A Wordnet from the Ground Up

5.3. Lessons Learned 177In the end, we took the dictionary of Piotrowski and Saloni (1999) to completethe set of lemmas for the core plWordNet. This was necessary during the semiautomaticexpansion of the nominal part of plWordNet (Section 4.5.4). We also brieflyexperimented with translating into Polish LUs from the upper levels of the nominalhypernymy structure in PWN. This resulted in many artificial LUs – unlexicalisedmeaning descriptions. We were more successful with a simple kind of “machine translation”applied to the verbal and adjectival parts of PWN. For each lemma occurringin the preselected part of PWN, we added to the list all its translations found in theelectronic version of the dictionary of Piotrowski and Saloni (1999). We did not try todisambiguate translations, because we were interested in completing the list of lemmas,which was further processed manually. Moreover, the dictionary is a small pocket dictionary,so it should contain only the most general lemmas, and thus it acts as a kindof filter which eliminates translations for all infrequent LUs.The weakness of the initial lemma list was problematic when expanding the coreplWordNet via the WordNet Weaver (Sections 4.5.3 and 4.5.4): missing hypernyms– LUs from the upper parts of the hypernym structure – affected the accuracy of thealgorithm.The assumption that the LU is the centrepiece of plWordNet (Section 2.1) wasnot uncontroversial: synsets are key elements in most applications of a wordnet. Theresulting structure, however, is not without advantages. The assumption is well motivatedby the linguistic tradition and the lexicographic practice. The rules for addingnew LUs, instances of semantic relations and, especially, LUs to synsets were systematicallydefined following the established linguistic tradition, and implemented in theplWordNetApp application (Section 2.4) as automatically filled substitution tests.Synonymy is an elusive relation, not easily defined, yet it underlies the centralnotion of a synset. The construction of synsets in many wordnets is thus based on impreciserules and on references to the extralinguistic properties of LUs. In plWordNet,a synset is defined through the lexico-semantic relations among its members; moreprecisely, it is the other way round – the similarity of several LUs due to the sharedset of lexico-semantic relation targets 6 makes them candidates for the same synset.In the identification of synsets, hypernymy and meronymy have been distinguished asdefining the structure (Section 2.1). This means that plWordNet (and generally anywordnet designed according to our method of defining synsets) is a network of LUsconnected by lexico-semantic relations. A synset is in this case just a “shortcut” forthe fact that two or more LUs share the same relations. The structure of plWordNetis based on the lexico-semantic relations among LUs, which are well established inlinguistics and for which substitution tests are well known, so the linguists are likelyto make highly consistent decisions.6 For a LU x, all LUs in some lexico-semantic relation with x are such targets.