A Wordnet from the Ground Up

4.4. Benefits of Extracted Patterns for Wordnet Expansion 119verified. The resulting patterns are run on a validating large corpus (for Espresso, theWeb). A confidence measure is computed from the collected frequencies and comparedwith a threshold.In Espresso, the Internet served as a validating corpus for instances extracted bygeneric patterns. We need other resources because of the paucity of Polish Web pagesand the inherent difficulty of querying regardless of the inflectional variety. A secondlarge corpus (Rzeczpospolita, 2008) (but still much smaller than the data from the Weband even IPIC used for the extraction of the patterns) served the purpose of validationin Estratto. The necessary condition for finding occurrences of the patterns extractedfrom the primary corpus seems to be that the validating corpus cover similar genresand domains.The induction of patterns and the extraction of instances in Estratto are controlledby the following set of parameters:1. the number of top k patterns not to be discarded (preserved for the next iterations),2. the threshold measure of confidence for instances,3. the minimum frequency and maximum frequency values for patterns,4. the minimum size of a pattern – all patterns that consist of only matching locationsand conjunctions are discarded by definition,5. a filter on common words in instances and on instances with identical LUs onboth positions,6. the size of the validating corpus.4.4 Benefits of Extracted Patterns for Wordnet ExpansionWe investigated the use of algorithms like Espresso in order to find method for extractingvaluable instances of wordnet relations, at least hypernymy, with precision higherthan afforded by the handwritten lexico-morphosyntactic patterns. We did not expectready-to-add hypernymy instances. We only wanted to construct yet another sourceof knowledge that suggests hypernymy occurrences and the correct direction of therelation.It is far from trivial properly to evaluate the extracted lexico-semantic resources(Section 3.3). It is much easier for lists of instances: we verify how many of them arecorrect. Only two comparisons were possible for Polish:• with the existing structure of the core plWordNet,• with an evaluation by one of the co-authors.