] Semantic Web pe

[ Lists Home | Date Index | Thread Index ]

At 10:52 AM +0200 6/6/04, Henrik Martensson wrote:

>Using the XHTML 1.0 doctype declaration constitutes a promise to stick
>to XHTML, and not to mix in elements and attributes from namespaces
>that have not been declared in the XHTML DTD.

Absolutely not! All using the XHTML DTD promises is that the DTD can 
be found at a certain URL, and used to apply some default attributes 
values and resolve some entity references. It in no way promises that 
the document is valid.

This is one of two qualitative differences between SGML and XML. In 
XML validity is optional. It is *not* required. Adding a document 
type declaration makes no promises that the document is valid. It 
simply says you might find this DTD to be useful when processing the 

Many developers believe that rigid, conservative (everything not 
permitted is forbidden) schemas are necessary to produce software. 
Nothing could be further from the truth. Programming with the 
expectation that the schema will be followed leads to brittle, 
inextensible, closed systems that break at the first whiff of change. 
Robust, flexible software that can handle extensions gracefully 
begins with the realization that any fixed schema is inadequate for 
some uses, and that one must be prepared to handle both schemaless 
and invalid documents.

Again, the question one should ask when presented with an XML 
document is, "Can I extract the information needed to perform my task 
from this document?" The question should not be, "Does this document 
adhere to one very precise and constrained format in the universe of 
all possible formats?"

Sometimes the answer, is "I don't know" and the document may need to 
be kicked to a human for further analysis. In practice, however, most 
systems encounter a fairly limited number of document formats (though 
that limited number is normally greater than 1) and these can all be 
recognized and handled, with occasional fallbacks to people to add 
support for newly recognized formats.

   Elliotte Rusty Harold
   Effective XML (Addison-Wesley, 2003)


News | XML in Industry | Calendar | XML Registry
Marketplace | Resources | MyXML.org | Sponsors | Privacy Statement

Copyright 2001 XML.org. This site is hosted by OASIS