Implementation of the Verb Model in pl W ord N et 4.0 (2018)

Abstract: The paper presents an expansion of the verb model for plWordNet – the wordnet of Polish. A modified system of constitutive features (register, aspect and verb classes), synset and lexical relations is presented. A special attention is given to the proposed new relations and changes in the verb classification. We discuss also the results of its verification by application to the description of a relatively large sample of Polish verbs. The model introduces a new class of relations, namely non-constitutive synset relations that are shared among lexical units, but describe, not define synsets. The proposed model is compared to the entailment relations in other wordnets, and the description of verbs based on valency frames.

## semantic classes the plwn 2.0 top part of the verb hypernymy structure consisted of artificial synsets expressing verb semantic classification originating from 7 classes of @xcite : processes, actions, acts, accidents, activities, events, states, were defined on the basis of @xcite . this classification resulted in a large number of subclasses that constrained the rest of the verb hypernymy structure. this classification system was sophisticated and potentially useful in applications, but appeared to be very hard to be applied consistently by wordnet editors @xcite , especially as the verb classes constrain verb relations in plwn. after analysis of the editing practice and the obtained results, the classification was simplified with only two main classes left in plwn 4.0: state and dynamic verbs. this basic division corresponds to the general linguistic tradition, cf e.g. @xcite @xcite , polish, e.g. @xcite , and also ewn. vossen (2002) defines dynamic verbs as: the subclass definitions (summarised above) are formulated in an operational way, on the basis of several substitution tests. they are referred to in relation definition and support linguists in editing. thus, semantic class is a constitutive feature, together with stylistic register and aspect. semantic subclasses of dynamic verbs are clearly connected to several relations that are characteristic for this class, namely: processuality, causality, inchoativity and multiplicativity. only state verbs can participate in state relation. other types of relations occur in both verb classes. verb classification is expressed by a hierarchy of artificial lus (represented by singleton synsets) as in @xcite . class assignment is done by placing a verb in an appropriate hypernymic branch, as hyper/hyponymy and synonymy (due to relation sharing) requires equality of semantic classes. semantic subclasses clearly refer to wellknown linguistic classifications of verbs, e.g. @xcite and support wordnet editors in building hypernymic trees on the basis of semantic properties of verbs. the reduction of the number of classes (from 7 to 2) should facilitate identification of only real verb meanings and prevent introduction of non-natural and too fine-grained meanings. ## entailment verb entailement relation plays an important role in pwn and germanet, which is defined by @xcite as: in addition, @xcite introduces four subtypes of entailment. in plwn a more finegrained division of the spectrum of verb relations is proposed, see the comparison in we can notice a different perspective on situations co-occurring in the same time period. in pwn it is always represented by troponymy, which is defined as a kind of entailment (see sec. derivational prefixes of verbs are important semantic signal in polish. so far, verb prefixes have been only selectively and implicitly described as correlated with relations signalled by derivations. although, we have not yet studied this issue in a ewn entailment +temporal inclusion -temporal inclusion co-extensiveness -troponymy proper inclusion backward presupposition cause plwn hyponymy, meronymy meronymy presupposition, preceding cause systematic way, some associations between prefixes, meanings and lexico-semantic relations became visible. prefixes do-, wy-can signal situations in which an agent is accomplishing his goal, e.g. dojść 'to have reached sth', dokopać się 'to have dug down to sth', wysiedzieć 'to have continued sitting until sth happened', wyczekać 'to have continued waiting ...'. they express a relation to a goal or an end that are often implicit. another example is a set of prefixes expressing a kind of manner relation in the case of delimitative verbs: po-and do-. concerning the first, poprefix means to do a little, e.g. posiedzieć 'to sit a little' (siedzieć `to sit'), pooglądać 'to watch a little' (oglądać to watch). the prefix do-signals more advanced or intensive situation, e.g. doszkolić się 'to improve qualifications' (szkolić się `to learn by himself'), dogęszczać 'to thicken more (a mixture, substance etc.)' (zagęszczać `to make thicker'). verbs derived by prefixes are linked by secondary aspectuality, e.g. wysiedzieć 'to have continued sitting' -siedzieć 'to sit' or by more specific relations, e.g. inchoativity. however, secondary aspectuality is intentionality vague, only slightly more informative than fuzzynymy, and is a way of registering lu pairs requiring deeper investigation in future. a more in depth exploration of derivational verb prefixes focused on enrichment of wordnet relations is a very interesting task to be undertaken in the future. so far, the number of verb lemmas in plwn has been increased to 19,272 i.e. by 11%. in parallel, we have updated the verb hypernymy structures and verb relations to a large extent. this enabled us to observe the changes triggered by the new verb model. tab. 2 present statistics for the relations and changes in relations. we can notice that the modification of the model resulted in the increased frequency of the following relations: processuality, causality, presupposition, inchoativity, state. in the same time the number of verb meronymy instances has decreased but this could be expected due to the more stricter definition and the remove of the ambiguous division into two subtypes (this ambiguity led to too far going interpretations). ## verb model vs valency lexicon a high quality valency dictionary with good coverage is an indispensable resource for many nlp applications. unfortunately, its construction is very laborious and costly. plwn model defines a rich system of verb relations. the question is to what extent it can supplement a valency lexicon? @xcite argues that semantic roles are indispensable in the description of the predicate-argument structures, e.g. the agens role refers to the logical subject of a predicate, while the theme and patiens roles to the logical objects. a clear reference made in the plwn verb model to the syntactic-semantic relations is aimed at improving richness of lu descriptions