Dictionaries are increasingly being transformed into linguistic linked lata (LLD) relying on the lemon and OntoLex models, but this conversion is not always straightforward. For both linked data (LD) based applications to exploit all content provided in dictionaries and lexicographers adopting LD technologies, the original data and structure should be retrievable from the LLD version to prevent any loss of information in the transformation. In this position statement we motivate the need for a new module in OntoLex targeted at the representation of dictionaries and which will address structures and annotations commonly found in lexicography. Some of the issues we identi ed in our initial experiences are presented as input for discussion, along with our initial approaches to solve them. Such a module is intended to be compatible with other modules in OntoLex and should guarantee information preservation, making LD a viable mechanism for lexicographers in the development of lexica.
Over the past few years, more and more e orts are being devoted towards the
conversion of dictionaries into Linguistic Linked Data (LLD), based on lemon [
Nonetheless, the conversion of a dictionary to OntoLex is not always straightforward. lemon was initially developed to enrich a given ontology with a lexical layer, and not with the idea of rendering any already existent dictionary to LLD. A majority of scholars working on this eld, however, are turning to lemon or OntoLex in pursuit of the latter objective. The more numerous and resource-speci c the annotations in a dictionary are, the more complex the modeling solutions are, especially if until then the dictionary was targeted at human users. We are aware that some solutions exceed the needs of lexical information that some NLP tools require. However, if we are also aiming to bring linked data to lexicography, all dictionary content must be taken into account and must be retrievable once converted to LLD, i.e, migrating to LLD should imply no information loss. This means that structural aspects of the dictionary, as for instance senses and homographs order, along with the sub-sense hierarchy some dictionaries display, should be kept in mind when o ering modeling solutions. There is a range of dictionary annotations (domain of usage, region, frequent use tags, restrictions on number and gender depending on a sense, etc.) that a ect word meaning and language usage and are not structural in nature. Collocations, idioms, paradigmatic relations, context indicators, semantic selection, among other aspects, are presented di erently in dictionaries and modeling them is not trivial.
The natural doubt that would be entertained by many experts is whether OntoLex is supposed to provide the means to model all aspects of a dictionary or whether this is outside of its scope, ontology lexicalization, and therefore should be tackled by another initiative. In this paper we motivate our insights on OntoLex to enable dictionary representation as LLD in all its granularity, and advocate for the creation of a lexicography-speci c module that would gather elements concerning dictionary structure and annotations. The module could also link to other potential modules that might be proposed, such as an etymologyoriented one to support etymological dictionaries, for instance.
The rest of the paper is organized as follows: Section 2 goes through the state of the art on LLD and lexicography and some of the problems encountered during the representation of dictionaries as LLD. Our motivation for OntoLex to be able to tackle those and the issues presented throughout the paper is stated in that section as well. Section 3 describes ve of a series of issues we identi ed in our work modeling and analyzing dictionary entries, and which we argue serve as input for discussion on the need for a module for lexicography. Our initial approaches towards such a module and a description of how it would solve the described issues are outlined in Section 4, while Section 5 o ers some concluding remarks. 2
There have been several reports in the literature on the conversion of
dictionaries to LLD, most of them relying on lemon or OntoLex. However, proprietary
formats, such as that of K Dictionaries (KD)7, often have XML tags used in
their annotation schemes that refer to linguistic categories or features which
are not present in available repositories of linguistic categories or which lack a
compatible de nition that prevents us from reusing the ontology entity at hand.
Ad hoc vocabularies were de ned to migrate content from the German
monolingual dictionary of KD's Global Series [
Structures typically found in dictionaries, such as the sense and sub-sense
hierarchy in an entry, are not trivial to model either. polyLemon [
The accurate representation of etymological information as LLD is key in
the conversion of historical and etymological dictionaries. An extension to lemon,
lemonet, to represent etymological information of lexical entries was proposed [
Alternatives to the use of OntoLex are available as well. The Oxford Global
Languages Ontology (OGL) [
In this position paper we do not focus on a particular kind of lexical
information present in dictionaries (e.g., etymology or morphology) but we aim
to highlight some di culties in the modeling of dictionary entries without
information loss. Thus, we will not target the representation of resource-speci c
features of particular dictionaries. Taken into account the problems reported
in the literature, and after analyzing dictionary entries in e-dictionaries of
English (Oxford [
We ground our proposal for a lexicography module on the following four points: (1) the use of OntoLex by the majority of the community to convert linguistic resources to LLD instead of to lexicalize ontologies, (2) the nature of lemon being descriptive but not prescriptive and the respect towards di erent lexicographic views, (3) the coming together of the lexicography and the Semantic Web communities and potential bene ts that LLD may bring about to lexicography, assuming it involves no information loss, and (4) the reuse of already available mechanisms in OntoLex. 3
In the following we report on some of the issues we have come across after our experiences in converting dictionaries to LLD and our analysis of dictionary entries in English, German and Spanish. Here we restrain ourselves to issues that reveal current limitations of the OntoLex model, i.e, cases in which applying the lemon core implies a di erent view on the data than the one provided in the original resource and, therefore, an information loss (type 1, hence T1), and missing entities, e.g. a property or a class, to account for information mostly found in dictionaries (type 2, hence T2). We have already raised some of these issues as input for discussion to the OntoLex community.9 9 https://www.w3.org/community/ontolex/wiki/Lexicography
Both lemon and OntoLex specify a lexical entry as a word, a multiword expression or an a x with a single part-of-speech, morphological pattern, etymology and set of senses.10 However, a headword in a dictionary may occur with di erent parts-of-speech depending on context and its senses are nonetheless de ned in the same dictionary entry, all of them derived from the same etymology (no homonymy involved). Applying the OntoLex model would imply the generation of several ontolex:LexicalEntr[ies], one per each part-of-speech the headword can take. Splitting the dictionary entry into several lexical entries would cause loss of information (shared etymology, pronunciation, senses implicitly related) and does not keep track of the dictionary representation. Examples: poison, bread, water (noun and verb), Sp. lento `slow, slowly' (adjective and adverb), Sp. alto `tall, loudly, height' (adjective, adverb and noun).
