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Proceedings of the Fifth Italian Conference on Computational Linguistics CLiC-it 2018

 | 
Elena Cabrio
, 
Alessandro Mazzei
, 
Fabio Tamburini

Contributed Papers

LatInfLexi: an Inflected Lexicon of Latin Verbs

Matteo Pellegrini et Marco Passarotti

Résumé

We present a paradigm-based inflected lexicon of Latin verbs built to provide empirical evidence supporting an entropy-based estimation of the degree of uncertainty in inflectional paradigms. The lexicon contains information on the inflected forms that occupy the 254 morphologically possible paradigm cells of 3,348 verbal lexemes extracted from a frequency lexicon of Latin. The resource also includes annotation of vowel length and the frequency of each form in different epochs.

Presentiamo un lessico di forme flesse basato sui paradigmi per i verbi latini, costruito per fornire evidenza empirica che permetta di quantificare il grado di incertezza nei paradigmi flessivi tramite l’entropia. Il lessico contiene informazioni sulle forme flesse che occupano le 254 celle possibili dal punto di vista morfologico di 3.348 lessemi verbali estratti da un dizionario frequenziale del latino. La risorsa include anche l’annotazione della lunghezza vocalica e la frequenza di ogni forma in diverse epoche.

Texte intégral

1 Introduction

  • 1 The term “lexeme” is used for the abstract theoretical concept normally adopted in morphology and l (...)

1In this paper, we describe the construction of LatInfLexi, an inflected lexicon of Latin verbs organized in lexemes1 and paradigm cells.

2In morphological theory, there is a recent trend towards a more realistic modelling of complex inflectional systems: for instance, Ackerman et al. (2009) and Bonami and Boyé (2014) propose that the analysis should take a full inflected form as a starting point, without assuming any segmentation a priori. In such approaches, what is investigated is not the construction of forms from smaller units like stems and inflectional endings, but rather their predictability given knowledge of other forms. This can be done by using the information theoretic notion of conditional entropy to estimate the uncertainty in guessing the content of the paradigm cell of a lexeme knowing another inflected form of the same lexeme, by weighting the probability of application of each inflectional pattern based on their type frequency in real data.

3To do so, large-scale inflected lexicons listing all forms of a representative selection of lexemes are needed. Such resources are increasingly being developed for modern languages – see among else Zanchetta and Baroni (2005) and Calderone et al. (2017) for Italian, Neme (2013) for Arabic, Bonami et al. (2014) and Hathout et al. (2014) for French. However, to the best of our knowledge, there are no resources of this kind for Latin, although their (semi-)automatic building is made possible by the current availability of several morphological analyzers for Latin, including Words (http://archives.nd.edu/​words.html), Lemlat (www.lemlat3.eu), Morpheus (https://github.com/​tmallon/​morpheus), the PROIEL Latin morphology system (https://github.com/​mlj/​proiel-webapp/​tree/​master/​lib/​morphology) and LatMor (http://cistern.cis.lmu.de). Our resource was created to fill this gap and to enable a quantitative, entropy-based analysis of Latin verb inflection.

2 Design

4A distinctive feature of our inflected lexicon is that it is based on lexemes and paradigm cells, rather than on forms. This means that for each lexeme, all the morphologically possible paradigm cells are filled with a form, and not only those forms that are indeed attested in Latin texts are stored in paradigm cells. In this respect, our resource is similar to other recently developed inflected lexicons, like for instance Flexique for French (Bonami et al., 2014).

5For each paradigm cell, the following information is provided:

  1. the inflected form that occupies the paradigm cell;

  2. a univocal identifier of the lexeme to which it belongs;

  3. the set of its morphological features;

6information on the frequency of the form in different epochs.

7As for (i), it should be noted that there is never more than one form per paradigm cell. In cases of overabundance (i.e. cells that are filled by more than one form, cf. Thornton, 2012), a choice was made to decide which “cell-mate” (Thornton, 2012: 183) should be kept, and which one discarded.

  • 2 Throughout the paper, we will refer to grammatical features by using the standard abbreviations of (...)

