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“Powerset Hype to Boiling Point”, said a February headline on TechCrunch. In the last installment of this column, I asked whether 2007 would be the year of question-answering. My query was occasioned by a number of new attempts at natural language question-answering that were being promoted in the marketplace as the next advance upon search, and particularly by the buzz around the stealth-mode natural language search company Powerset. That buzz continued with a major news item in the first quarter of this year: in February, Xerox PARC and PowerSet struck a much-anticipated deal whereby PowerSet won exclusive rights to use PARC's natural language technology, as announced in a VentureBeat posting. Following the scoop, other news sources drew the battle lines with titles like “Can natural language search bring down Google?”, “Xerox vs. Google?”, and “Powerset and Xerox PARC team up to beat Google”. An April posting on Barron's Online noted that an analyst at Global Equities Research had cited Powerset in his downgrading of Google from Buy to Neutral. And, all this on the basis of a product which, at the time of writing, very few people have actually seen. Indications are that the search engine is expected to go live by the end of the year, so we have a few more months to wait to see whether this really is a Google-killer. Meanwhile, another question remaining unanswered is what happened to the Powerset engineer who seemed less sure about the technology's capabilities: see the segment at the end of D7TV's PartyCrasher video from the Powerset launch party. For a more confident appraisal of natural language search, check out the podcast of Barney Pell, CEO of Powerset, giving a lecture at the University of California–Berkeley.
Back at the beginning of 2000, I was a member of a working group tasked to come up with some guidelines for revamping my University's website.During one of our meetings, someone made the suggestion thatdecisions about howto structure and present information on the website should be driven by the kinds of questions that users come to the site with.Suddenly a light went on, and there appeared an idea for data gathering that might provide us withsome useful information. To find out what people really wanted to know whenthey visited the website, we would replace the University's searchengine by a page that invited the user to type in his or her query as a full natural language question. Appropriately chosen examples would be given todemonstrate that using real questions delivered better pages as a result. The data gathered would tell us what people were really looking for, more than could be gleaned from conventional search queries, and would therefore help usto better structure the information available on the website.
Parsing unrestricted text is useful for many language technology applications but requires parsing methods that are both robust and efficient. MaltParser is a language-independent system for data-driven dependency parsing that can be used to induce a parser for a new language from a treebank sample in a simple yet flexible manner. Experimental evaluation confirms that MaltParser can achieve robust, efficient and accurate parsing for a wide range of languages without language-specific enhancements and with rather limited amounts of training data.
The subject of this book is constraint logic programming, and we will present it using the open source programming system ECLiPSe, available at http://www.eclipse-clp.org. This approach to programming combines two programming paradigms: logic programming and constraint programming. So to explain it we first discuss the origins of these two programming paradigms.
Logic programming
Logic programming has roots in the influential approach to automated theorem proving based on the resolution method due to Alan Robinson. In his fundamental paper, Robinson [1965], he introduced the resolution principle, the notion of unification and a unification algorithm. Using his resolution method one can prove theorems formulated as formulas of first-order logic, so to get a ‘Yes’ or ‘No’ answer to a question. What is missing is the possibility to compute answers to a question.
The appropriate step to overcome this limitation was suggested by Robert Kowalski. In Kowalski [1974] he proposed a modified version of the resolution that deals with a a subset of first-order logic but allows one to generate a substitution that satisfies the original formula. This substitution can then be interpreted as a result of a computation. This approach became known as logic programming. A number of other proposals aiming to achieve the same goal, viz. to compute with the first-order logic, were proposed around the same time, but logic programming turned out to be the simplest one and most versatile.
In parallel, Alain Colmerauer with his colleagues worked on a programming language for natural language processing based on automated theorem proving.