A Wordnet from the Ground Up

4.4. Benefits of Extracted Patterns 129runs of Espresso/Estratto or browsing the corpus to find occurrences of promising LUpairs. A similar problem is with finding the appropriate parameter values. In ourexperience, trial runs of the algorithm for each corpus used are needed before gettingresults that satisfy our expectations.Additionally it turned out that in order to maintain a stable representation of relations,there must be an appropriate ratio between patterns and instances. The pattern:instancesratio estimated during experiments is between 1:15 and 1:20. If thereare fewer instances, the algorithm becomes unstable. Using more instances results ina longer computation time.An interesting result is the observation of the “intensifying” patterns. Such patternsdo not represent any particular semantic relation. When applied alone, they extractinstances of relations of multiple types. When an intensifying pattern is combinedwith regular ones, it delivers additional statistical evidence to correct but infrequentinstances. This lift the algorithm’s precision. An example (Polish w means “in”):(hypo/holo:subst:nom) w (hyper/mero:subst:inst)We observed a problem with the number of instances collected by the ESP+/EST+versions of the algorithms that use generic patterns. This number is comparable tothe number of instances extracted by ESP-/EST-, but one would expect it to be muchhigher. This might be a result of the characteristic features of the IPIC corpus or of thesize of the validating corpus. This problem might be partially solved by using the Webas a validating corpus. Unfortunately, Polish LUs have multiple word forms, so Googlequeries must be more complicated. The other reason might be the limited expressivepower of the patterns – an aspect of the algorithm that should be investigated.The extended structure of Estratto patterns still seems to miss some lexico-semanticdependencies, especially in stylistically rich text. The experiments on extracting hypernymyfrom the Internet-based corpus, mostly consisting of literary texts, were unsuccessful.The first step towards strengthening patterns is to take into account possibleagreements in elements of the patterns that match the instances. The patterns used inEST are very strict about grammatical categories. For example, the pattern(hypo:subst:gen) i inny (hyper:subst:gen)(two nouns in genitive) is treated as a completely different pattern from(hypo:subst:inst) i inny (hyper:subst:inst)(two nouns in instrumental).