8On the other hand, in some cases a paradigm cell could be empty, either because it is defective – like for instance the passive cells of intransitive verbs – or because it is not filled by a synthetic form, but rather it is analytically expressed, by means of a phrase – like for instance, in Latin, the perfective cells of deponent verbs, for which the periphrasis prf.ptcp 2 + aux esse ‘to be’ is used (e.g. prf.ind.1sg hortātus sum ‘I incited’). In both cases, the cell is marked as #DEF# in the resource. This convention is adopted also in Flexique (Bonami et al., 2014: 2585), and it fits the requirements of the Qumin package for entropy calculations on the predictability of implicative relations between inflected forms (Bonami and Beniamine, 2016; Beniamine, 2017).

9As for (ii), the identifier corresponds to the citation form of the lexeme, almost always the first-person singular of the present indicative, following the Latin lexicographical and didactical tradition. A diacritic is added in those rare cases where different verbs have the same citation form (see infra, §3.2).

10Regarding (iii), we use the PoS-tags of the Universal Part-of-Speech Tagset by Petrov et al. (2012) and the morphological features used in Universal Dependencies (http://universaldependencies.org/​u/​feat/​index.html).

11Lastly, the frequency data in (iv) are taken from Tombeur’s (1998) Thesaurus Formarum Totius Latinitatis (see infra, §3.3).

3 Building the Lexicon

12This section details the procedure followed to build the lexicon.

3.1 Selecting the Lexemes

13Our first objective is to build an inflected lexicon of Latin featuring all the possible inflected forms of verbs only. To this aim, we include all the verbal entries contained in Delatte et al.’s (1981) Dictionnaire fréquentiel et Index inverse de la langue latine (henceforth DFILL). This yields a total of 3,348 verbs. In rare cases, more than one entry of DFILL corresponds to one and the same lexeme in our resource. This happens because some verbs are lemmatized twice in DFILL. For instance, for the verb verso two different entries appear in DFILL, using as citation form both the first-person singular of the present active indicative verso and the corresponding morphologically passive form versor. This choice is likely to be motivated by the different semantics of the two verbs, with the first one meaning ‘to turn’ and the second one meaning ‘to remain’. However, in such cases our resource gives priority to collecting into one common inflectional paradigm all the forms that can be assigned to the same lexeme based on their morphological relatedness, rather than separating them in paradigms of different lexemes according to semantic criteria. Therefore, our lexicon includes only one lexeme verso, for which both active and passive forms are listed.

3.2 Generating the Forms

14In order to fill all of the paradigm cells of the selected lexemes, we exploit the database of Lemlat (Passarotti et al., 2017). For each lexeme, the database of Lemlat contains a list of segments called les – roughly corresponding to the stems that are used in different subparadigms – each with a corresponding codles that provides (among else) information on the inflectional endings that can be attached to a les. We make use of this information to generate the relevant forms.

15To illustrate the details of the procedure, let’s consider the verb rumpo ‘to break’. For this verb, the database of Lemlat features the less and codless shown in Table 1.

Table 1: the verb rumpo in Lemlat 3.0

les

codles

rump

v3r

rumpisse

fe

rup

v7s

rupsit

fe

rupt

n41

rupt

n6p1

ruptur

n6p2

16The two less with codles “fe” (“forma eccezionale”, ‘exceptional form’) were discarded, since they are full irregular forms that are stored as such. As for the other less, the one with codles “v3r” is used to fill all the cells of the present system, by adding the inflectional endings of the conjugation represented by the codles (i.e. the 3rd conjugation). Similarly, the les with codles “v7s” is used to fill the cells of the perfect system. From the remaining less, some nominal forms built upon the so-called “third stem” (Aronoff, 1994) can be derived, namely the supine rupt-um and rupt-ū from the les with codles “n41”, the perfect participle rupt-us, -a, -um from the les with codles “n6p1” and the future participle ruptūr-us, -a, -um from the les with codles “n6p2”.

17This given, our first step is to extract information on the less and codless of each lexeme. Since Lemlat is a tool built to analyze rather than produce forms, it contains also several less occurring only in irregular and/or rare forms. To avoid the risk of overgeneration, we choose and keep only one les for each codles. The choice is based on lexicographical sources, namely Lewis and Short (1879) and Glare (1982). In these dictionaries, at the very beginning of each verbal entry there is a set of four “principal parts” (Bennett, 1908: 55), i.e. exemplary inflected forms from which the whole paradigm of the lexeme can be inferred. We keep only those less that correspond to such principal parts, excluding the ones that correspond to more marginal forms that do appear in dictionaries but are given less prominence in the entry. For instance, Lemlat includes two less with codles “v3r” for the verb dico ‘to say’: “dic” and “deic”. However, in both the lexicographical sources we use, the relevant principal parts are dico and dicere, corresponding to the first les, while the second one is only mentioned later in the entries as an alternative form. Therefore, the les selected for our resource is “dic”.

