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| | | Altova Mailing List Archives>Archive Index >xml-dev Archive Home >Recent entries >Thread Prev - [xml-dev] What is declarative XML? (And what's not) [Thread Next] Re: [xml-dev] What is declarative XML? (And what's not)To: "Costello, Roger L." <costello@-----.---> Date: 6/1/2009 8:57:00 AM [...] The vast majority of XML I work with is RDF/XML. I consider that pretty purely declarative in that it is a carrier notation for simple logical claims. In other words, content that carries logical claims about the world that could (at least ideally) be considered true or false, informative or un-informative... One measure of this is the order-insensitivity of the content (if not the particular syntax in which that content is communicated). I can write RDF/XML that says "Dan works at the Organization with a homepage http://www.vu.nl/, he is 37, his weblog is http://danbri.org/words/". Or I can re-order those 3 claims. RDF tools are pretty oblivious to this ordering, to the extent that users of RDF query languages and APIs can't rely on it being preserved once the XML markup is parsed and handed to RDF layers of processing. This is because there should be no circumstances where the ordering of the claims makes any difference to their overall plausibility. The syntax in which we write those claims in markup might have rules for ordering, however (eg. see rdfa below). I don't want to suggest that RDF is the ultimate in declarative content; there are certainly other traditions and approaches. But being reducable to simple document-order-independent logical claims seems a useful measure of declarativeness (declarativity?). That said, it's hard to quantify. Compare an RDF/XML document and an RDFa/XHTML doc that "said they same thing" from an RDF perspective: <Person xmlns="http://xmlns.com/foaf/0.1/" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <weblog rdf:resource="http://danbri.org/words/"/> <workplaceHomepage rdf:resource="http://www.vu.nl/"/> <age>37</age> </Person> vs <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"> <head><title>RDFa example</title></head> <body><p typeof="foaf:Person">Dan works at the organization with a homepage <a href="http://www.vu.nl/" rel="foaf:workplaceHomepage">www.vu.nl</a>, he is <span property="foaf:age">37</span>, his weblog is <a href="http://danbri.org/words/" rel="foaf:weblog">danbri.org/words</a>.</p> </body> </html> In both cases, if I got my syntax right, the documents are carriers for the same claims about the thing they describe: _:x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://xmlns.com/foaf/0.1/Person> . _:x <http://xmlns.com/foaf/0.1/weblog> <http://danbri.org/words/> . _:x <http://xmlns.com/foaf/0.1/workplaceHomepage> <http://www.vu.nl/> . _:x <http://xmlns.com/foaf/0.1/age> "37" . (rdfa parsers will probably also do something with the title, but forget that for now) Does it make sense to say that either is more declarative? Clearly the XHTML/RDFa carries more information for a human or a full-text indexer, but there is also a sense in which they carry the same machine-oriented payload. Also re thinking about the HTML, RDFa and human-facing document side of this, perhaps also related - some oldish work on XML Accessibility Guidelines - http://www.w3.org/TR/xag cheers, Dan _______________________________________________________________________ XML-DEV is a publicly archived, unmoderated list hosted by OASIS to support XML implementation and development. To minimize spam in the archives, you must subscribe before posting. [Un]Subscribe/change address: http://www.oasis-open.org/mlmanage/ Or unsubscribe: xml-dev-unsubscribe@l... subscribe: xml-dev-subscribe@l... List archive: http://lists.xml.org/archives/xml-dev/ List Guidelines: http://www.oasis-open.org/maillists/guidelines.php | |
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