Some senses of a dictionary headword require a particular form, e.g. in English a plural form or in Spanish a masculine or feminine one. Since the meaning in these cases is associated with the form and it may di er signi cantly from other senses that do share gender or number features, splitting the dictionary entry into di erent lexical entries would be an option (see Issue 1). An alternative is the linking of that sense to elements in a catalog of grammatical categories which encode those grammatical restrictions, but we would need an exhaustive list of them in order for this option to be applicable. Examples: refreshment(s), Sp. cometa (m.) `comet', (f.) `kite'. In these cases, the dictionary entry can be a single one (e.g. refreshment in English or cometa in Spanish) but one of its senses indicates a preferred form. In the case of refreshment, the plural form is used if the intended meaning is snacks and beverages; with the Spanish cometa, the feminine form is applicable when referring to a kite, the masculine when denoting a comet. Further examples are good(s), manner(s); Sp. frente (m.) `front', (f.) `forehead'.
Usage examples of a word or multiword expression are often provided in the de nition of each of a dictionary entry's senses. Lexinfo includes a property lexinfo:senseExample to describe an example of a sense (as a subproperty of lemon:definition) and which is linked to the example data category in ISOCat.11 Nonetheless, due to it being a datatype property, it does not enable including further information on the example or to establish translation relations among examples, which is common practice in bilingual and multilingual dictionaries. The lemon model included a lemon:UsageExample class and a property lemon:example to link to it, but OntoLex does not cover this aspect yet. Exam10 https://www.w3.org/2016/05/ontolex/#lexical-entries 11 http://www.isocat.org/ ples: Sp. Preocuparse `worry'; Sp. no hay por que preocuparse `there is nothing to worry about' (Collins English-Spanish Dictionary).12
The order of senses may be based on frequency of use, date of origin, concreteness (from the most concrete to most abstract sense, etc.). Homographs are also given according to some ordering criteria that may vary from dictionary to dictionary. Their order should be searchable and retrievable as to recover the information provided in the original resource. Examples: Boa: noun. (1) any of a family (Boidae) of large snakes that kill by constriction and that includes the boa constrictor, anaconda, and python (2) a long u y scarf (Merriam Webster Dictionary)13; bat 1: n. 1. A stout wooden stick; a cudgel [. . . ]; bat 2: n. Any of various nocturnal ying mammals of the order Chiroptera [. . . ] (American Heritage Dictionary).14
Some dictionaries indicate the semantic features of the lexical items that an entry
(in one of its senses) selects or even the exact lexical items with which it
collocates. This is usually indicated either with a speci c tag (e.g. KD's tag Range Of
Application), or in-between parentheses at the beginning of a de nition.
Examples are, for instance, the dictionary entry for the German verb dammen, which
in its sense `to insulate, absorb, mute' selects arguments that denote warmth or
sound (German Warme, Schall, etc.) (KD)15, the adjective cozy, meaning
bene cial to all those involved and possibly somewhat corrupt if predicated from a
transaction or an arrangement (Google Dictionary)16; or the collocational
measure words of luck : stroke, piece of (Oxford Collocations Dictionary).17 The
synsem:OntoMap class allows to map a syntactic frame to an ontology entity,
so that the frame and its arguments are linked to the ontology elements that
they lexicalize. Even though dictionaries commonly include information on
subcategorization (transitive/intransitive/re exive etc. annotations for verbs, for
instance), details on the syntactic frame are not always provided beyond those
annotations. Since in dictionary conversion we often lack a given ontology and
detailed syntactic information is not provided, the mapping between
syntactic arguments and ontology entities seems di cult to establish automatically via
synsem:OntoMap: how do we automatically represent that the adjective cozy has
a meaning only applied to transaction or agreement or that the measure words
that collocate with luck are stroke, piece if the morphosyntactic information
provided in the dictionary is just that cozy is an adjective and luck a noun?