18We use the same dictionaries also to manually annotate the vowel length for each les. This is a necessary enhancement, because in Latin verb inflection there are homographic forms that can be distinguished only based on that, like for instance prs.act.ind.3sg fugit ‘(s)he flees’ vs. prf.act.ind.3sg fūgit ‘(s)he fleed’.

19Following this process, we fill all the 254 paradigm cells of each of the 3,348 lexemes. However, because of Lemlat’s design, for some quite frequent verbs with a highly irregular inflectional paradigm, it was not possible to apply the same procedure, at least for the cells of the present system, which is where most irregularity of the inflectional endings of Latin verbs happens. For the verbs shown in Table 2 and for those derived from them by prefixation (e.g. abeo ‘to go away’ from verb eo ‘to go’), although it was technically possible to adopt a similar approach by using more than one les for a codles, it proved to be faster and practical to manually record the correct forms as such.

Table 2: irregular verbs

Lemma

Meaning

aio

to say

eo

to go

fero

to bring

fio

to become

inquam

to say

malo

to prefer

nolo

not to want

possum

can

sum

to be

volo

to want

20To each of the 850,392 generated paradigms cells, a univocal lexeme identifier is assigned, which corresponds to the lemma used in Lemlat. In those rare cases where two or more verbs have the same lemma in Lemlat (although they inflect differently), a numeric diacritic is added to make the relevant distinction: for instance, we have volo1 ‘to fly’ and volo2 ‘to want’.

3.3 Frequency Data

21Many forms included in the paradigm cells of our lexicon are never attested in Latin texts. In order to make it possible to distinguish between plausible but unattested forms and those indeed occurring in texts, we enhance forms with information on their frequency. This information is taken from Tombeur’s (1998) Thesaurus Formarum Totius Latinitatis (henceforth TFTL), where each form is assigned the number of its occurrences in four different epochs, respectively called Antiquitas (from the origins to the end of the 2nd century A.D.), Aetas Patrum (2nd century-735 A.D.), Medium Aeuum (736-1499) and Recentior Latinitas (1500-1965).

  • 3 The 97,855 paradigm cells marked as #DEF# are excluded from this count.
  • 4 In total, the TFTL includes 554,828 different forms, corresponding to 62,922,781 occurrences in the (...)

22By including the frequency of each form in the lexicon, we know how many of the 752,5373 forms recorded in the lexicon are never actually attested. Table 3 reports the relevant data4.

Table 3: not attested forms

TFTL epoch

unattested forms (%)

Antiquitas

544,395 (72.34%)

Aetas Patrum

482,324 (64.1%)

Medium Aeuum

484,421 (64.37%)

Recentior Latinitas

640,552 (85.12%)

all epochs

401,690 (53.38%)

23It can be observed that a significant amount of forms recorded in our lexicon are not attested, even in such a large corpus as the one the TFTL is based on. However, this is not surprising: recent large-scale corpus-based investigations (e.g. Bonami and Beniamine, 2016: 158 ff.) show that in languages with large inflectional paradigms – like the ones of Latin verbs – it is perfectly normal that many plausible forms do not appear, even in very large datasets, and the lexemes for which the full paradigm is attested are very few.

4 Discussion and Future Work

24We described the design and building of a lexeme-based inflected lexicon consisting of 850,392 paradigm cells of 3,348 Latin verbs. Our first objective in the near future is to make the resource complete in terms of lexical coverage, including the lexemes of the other PoS. The lexicon is available for download as a .csv file at https://github.com/​matteo-pellegrini/​LatInfLexi.

25We also plan to include phonetic annotation, by giving the IPA transcription of each form, which can be obtained semi-automatically by applying a script provided by the Classical Language Toolkit (Johnson et al., 2014-17) to stems and endings.

