There exist several morphological dictionaries for Czech. They differ only in solutions of complicated morphological features. Various attempts have been made to unify their approaches, but only some of them were implemented. The paper deals with several such features and compares their solutions taken in two different projects, namely preparation of the new edition of PDT (Prague Dependency Treebank [1]) and NovaMorf [8]. The features presented in this paper are: aggregates (the wordforms without a clear part of speech, e.g. užs, ocˇ, nanˇ), and variants - inflectional (more wordforms for a particular combination of lemma and morphological tag) as well as global ones (mainly orthographic variants expressed in all wordforms of a paradigm).
There are several “classical” parts of speech covering almost the whole vocabulary of any language. Apart from them, there are words, that are difficult to be assigned an appropriate part of speech (POS). During the times, they were carried from one POS to another. Also, the number of POS was changing.
Some words are difficult to place into a right position among POS, because they might belong to more of them. It results in an artificial homonymy – the same word is included into more POS classes and due to formal requirements they should be considered different words. There were many attempts to solve that situation, but no generally accepted solution has been found.
Two recent projects dealing with the Czech
morphology tried to solve at least some issues connected to POS
classes. They are the new edition of PDT (Prague
Dependency Treebank [
According to [
We present several examples together with their explanations1: 1. videˇls = videˇl jsi (you saw) 2. studentas = studenta jsi (e.g. Toho studentas nevideˇl? .. You have not seen that student?) 3. užs = už jsi (you already were) 4. donˇ = do neˇj (into it) 5. nacˇ = na co (on what) 6. nacˇs = na co jsi (on what you were)
Apart from the first example, where the both components are verbs, there are at least two different parts of speech contained in all the aggregates. That fact makes it difficult to assign aggregates one of traditional POS. This is the reason why a new part of speech was introduced to the system of the Czech morphology – Aggregate.
The aggregates can be divided into three groups (aggregate types): 1. Verbal aggregates – those aggregates where the second component stands for the wordform jsi (you are). The first component can be almost any POS (see the examples 1 to 3 above). In NovaMorf, conditional conjunctions aby, kdyby together with all their forms abych, kdybyste, ... are considered also verbal aggregates, which is not the case of the PDT project. 2. Pronominal aggregates – those aggregates where the second component is the pronoun co (what) or neˇj (lemma on = he). The first component is a preposition (see the examples 4 and 5 above). 3. Combined aggregates – those aggregates where the first component is a preposition, the second one is a pronoun co or neˇj (as in pronominal aggregates), and the third component is the auxiliar verb jsi (as in verbal aggregates). It is a combination of the previous two types – verbal and pronominal (see the example 6 above).
1The English translations might seem meaningless without a conThe previous list contains all sorts of Czech aggregates. Having divided the types of aggregates, let us have a look how to morphologically annotate them.
Every wordform should be morphologically described as a unique couple consisting of a lemma and a morphological tag. However, there are different approaches how to do it in case of aggregates. In the following subsections we will introduce two of them, belonging to the two beforementioned projects. 2.1
In the NovaMorf project, the lemma of an aggregate is the sequence of lemmas of all its segments. We call such a sequence a multiple lemma of aggregates.2
According to the previous introductory text, there are at most three different lemmas in the multiple lemma of a Czech aggregate. This may not be the case for other, especially agglutinative languages.
There are only limited number (closed set) of
pronominal and combined aggregates in Czech, that is why it is
possible to describe those types of aggregates by means
of a single morphological tag. The same is possible to
achieve for the verbal aggregates, though there are
extremely productive. The description of such an annotation
is included in [
However, there was quite a big opposition against that solution, so the researchers adopted an alternative (equivalent) solution that is possibly more intuitive. They introduced a concept of multiple tag, as a paralel concept to the multiple lemma. The multiple tag is the sequence of the tags describing all segments of an aggregate. The sequence of tags is ordered in the same way as the sequence of lemmas in the multiple lemma of the aggregate.
The morphological description of the examples presented above are given in the table 1.3 2.2
The project PDT adopted a different solution (see also [
s for verbal aggregates; 2There is another use of the concept of multiple lemma for description of variants. It will be introduced later in this paper. The main difference between the two is that the multiple lemma of aggregates is a sequence, while the multiple lemma of variants can be a set.
3All the tables in this paper are presented with the morphological
tags used in the Prague dictionary Morfflex [
These values are incorporated to the morphlological tag. The particular placement within the framework of the Prague morphological system is the 14th position of its positional tag.
Such description of aggregates could make use of the existing frame of the morphlological dictionary, without necessity to change the structure of the dictionary. On the other hand, the solution is less intuitive than the previous case of multiple lemmas and tags.
The morphological description of the examples presented above are given in the table 2. 3
Another problem of morphological tagging concerns different types of variants (sometimes called also mutations). There are stylistic variants, orthographic ones, historical etc. No matter what was the origin of the variant, it should be properly tagged as a variant. It is meaningful to join all the variants into a common dictionary record, but it must be done in such a way that does not disturbe the Golden rule of morphology.
The Golden rule of morphology (see [
There is a distinction between global variants (manifested in all wordforms of a paradigm) and inflectional ones (applied only for some combinations of morphological values). Until recently, this distinction was not taken into account consistently. For marking a wordform as a variant, the 15th position of the Prague tag was used. Both types of variants were marked in this way.
