Raising and Control Constructions in a B ulgarian UD Parsebank of Parliament Sessions (2022)

Abstract: The paper discusses the raising and control syntactic structures (marked as ‘xcomp’) in a UD parsed corpus of Bulgarian Parliamentary Sessions. The idea is: to investigate the linguistic status of this phenomenon in an automatically parsed corpus, with a focus on verbal constructions of a head and its dependant together with the shared subject; to detect the errors and get insights on how to improve the annotation scheme and the automatic detection of this phenomenon realizations in Bulgarian.

## introduction in the universal dependencies (ud) syntactic guidelines the dependancy relation xcomp is viewed as a clause that belongs to the group of core arguments together with csubj and ccomp. it is used in two cases: a) in constructions with obligatory control @xcite and usually non-finite (for example, in the sentence 'i want to sleep', the non-overt subject of 'sleep' is determined by the overt subject 'i' of the higher predicate 'want'), and b) for the respective types of secondary predication (for example, in the sentence 'she declared the cake beautiful' the predicates 'declared' and 'beautiful' are connected through xcomp). in this survey i am interested in the open clausal complements only, i.e. 'a predicative or clausal complement without its own subject'. as the guidelines further say: 'that is, there should be no available interpretation where the subject of the lower clause may be distinct from the specified role of the upper clause. in cases where the missing subject may or must be distinct from a fixed role in the higher clause, ccomp should be used instead @xcite . this includes cases of arbitrary subjects and anaphoric control.' 1 the aim in this paper is to observe the xcomp types of subject-to-subject control structures in an automatically parsed parliamentary corpus for bulgarian. i am interested in the following questions: a) what kind of control syntactic structures were realized with respect to a main and a controlled predicate; b) what kind of subjects were realized in the control structures -both formally and semantically; c) were any error types detected within the observed structures; d) how do these observations contribute to the linguistic typology of bulgarian control structures and to their better modeling and detection. i consider the linguistic investigations over parsebanks as a way to identifying real language problematic phenomena for parsing beyond the already modeled constructions in grammars, annotation schemes and manually annotated treebanks. i also believe that they give us hints on how to improve the coverage of a treebank (for example, through the means of active learning) for better linguistic research. the paper is structured as follows: in the next section the details on the parsed corpus as well as on the used model are given. section 3 focuses on the relation xcomp with respect to the above mentioned research questions. section 4 concludes the paper. ## the ud parsebank of bulgarian parliamentary sessions this study was performed over the bulgarian par-lamint corpus 2 because it has been annotated with respect to the ud schema and is freely available for research. in future, the plan is to extend the texts in the parsebank with newsmedia and social media corpora, among others. parlamint foot_2 is a project supported by clarin-eric foot_3 . its first phase -parlamint i -was completed in the period of years 2020 -2021. parliamentary data directly correspond to the most recent events with global impact on human health, social life and economics such as the current covid-19 pandemic. the bulgarian parlamint corpus contains plenary meetings from 2014-10-27 to 2020-07-31 and includes 717 documents, or 19,096,761 words. the data is publicly available from the project website. now in the subsequent project phase -par-lamint ii (2022 -2023) -more data have been compiled to the current corpora, and parliamentary corpora for new countries have been added. the bulgarian parliamentary data was downloaded from the official website of the bulgarian national assembly foot_4 . the sessions for each day were represented in a single html file which was relatively easy to convert to xml. the conversion was performed in an incremental way. initially, the data was converted into a basic tei xml format and then uploaded into the clark system - @xcite . afterwards, the parla-clarin format foot_5 was used for validation. however, this turned out to be too permissive, so an additional constraint schemata were applied. within clark system the conversion was done with the help of constraints (as implemented rules) and regular grammars for inserting some elements. the speaker information (such as date and year of birth, occupation, party memberships, personal web page, etc.) and incident data (such as applause, laughing, entering or leaving the plenary room, noise, etc.) were extracted, classified and returned back into the texts with the appropriate features added. thus the present linguistic research can be extended in future with adding more society-oriented features from the available metadata -like which member of parliament uses what control constructions and with what a reference, etc. the created corpora were processed with the classla-stanfordnlp pipeline, which annotates text on the levels of morphosyntax, lemmas, dependency syntax and named entities for bulgar-ian, croatian, serbian, and slovene. 