A Wordnet from the Ground Up

102 Chapter 4. Extracting Relation InstancesStill, lexico-syntactic patterns are worth attention from the perspective of expandinga wordnet. Their accuracy in identifying instances of wordnet relations is much higherthan the accuracy of the MSRlist (x,k) lists (constructed using an MSR) – see themanual evaluation in Section 3.4.5. Each pattern is also focused on instances of onesemantic relation, mostly hypernymy. In this way, patterns can be a valuable source ofknowledge, complementary to MSRs. This has been the approach in Caraballo (1999,2001) (Section 4.5.3).4.1 Lexico-Morphosyntactic PatternsThere are few known applications of the pattern-based paradigm to Polish. Martinek(1997) and Ceglarek and Rutkowski (2006) presented attempts to apply patterns toMRDs. In an application to a corpus, Dernowicz (2007) performed a simple experiment:using lexico-syntactic patterns to extract meronymic and hypernymic pairs fora very limited set of words in a limited domain. The major obstacles are the lack ofavailable electronic dictionaries and problems with preprocessing text in Polish. Whenprocessing English, a chunker can pick noun phrases and this reduce the complexityof the text is reduced before patterns are applied. Nearly fixed word order also helps.It is not so in Polish: no chunkers or shallow parsers are available (see the discussionin Section 3.4.3). The word order is much freer; as an example, consider two almostsynonymous expressions that both point to the same instance of hyponymy:wieloryb jest ssakiem (whale case=nom is mammal case=inst )ssakiem jest wieloryb (mammal case=inst is whale case=nom )Polish verb arguments are marked by grammatical case, so the morphosyntacticproperties of words encode much of the syntactic structure – Section 3.4.3. We cantherefore reapply to pattern identification the processing methods presented there. Wehave built an IPIC subcorpus (we named it HC) with some 80000 sentences thatplWordNet signals as containing LU pairs linked by hypernymy. Hearst’s patterns(Hearst, 1992) were the first inspiration for discovering patterns for Polish. We alsomanually examined several hundred sentences from HC, looking for characteristic configurationsof LUs. Rather naturally, we were guided by language intuitions. TheEstratto algorithm (see the next section) automatically extracts patterns and instances;its results were another interesting source of ideas. Although Estratto produces rathergeneric patterns, some such simple patterns became a starting point for the manualdevelopment of more refined versions.A pattern imposes lexico-morphosyntactic constraints on the elements of a text fragmentand their mutual dependencies. We implemented the constraints in the JOSKIPI