Tax? Or Precision?

Recovered from the Wayback Machine.

I read the comments about “RDF tax” and how we must “prove” RDF’s worth, yet when I look at so many plain XML feeds, all I can see is the improvement that could be added because of the precision of using RDF/XML. Not all XML feeds, but any that are purposed beyond being generated and consumed by one product.

For instance, in an IRC conversation yesterday about the Pie/Echo/Atom syndication feed, a question arose about how to interpret the ordering and grouping of the contributors and entries within the plain vanilla XML feed. Yesterday’s exercise was focused on doing a straight port of functionality, which meant, according to the participants, that both the entries and contributors needed to be placed within an RDF Seq container. Why? Because order is implied in XML. Or part of the specs, I’m not sure which.

A discussion then commenced that just because XML enforces a grouping and a sequencing on child elements by some form of default, doesn’t mean we have to constrain the same elements within RDF/XML; we have other options built directly in the syntax. We could use repeating properties, which means there is no implied grouping. We could use a Seq, which means there is a grouping, and a sequence to the elements. Or we could have used a List, which also includes a nil factor, meaning that these elements are in a group, and there are no other members for this group. There’s a lot less ’slop’ built into RDF/XML then there is in just plain XML by default.

That “RDF/XML” tax, as it’s called, opened up a door to a conversation that forced the members of the Pie/Echo/Atom group to look at implicit behavior and XML and decide if this is the type of behavior they want to enforce; or whether this is the type of behavior imposed by tree structure nature of the hierarchy of XML. As Sam wrote:

(T)his effort provided an alternate insight into this data, which surfaced a number of questions I never pondered before. For example: is the order of contributors significant? This needs to be answered and documented.

Of course, we can use XML DTDs and XML Schema and a host of other XML ancillary specifications to provide the same precision as we have within the RDF/XML model and syntax; but it doesn’t strike me that the vanilla XML is all that ‘readable’ at this point. In fact, seems to me that you’d have to spend at least as much time reading and working with the XML specifications to do XML ‘properly’ as you would with RDF/XML.

In other words, there’s a ‘tax’ to XML, too, but it can be ignored if you don’t care whether your feed is imprecise. In fact, if my memory serves me, one of the reasons why people had trouble with RSS 2.0 is they felt there were ambiguities in it – that constraints were too loosely defined and it was too easy to generate a ’sloppy’ XML feed. One of the reasons for Pie/Echo/Atom was to create a tight, well-defined feed that also allowed room for future growth. This type of rigor implies either that you use DTDs or XML Schema to ensure similar behavior. Or you use RDF/XML.

Folks ask me to prove the worth of RDF/XML. I think at this point I’ll turn this one around – I’ll ask the “RDF Tax” folks to prove to me that vanilla XML provides the same precision in both meaning and implemented behavior as RDF/XML – and still be ‘readable’.

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