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The Meaning of Semantics June 17, 2007

Posted by Andre Vellino in Semantics, Statistical Semantics.
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I worry that the use of “semantics” has become so ubiquitous as to be close to meaningless. For instance, a recent blog post on ReadWriteWeb claims that Hakia offers a practical, “semantics-based” solution to the information retrieval problem on the web.

Sometimes I think this use of “semantics” is intended merely to be synonymous with “better than syntax.” It must be the marketing department trying to commercialize (dumb down?) a complex notion. OntoSem (one of the tools on Hakia-Lab) has a respectable pedigree – even if you disagree with its premise. It is the brain child of Victor Raskin, founder of the Natural Language Processing Laboratory at Purdue and author of Ontological Semantics, who has a web site to promote the book and its ideas.

So Haika Labs and Raskin know what “semantics” means – or at least they operate with one of its accepted definitions in contemporary cognitive science: the machine representation of meaning.

But what is one to make of phrases like:

[OntoSem offers] an ontological parser which “translates” every sentence of the text into its text meaning representation, approximating the complete understanding of the sentence by the native speaker.

Are they claiming that they have got a machine that “understands natural language”? We kept hearing this sort of thing during the 5th Generation boondogle. This was a time when marketing departments claimed that machines could “think” and “reason” just because their datastructures are in the language of first-order predicate logic!

I prefer the Google approach. They buy a company like Applied Semantics which beefed up the Wordnet lexical database with category information about proper names (e.g. “Firefox” is_a_kind_of “web browser”, “web browser” is_a_kind_of “software” etc.) and put it to use to help users disambiguate queries. They use all kinds of ingenious tricks like that – both of a lexical kind and a statistical kind – to give us better search, but they don’t make bold (not to say meaningless) claims about being able to do semantics in a machine.

I like formal definition of “semantics” used by logicians. For them, a “semantics for X” means what mathematicians call a “model theory for X”, i.e. a formal system that provides “models” for formulas in X. This sense of semantics may or may not have anything to do with the machine-representation of meaning for sentences in a natural language, I don’t know, but it has the virtue of being clear. Formal models provide an “interpretation” or “satisfy” formulas under well-defined conditions – for example assignments of truth-values to propositional formulae or sets of constants {a,b,c…} to a variable X in predicate statements like p(X). Similarly inspired formal approaches are also used by computational linguists.

The formal approach to semantics doesn’t directly address the Symbol Grounding Problem discussed in one of Peter’s recent posts, but I think it offers some tools for at least formulating the problem.

Comments»

1. Maarten van Emden - August 31, 2007

Bob Kowalski does not like model-theoretic semantics. In spite of the disagreement, you may be interested in his paper. It’s probably on his website, which has been loading for a few minutes now, so it may be down. I’m digging up from memory what hints I can… published in a volume edited by Dov Gabbay mid-nineties maybe with papers about model theory.

2. PowerSet « Synthèse - December 5, 2007

[…] Haika – whose marketing assertions I expressed some doubt about in a previous post – and PowerSet are mentioned in the recent roundup of “Semantic Apps to Watch” on […]

3. Meaning of Semantics Revisited « Synthèse - May 7, 2008

[…] defines semantics as “the study of meaning in communication”. As I have indicated in a previous post I like the formal definition of “semantics for X” wherein expressions in a language […]


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