following @xcite who argues that a dictionary should provide description of co-occurrences of lexico-semantic and syntactic features. in czech wordnet @xcite valency frames are added to synsets. however, we assumed in plwn that syntactic valency is not a constitutive feature of verb lus, and does not need to be shared by synset members, so is not used to define synsets. it could be described on the level of lus, but this is in fact done in walenty @xcite , a large valency lexicon of polish. thus, syntactic valency is not expressed in plwn, a semantic lexicon, and there are no plans for introducing it. so, this part is clearly missing, but verb arguments which are mentioned in relation definitions can be implicitly expressed in the lexico-semantic relations. as a consequence, quite a lot of information about semantic restrictions on valency arguments is hidden in plwn relations. it is partial and selective, but still can be useful. three relations introduced in plwn 4.0 directly evoke structure relations, namely: subject (referring to the semantic agent role), object (patient role) and circumstance, whose detection is based on prepositional phrases, which can correspond to other roles, for example location, result, time. as it was said in sec. 2, subject, object and circumstance relations (manner does not link nouns) are not constitutive relations, but emphasise selected aspects of lu meanings that are common to the whole synset, and in the same time relate these aspects to the syntactic structure, e.g. circumstance links brzeg `a shore' with dobijać `to reach a shore' informs also that one of the dobijać predicate arguments represents location. in a similar way object relation links usypiać 'to put down, to put to sleep, to euthanize' with zwierzę 'an animal' and signals that one of the arguments repre-sents animal or its hyponym. the guidelines instruct to find for these relations nouns that are located on relatively high levels of the hypernymy to describe the meaning of the verb lu, not its collocational behaviour. linguists are also required to check if most of the hyponyms of the selected target noun fulfil the tests for this relation. in the same time the target noun should not be located too high in order to preserve meaningfulness of the link, i.e. lus from the top level of the hypernymy hierarchy should be avoided, e.g. byt 'an entity', istota 'a being'). in walenty semantic description is based on selectional preferences: "lexico-semantic dependencies between a unit which is a predicate of an utterance and units that are its arguments, that determine what kind of notions can co-occur on the subsequent valency arguments" @xcite . because walenty frames have been built in relation to the plwn lus, selectional preferences of the walenty entries tend to be correlated with plwn synsets. @xcite aims at encompassing by selectional preferences all hyponyms of a given synset, e.g. for rżeć 'to neigh' there are two semantic frames: selectional preferences of the first restrict agent ("initiator") to koń 'a horse' (plwn: koń 1 `a horse') and in the second to człowiek `a man' characterising the second meaning of rżeć as `to laugh producing sound resembling neighing'. selectional preferences in walenty are chosen according to the frequency, i.e. in the case of rżeć 'to neigh' the editor decided that the constraint koń `a horse' for the agens is enough frequent to be expressed in the frame; in addition, all hyponyms of koń `a horse', e.g. pegaz 'pegasus-like', gniadosz 'a bay', but also derivates, i.e. diminutives e.g. konik '~a litle horse' and augmentatives, e.g. konisko '~a large, not pretty horse' are included in the preferences. plwn describes the subject link between rżeć 'to neigh' and koniowate 1 'an equine', because also zebras or giraffes are neighing (at least in polish) and they belong to equines taxonomy together with koń `a horse'. these links can be further interpreted by explicit derivational links. semantic valency information can be also found in lexical relations: role (n-v, describing deverbal nouns) role inclusion (v-n, verbs derived from nouns). both relations have 7 subtypes: agens, instrument, product, location, patiens, time and indefinite subtype @xcite that refer to thematic roles of @xcite , on the one side and to the studies on the semantics of deverbal nouns in the polish literature, cf @xcite . both relations tell something about the selectional preferences. for instance solić 1 'to salt' is a hyponym of przyprawiać 2 'to spice' and means `to spice with salt' and is linked with sól 'salt' by role_inclusion:instrument as a verb derived from a noun -a tool name. the expression solić solą `to salt with salt' is redundant and incorrect, but one can say przyprawiać solą 'to spice with salt', where przyprawiać 2 is linked by role_inclusion:instrument to przyprawa 1 ('a spice'); przyprawiać `to spice' can be done by salt or different spices -cohyponyms and cousins of sól 1 `salt'. another example can be bokser 'a boxer' linked by role:agens to boksować 1 'to box' (its derivational basis), which is a hyponym of bić 4 'to hit, to beat'. the expression bokser boksuje is redundant but bokser bije `a boxer is beating' is correct. thus, the combination of role/role inclusion and verb and noun hypernymy can be used to draw conclusions about selectional preferences of the verb arguments. relations defined on the level of synsets go beyond the derivational associations. during the work on plwn 4.0 we have realised that a lot of valuable semantic knowledge is not covered by strictly derivationally motivated relations. analysis of fuzzynymy from plwn 3.0 showed that semantic associations visible in derivations can be cautiously generalised, i.e. in a way based on strict procedure, substitution tests and guaranteeing good consistency among editors. ## conclusion we presented an expanded verb model for plwn, including modified constitutive features, and synset and lexical relations. non-constitutive synset relations were introduced. they are shared among lus in a synset, characterise important aspects of verb meaning, but are not necessary constraints for defining synsets. they seem to be a good tool for the inclusion of knowledge valuable for wordnet applications, e.g., wsd. the proposed model was verified and slightly amended on the basis of its application to a large sample of polish verbs. the first statistical data showing the results of the proposed changes were discussed. we showed that the proposed system of relations provides information about entailment and selectional preferences. open issues are: the relation between the defined lexico-semantic relations and relations between verb valency frames, and the extent of automatization in identification of the selectional preferences on the basis of the relations.