Inflectional variants are those variants that relate only to some wordforms of a paradigm defined by a particular combination of morphological values for the identical lemma. An example are two forms of the lemma hrad (castle) in local singular which can be both hradu and hradeˇ.
Global variants are those variants that relate to all wordforms of a paradigm, and always in the same way. The word lemon presented above is the example of the global variants.
For treatment of global variants, the lemmatization is very important. In this respect, the morphological dictionary has been inconsistent. Some global variants shared the same lemma, which violated the Golden rule of morphology, because the same morphological tag combined with that lemma was connected with two different wordforms. Others were lemmatized as distinct lemmas, which made impossible to link the variants. The lemma representing the both (or sometimes more) variants should link them, but at the same time, the Golden rule of morphology must not be violated. 3.1
In NovaMorf, the information about variants is added to
the morphological tag. Global variant as well as
inflectional variant became new (morphological) categories that
have a set of predefined values. The values are based
preferably on the orthographic features of individual
variants; they do not attempt to have any evaluative
meaning, such as expressive, vulgar, archaic or others.
Contrary to other morphological categories, there can be more
values of both variants. That is why a special notation
was proposed to express potentially more values of the
variants. No matter how the morphological tag is constructed
(Prague style [
All the global variants are then represented by a common lemma. Here again, the concept of multiple lemma is used. In the case of variants, its members have always the same POS – they are the variants themselves.
Table 3 shows an example of capturing the three global variants of the lemma thesis in NovaMorf.
The inflectional variants are tagged similarly; only instead the leading G, the letter F starts the sequense of the inflectional variants. Naturally, the inflectional variants need not to be represented by a multiple lemma. 3.2
In the PDT project, the inflectional variants are marked as before, at the 15th position of the tag. The list of possible values was substantially simplified; there are code numbers for marking literal and standard variants (1 – 5), and code numbers for substandard variants (6 – 9). No other finer distinction (archaic, colloquial etc.) is marked.
For annotating global variants, the concept of links, originally created for derivational relations4, was used. For every set of variants, it is necessary to choose one of them as a basic one. All the other global variants are then linked with that basic variant. A style marker is assigned to every link, but the set of its possible values is limited.
The selection of the basic variant is not crucial, because the set of links to other variants join them all, so that they can be reached all at once. However, it is reasonable to choose always the most common variant (in whatever sense).
The table 4 shows an example of capturing the three global variants of the lemma thesis in the PDT project. 4
We have presented and compared solutions of two problematic features occuring in Czech morphology, namely aggregates and variants. They were adopted by two different projects, PDT and NovaMorf, that are currently being finalized. The both projects used the same ideas, but implementations are different.
4The link connects the lemma under consideration to its derivational origin.
The NovaMorf project proposes to change some of the basics of the Prague tagging system. It wants to implement the concept of multiple lemma and use it for description of aggregates (sequence of segments of the aggregate) as well as for variants (set of lemma variants). The second change is creation of a subtag for marking variants (global and inflectional ones).
The PDT project is more traditional and does not introduce special formats. It is also the reason, why the changes described in this paper, have been already implemented to the new version of the morphological dictionary (however not publicly released yet) only within this project.
The treatment of aggregates is for the both projects equivalent. In NovaMorf, a special category (Type of Aggregate) was added for description of aggregates. Its value becomes a new part of the morphological tag. In PDT, the information about the type of the aggregate is incorporated into the existing positional tag. However, all the information about the aggregate, its type and its segments, are present in both solutions. NovaMorf treats them probably more transparently. The multiple lemma lists all the lemmas of the segments, while the mark within the morphlological tag (adopted by PDT) assumes that the users would derive the information about the segments from the mark, which is not so straightforward.
The treatment of variants is not equivalent in the two projects. NovaMorf is again more transparent — the concepts of multiple lemma and multiple tag will enable especially users of corpora not to take care about more possibilities, because the dictionary itself would know them all. Every variant is lemmatized by the same set of variant lemmas as shown in the example presented in the table 3. Individual lemmas (and wordforms) are then distinguished by the variant subtag, that uses a new set of values to mark the variants.
PDT, on the other hand, selects one variant as the basic one. Contrary to previous attempts, there is no predefined rule which variant to select. However, the authors insisted to preserve at least some information about the stylistic features of the individual variants. Lemma of each global variant is the variant itself.
If there was a need to unify the two solutions in the future, the lemma variants could be easily taken out from the dictionary and put together to make the set of a multiple lemma. The only thing that would need to add, would be the type of the variant according to the values prepared for NovaMorf. The opposite conversion, from multiple lemma to lemma variants would be even easier — each member of the set representing the multiple lemma would become an independent lemma. The selection of the central basic lemma for the link can be, as mentioned before, arbitrary. As the two approaches are not equivalent, there would be also needed some handwork, namely to add the information about the style of the variants.
The presented solutions could be possibly used also for other languages, but there were no attempts undertaken to prove it.
The research has been supported by the LINDAT/CLARIN and LINDAT/CLARIAH-CZ projects of Ministry of Education, Youth and Sports of the Czech Republic (LM2015071 and LM2018101). [9] Petkevicˇ, V., Hlavácˇová, J., Osolsobeˇ, K., Šimandl, J., Svášek, M.: Microsyntactic Parts of Speech in NovaMorf, a New Morphological Annotation of Czech. In: Proceedings of SLOVKO 2019, to appear.