A Wordnet from the Ground Up

1.1. Motivation 11[a] special form of the traditional semantic networks [. . . ] the conceptof a lexical semantic network, the nodes of which represented sets of actualwords of English sharing (in certain contexts) a common meaning 3 .PWN is also referred to as a lexical ontology. As Miller and Fellbaum (2007,p. 210) emphasise, however, PWN was never thought to be an ontology. PWN doesinclude ontological relations – e.g., parts of the hypernymy hierarchy can be analysedas a taxonomy – but prior to the release of PWN 3.0 there was no distinction betweentypes and instances. Even now most relations are linguistically motivated.Our brief overview of the “takes” on the nature of PWN shows how important languageintuitions are, especially for context-dependent synonymy. It all revolves aroundsemantically motivated groupings of LUs. Surprisingly, the central building blocksof a wordnet’s structure are typically not LUs but lexicalised concepts, about whichfew general assumptions are made. This gives a wordnet designer much freedom butprecludes successful comparison, evaluation and especially interpretation of wordnets.The fast-growing number of “national” wordnets (more on that in Section 1.1.4) makessuch inconsistencies problematic. It does not help that, with a few exceptions, thosewordnets are new and rather small 4 .1.1.3 The importance of wordnets for language processingFor those who work with a natural language that lacks a wordnet, the question isnot whether but how and how fast to construct such a lexical resource. The sheernumber of applications and research experiments that rely on PWN (Fellbaum, 1998c)– just consider 868 projects listed in (Rosenzweig et al., 2007, state in Oct. 2008) –shows convincingly how useful wordnets are in NLP. Morato et al. (2004) presenteda broad overview of the different PWN applications at the Second Global WordNetConference; see the discussion of wordnet-related events at the end of this section.Rather predictably, the picture is not so clear when it comes to commercial applications,but PWN’s free availability must have resulted in its inclusion in marketable productsin the general area of language technology. Wordnets for other languages, even quiteincomplete, are useful insofar as they are the only machine-tractable lexico-semanticresources for those languages.The primary use of a wordnet may be as a sense inventory. For example, Agirreand Edmonds (2006, p. 7) characterise PWN as “the most-used general sense inventoryin Word Sense Disambiguation research”. Synsets, used as sense labels attached towords or expressions in text, help perform Word Sense Disambiguation [WSD] (Banerjeeand Pedersen, 2002). Wordnet glosses are often used as a source of training data.3 In general, nodes in semantic networks may be labelled with abstract names.4 See http://wordnet.princeton.edu/man/wnstats.7WN for the current PWN statistics.