26Another welcome addition would be to account for cases of overabundance, by allowing more than one form to appear in the same paradigm cell. However, to decide which cell-mates to keep and which ones to discard, their frequency in Latin texts should be preliminarily evaluated. In this respect, it has to be noted that the frequencies in the TFTL refer to bare surface forms, with no contextual disambiguation. For instance, the frequency of veniam comprises not only occurrences of both the prs.act.sbjv.1sg and fut.act.ind.1sg of the verb venio ‘to come’, but also of the acc.sg of the noun venia ‘indulgence’.

27To get an idea of the impact of morphological ambiguity on our lexicon, we analyzed all the generated forms with Lemlat (version 3.0). We found that only for about 23% (170,735) of the 752,537 forms Lemlat outputs only one analysis (i.e. one lemma and one set of morphological features), the remaining 581,802 (about 77%) being ambiguous. This result weakens the reliability of the frequency data provided in the lexicon. Therefore, disambiguation is needed, although this would require a very time-consuming work.

28However, to tackle the problem of ambiguity, a first useful step is distinguishing between cases like veniam above, which can be analyzed as an inflected form of two different lemmas, and cases where the different analyses only refer to different forms of the same lemma, e.g. laudatis, that appears both in the prs.act.ind.2pl and in the prf.ptcp.dat/abl.pl of laudo ‘to praise’, but cannot be a form of other lemmas. We call these different types ‘exolemmatic’ and ‘endolemmatic’ ambiguity, respectively (cf. Passarotti and Ruffolo, 2004). Cases of exolemmatic ambiguity are clearly more problematic, but they are also much rarer: only 79,490 (about 10%) of the forms in our resource belong to this type. The great majority of ambiguous forms only give rise to endolemmatic ambiguity, as can be observed in Table 4 below, where the relevant data are summarized.

Table 4: the impact of ambiguity on frequency data

n.

%

unambiguous forms

170,735

22.69%

ambiguous forms

581,802

77.31%

only endolemmatic amb.

502,312

66.75%

exolemmatic amb.

79,490

10.56%

29As far as endolemmatic ambiguity is concerned, although its quantitative impact is far greater, it could be considerably reduced in a principled manner. Indeed, it should be noted that in many cases this kind of ambiguity is due to systematic syncretism. For instance, the cells fut.act.imp.2sg and fut.act.imp.3sg are never unambiguously analyzed, because they are always identical for a same verb. Given the full systematicity of this syncretism, which holds for all lexemes, these cells could be considered as only one from a purely morphological point of view. Therefore, the problem of endolemmatic ambiguity could be at least reduced by adopting an approach based on “morphomic paradigms” (Boyé and Schalchli, 2016), where always syncretic cells are conflated, rather than on morphosyntactic paradigms. This would be helpful especially in nominal forms like participles and gerundives, where such cases of systematic syncretism are widespread.

30When such ambiguity issues will have been resolved, it will also be possible to exploit the frequency data in a more systematic fashion, e.g. to perform diachronic investigations on how the frequency of specific (groups of) forms or paradigm cells change across the four considered epochs, or to model Latin inflectional morphology in an even more realistic way, by considering also the token frequency of inflected forms, as has been recently proposed by Boyé (2016).

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Notes

1 The term “lexeme” is used for the abstract theoretical concept normally adopted in morphology and lexicology, while “lemma” refers to the concrete citation form representing an entry in dictionaries. Since we aim at a resource suitable for theoretical inquiries, we use the first term as a label in our resource.

2 Throughout the paper, we will refer to grammatical features by using the standard abbreviations of the Leipzig Glossing Rules.

3 The 97,855 paradigm cells marked as #DEF# are excluded from this count.

4 In total, the TFTL includes 554,828 different forms, corresponding to 62,922,781 occurrences in the reference corpus used by the Thesaurus. Our lexicon contains 165,898 of these unique forms (forms appearing in more than one paradigm cell are counted only once), for a total of 18,261,179 occurrences. This means that our resource covers around 30% of the forms of the TFTL, in terms of both type and token frequency. In addition, it also contains several other forms that are not attested in the TFTL (245,623 unique forms).

Auteurs

Università di Bergamo/Pavia, Piazza Rosate, 2 – 24129 Bergamo, Italy – matteo.pellegrini[at]unibg.it

CIRCSE Research Centre – Università Cattolica del Sacro Cuore, Largo Gemelli, 1 – 20123 Milan, Italy – marco.passarotti[at]unicatt.it

© Accademia University Press, 2018

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