Meaning, Semantics and RDF

Joe Gregorio

Many things in life are cyclical, and one them is the recurring debates about RDF and the Semantic Web. I don't think the Semantic Web will ever work. Am I trying to discourage people from working on it? No. Keep working away, who knows, I could be wrong and something worthwhile may come of it, but I doubt it. This essay is about hightlighting that doubt.

First, the XML serialization of RDf is cryptic. Tim Bray makes very good points in his two posts about the difficulty of working with the XML serialization of RDF. It is also a point I make in XHTML+XForms+XLink=Xanadu. In that essay I was talking about XHTML versus HTML, but the argument applies just as well to XML versus RDF, that is, RDF in no way moves you up a level of abstraction.

But let's ignore the XML serialization, assume it gets fixed to something perfectly legible and amenable to "view-source". What of it? Well, I have also previously made the point that many of the promises that the RDF proponents make are realizable today with plain XML and we don't need to wait for RDF. This is the crux of the Well-Formed Web, both the essay and the web site, where I am demonstrating with working applications the practicality of the approach. But let's ignore that for now.

Finally, for the sake of argument, I'll also ignore that meanings change over time, people are stupid, people are lazy, people lie, and that there's more than one way to describe something.

Let's focus on the root of RDF, from Tim Berners-Lee, it's raison d'etre.

The Web was designed as an information space, with the goal that it should be useful not only for human-human communication, but also that machines would be able to participate and help. One of the major obstacles to this has been the fact that most information on the Web is designed for human consumption, and even if it was derived from a database with well defined meanings (in at least some terms) for its columns, that the structure of the data is not evident to a robot browsing the web. Leaving aside the artificial intelligence problem of training machines to behave like people, the Semantic Web approach instead develops languages for expressing information in a machine processable form.

This document gives a road map - a sequence for the incremental introduction of technology to take us, step by step, from the Web of today to a Web in which machine reasoning will be ubiquitous and devastatingly powerful.

This is the basics of the Semantic Web and for me it's very telling the TBL raises, then discards, artificial intelligence. It is telling because what he is talking about here is meaning. What does it mean? The whole Semantic Web initiative is based around the idea that you can boil human thought down into a machine digestable format. I can see the allure. For example, search is hard. That is, if I do a search on google for 'adagio', am I looking for the dictionary definition, the company, or the dog? The search engine is really searching for a web page that best matches what I mean when I say adagio. Now here's the crux, for me meaning is what happens when data reaches an intelligence. Consider the word "adagio". What is it. Well right now it's either a pattern of pixels on a screen, or if you printed this out, it's a pattern of ink on paper. Your eye detects the shapes, your brain processes the words and your brain assigns it meaning. Nothing more. If this essay is loaded up by computer it is nothing more that a string of bytes to be processed. Machines can do some pattern matching, indexing, referencing, and various other calculations, but meaning only comes from an intelligent entity.

Yes, I said entity instead of person. First, theres a good chance that there are primates and other animals that may be capable of higher thought and reasoning, and they are capable of assigning meaning to symbols. Unlike Tim Berners-Lee, I'm not so quick to dismiss the AI aspect, because I do believe that someday we will have artificial intelligences, and they will have to navigate not just the formalized halls of an RDF world, but will have to interact with the messy, fuzzy, contradition filled world the rest of us live in. And believe me, there's no RDF out here.

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