From Search Engines to Question Answering Systems – The Problems of World Knowledge, Relevance, Deduction and Precisiation1

Existing search engines, with Google at the top, have many truly remarkable capabilities. Furthermore, constant progress is being made in improving their performance. But what is not widely recognized is that there is a basic capability which existing search engines do not have: deduction capability – the capability to synthesize an answer to a query by drawing on bodies of information which reside in various parts of the knowledge base. By definition, a question-answering system, or Q/A system for short, is a system which has deduction capability. Can a search engine be upgraded to a question-answering system through the use of existing tools – tools which are based on bivalent logic and probability theory? A view which is articulated in the following is that the answer is: No. The first obstacle is world knowledge – the knowledge which humans acquire through experience, communication and education. Simple examples are: “Icy roads are slippery,” “Princeton usually means Princeton University,” “Paris is the capital of France,” and “There are no honest politicians.” World knowledge plays a central role in search, assessment of relevance and deduction. The problem with world knowledge is that much of it is perception-based. Perceptions – and especially perceptions of probabilities – are intrinsically imprecise, reflecting the fact that human sensory organs, and ultimately the brain, have a bounded ability to resolve detail and store information. Imprecision of perceptions stands in the way of using conventional techniques – techniques which are based on bivalent logic and probability theory – to deal with perception-based information. A further complication is that much of world knowledge is negative knowledge in the sense that it 1 This paper draws in part on Toward a generalized theory of uncertainty (GTU) – an outline, Inform. Sci. 172 (2005), 1–40. FUZZY LOGIC AND THE SEMANTIC WEB Edited by Elie Sanchez © 2006 Elsevier B.V. All rights reserved