Ontology: “An explicit formal specification of how to represent the objects, concepts and other entities that are assumed to exist in some area of interest and the relationships that hold among them.” and “The hierarchical structuring of
knowledge about things by subcategorising them according to their essential (or at least relevant and/or cognitive) qualities.”
David Galbraith writes:
Google is a search engine, and does pretty much what Altavista did 5 years ago, before they stopped being just a search engine. They sensibly ignore meta tags, but that was largely to do with people deliberately entering false information. Yahoo’s category search (Yet Another Hierarchical Officious Oracle) is becoming a search engine ‘Yase’ because its difficult to impose ontologies on the web as a whole.
Things that aren’t really search engines, like Amazon and Ebay, or the classification of species for that matter, would be useless without some kind of ontology.
Even without a complete hierarchical system for classification, metadata is useful where pure full text search fails. Try searching for a cheap flight on Google, you can’t – unless they scrape the metadata.