7 this model is a classla fork of the official stanford nlp python library for many human languages. the bulgarian part was trained with the ud bultreebank model and on the provided big corpus of bulgarian data. the resulting analyzed corpus of parliamentary sessions was uploaded into the clark system where it was possible to search for respective subtrees related via xcomp within the ud syntactic structures. the extracted patterns include the control verb, the dependant verb and the subjects when they are explicit at the higher or lower verb level (although in xcomp constructions an explicit subject at the lower clause is not expected). in figure 1 an example in xml of an extracted pattern is given from the clark system. the sentence is as follows: but not can-1.pl to give-1.pl more money, 'however, we cannot give more money either'. the xcomp relation connects the verb in the higher clause -'can' -with the one in the lower clause -'give'. both subjects are not overt. in figure 2 three examples are graphically visualized where the head and dependant verbs are related through xcomp. in the tree on the top-left the following sentence is given (here glossed, and all that follow are also glossed): can-2.pl to check-2.pl (you can check). in this subject-to-subject control both subjects are null since bulgarian is a pro-drop language. we consider this structure as a true control one because the subject of the verb in the lower clause -'check' -is the same as the one of the verb in the higher clause -'can'. in the tree on the top-right the following sentence is given: raynov will come to them.clitic take (raynov will come to take them). here the main verb 'come' has an explicit subject -the surname raynov -in contrast to its dependant verb 'take'. i do not consider such a structure a true control one, since the verb 'come' can take dependant verbs with a different subject. one test that can be used here is the possible substitution of the marker да (to) with the subordinator за да ('for to', in order to). in the example the subjects of the two verbs are the same. we would like to have a way to distinguish such cases in parsebanks. in the tree in the bottom-middle, the following sentence is given: how would could to happen this? (how could this happen?). here the explicit subject is realized to the dependant verb 'happen' in contrast to the main modal verb. however, here many other factors play a role. for example, the adjacency of the pronominal subject either to the main or to the dependant verb with respect to the illocutionary force -interrogative in this case. i view such patterns as formally controlling. all the patterns presented here were used as templates in the process of extracting a subcorpus for the current study. ## the xcomp realisations and their analysis the control verbs are usually discussed on a par with the raising ones. the literature on control and raising verbs from a theoretical or a specific language point of view is very rich and sometimes controversial. for that reason i will mention now only the work on control and semantic resource sensitivity by @xcite . the author gives an overview of the main approaches and proposes a structure sharing alternative for both -non-finite and finite control. the analysis is based on glue semantics and is performed within the framework of lfg. in the original constituency bultreebank (later converted into the ud style), the control structures were not specially marked as such. there was a mechanism to indicate the same subject in the syn-proceedings of clib 2022 tactic structures via co-reference links. however, these links reflected the contextual usages of samesubject-hood, not the real control. thus, they can be viewed as overgenerating. this means that no real distinction was made between structures of control where the predicate imposes on its dependent the same subject in all contexts, and structures where the same subject is not obligatory and thus would allow the appearance of different subjects. making such a differentiation is not a trivial task per se. at the same time, the fact that raising verbs do not impose any restrictions to their subjects (expletive as a rule) has been reflected by assigning the referential subject to the lower clause verb. ## conclusions in this paper some focused observations were shown on the behaviour of bulgarian structures of raising/control in an automatically parsed ud corpus of parliamentary sessions. the manual checks over the extracted data confirmed the high quality of the ud parser on these data. thus, it became possible to detect for example the 'true' control structures vs. quasi control structures. the overgeneration seems to be inherited from the bultreebank model where all cases of shared subjects were marked as coindexed. due to the distinction between active (nsubj) and passive (nsubjpass) subjects in the ud schema, it was possible to survey the internal structure of control and observe the preferences of dependant predicates with respect to their control heads to active or passive usages. one of my goals in this study was also to detect weaknesses in the bulgarian ud treebank which needs some extensions of the annotation patterns in order to provide better parsed corpora for linguistic research. i think that these analyses of control constructions in the current version of the corpus show the following directions of future work: extension of the treebank coverage with new texts that would demonstrate some of the problematic cases for the parser. my observations showed that it is difficult to distinguish between similarly presented phenomena in texts, such as control and quasi control structures. these phenomena might be approached by using lexical lists with both types of verbs. however, this is not enough because their contextual realizations also have to be taken into account. in my view the challenge behind the automatic annotation is to find the best balance between lexicon and grammar. if such a balance was achieved, then the parser would be more linguistically informed and would classify proceedings of clib 2022