Furthermore, synsem:condition (in its turn subsuming synsem:propertyRange
and synsem:propertyDomain) enables us to state constraints on the arguments
of a predicate in a given ontology.18 The possibility of reusing it to state the
constraints on syntactic arguments even in cases in which we lack a given
ontology and therefore are not mapping to given ontology properties has to be
further analyzed. In addition, the potential links between the modeled entries
(e.g. piece and luck ) (i.e, the links at the lexical level) are also to be considered,
for instance, by taking into account recent proposals on the representation of
lexical functions as LLD [
The previous section dealt with some of the issues we encountered in our work with dictionaries and the potential ones that may rise with other lexicographic works that have not been migrated to LLD yet. In the following we draft a potential solution which can serve as basis for a new module in OntoLex speci cally developed for the representation of dictionaries after thorough revision and improvement according to the community's feedback.
In order to keep track of the dictionary representation and prevent any loss
of information mentioned in Issue 1, related to the splitting of dictionary entries
in several lexical entries, we propose a new class DictionaryEntry. This new
class would both enable to group together lexical entries as well as to associate
any information shared by all of them. A class Entry was proposed in the
recent Oxford Global Languages Ontology [
Regarding Issue 2, the DictionaryEntry class would allow to divide a single lexical entry into several ones if desired, each with a di erent preferred form, 18 https://www.w3.org/2016/05/ontolex/#conditions while maintaining the original dictionary representation. If the dictionary entry is not split, the option of linking a sense to a grammatical restriction on gender or number from an external catalog would solve the issue, although the implications of this solution (its bene ts and drawbacks) will need further analysis.
In order to represent usage examples and their translations (Issue 3) we propose to go back to lemon:UsageExample and link it to a LexicalSense. A new class ExampleCluster would link to UsageExamples that are translations from each other. The use of the vartrans module to model translations among senses would imply the creation of lexical senses for each example, and therefore treating the example as a lexical entry, which we deem is beyond the de nition of lexical entries.
Issue 4 was concerned with the order of senses in a dictionary entry and the order of homographs in the macrostructure of the dictionary. There are di erent possible approaches to resolve this: reusing already available RDF mechanisms, reifying the sense order in a new class SenseOrder, or de ning a new property senseOrder attached to the lexical sense. The rst and straightest forward option involves the reuse of rdfs:Containers to declare with e.g. rdf: 1, rdf: 2 that a particular sense is the rst or the second one. However, cases in which a set of senses allows for various orderings, depending on the ordering criterion, or in which some senses come from di erent dictionaries (each one with its order), should also be accounted for.
The second option suggests that the sense order is rei ed in a class SenseOrder linked to the lexical sense. This class would enable us to record the position of that sense, its provenance (presumably an instance of the class Dictionary), and, if desired, the ordering criterion. If repeated senses were identi ed (e.g. senses that share a de nition in both dictionaries), SenseOrder would allow us to have one single lexical sense with two di erent positions according to the two di erent orderings and dictionaries, in a similar fashion as two containers with two di erent sequences of senses. Alternatively, if we assume that a lexical sense always comes from just one dictionary source, a property senseOrder would su ce.
Issue 5, dealing with semantic selection, has been brought up for further
discussion in this paper as to see whether it could be covered by synsem module
mechanisms or whether it would require new entities in the context of the
lexicography module. As part of the conversion of the KD's Global Series Spanish
Multilingual Dictionary [
OntoLex is increasingly being used to convert linguistic resources to LLD outside the scope of ontology localization. In this position statement we have drawn attention to a series of issues raised in the literature on LLD related to the conversion of dictionaries to LD and to ve of the ones we came across in the same line of work and after a later analysis of several additional dictionaries. We argue that the OntoLex model should enable the preservation of the content and the structure of the original resource, even if the LLD expert opts for a di erent representation more suited to the exploitation of the data by external applications or more in line with his or her view on the lexicon-ontology interface. We have outlined some of our insights on how to address these issues in a new module for lexicography. It would be compatible with the mechanisms suggested in the state-of-the art on dictionaries in LLD, as of the moment of writing, and also with other potential modules for the representation of speci c lexical aspects (e.g. etymology). The nal module is intended to be dictionary-agnostic in the sense that it should be applicable (and combined with other modules if necessary) to di erent kinds of dictionaries (e.g., general, collocations, learner's, etymological, historical, etc.). This would bring linked data (LD) closer to lexicography not only with the aim of leveraging already available dictionaries in LD for NLP tasks, but also of introducing linked data in the work carried out in that discipline.
Acknowledgments. We thank the anonymous reviewers for their insightful suggestions that have contributed to the improvement of this article. This work is supported by the Spanish Ministry of Education, Culture and Sports through the Formacion del Profesorado Universitario (FPU) program, and by the Spanish Ministry of Economy and Competitiveness through the project 4V (TIN201346238-C4-2-R) with the FEDER funding scheme, the Juan de la Cierva program, and the Excellence Network ReTeLe (TIN2015-68955-REDT).