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Re: RSS extensibility
On Jan 8, 2005, at 2:21 AM, Danny Ayers wrote:
Perhaps I wasn't clear enough. XML has containment. Individual
specifications may assign it semantics. RDF/XML assigns it semantics
corresponding to the RDF model. Without either the individual
specification's definition, or a generalised interpretation like
RDF/XML's all you have is syntax featuring containment.
No, you were clear, it was just that your statement is false.
Element containment is a semantic that almost all XML data formats obey.
In fact, the only one I know of that doesn't is RDF/XML. No other
format needs to assign those semantics to XML.
But XML containment can only express tree structures. To express graph
structures, the containment must somehow be violated. RDF is a graph.
And Atom feed is a tree. If we try to express tree structures with a
graph language, we create complexity that would not exist with a tree
language because a tree already has constraints built-in. The extra
constraints that RDF needs in order to dig itself out of its own hole
are not necessary for languages that avoid the hole in the first place.
I do hope that folks understand that the relationship should be
obvious to anyone who does not
work in a language that is as perversely non-mark-up as RDF/XML.
Well there you have it - it is possible to design XML languages that
are perverse. So we can't rely on everyone following the 'obvious'
relationship pattern. Making it explicit should help prevent
On the contrary, we can safely ignore languages that are perverse
in their use of XML because those languages will have to define
their own islands of semantics which are self-contained and
irrelevant to their surroundings. Other languages do not have
to understand the non-containment semantics of rdf:Description
because those semantics are defined by RDF/XML regardless of
what other language it may be embedded within.