Ontologies for historical languages: using the L i L a and O nto L ex- L emon framework to build a Lemma Bank for O ld I rish (2025)

Abstract: This paper presents a Linked Data approach to digitising and structuring Old Irish linguistic resources using the Lila (Linking Latin) ontology, which is itself largely based on the OntoLex-Lemon framework (Cimiano et al., 2016). Old Irish, as an ancient Celtic language with fragmented textual traditions, presents unique challenges for the creation and interoperability of digital resources. This work is part of the MOLOR project, whose aim is to create a knowledge base for Old Irish by interlinking texts, lexicons, and inflectional data. The first step in this ambitious endeavour is described here: the creation of an RDF linguistic Linked Data hub known as a Lemma Bank, similar to the one created as part of the LiLa project, addressing specific linguistic challenges and opportunities while adhering to the LiLa ontology.

## introduction the digitisation of ancient and medieval languages presents significant challenges for computational linguistics and digital humanities scholars. old irish (600-900 ce) constitutes the earliest attested period of the irish language-and of any celtic language-for which the surviving documentary evidence is sufficiently comprehensive to allow a complete synchronic linguistic analysis; it is important for both the study of indo-european linguistics and later stages of the irish language @xcite . however, the combination of morphological complexity and orthographic variation (see section 2.2), along with the use of different editorial standards, annotation schemas, and data formats in linguistic resources, creates substantial barriers to the successful use of standard natural language processing (nlp) methods @xcite @xcite . these factors also hinder resource compatibility and interoperability @xcite . the most important challenge in the current work is the variation seen in lemmatisation practice across lexical resources, particularly with regard to inflectional categorisation (see section 4.1). recent advances in linked data technologies and semantic web frameworks offer promising solutions to address these challenges. the lila (linking latin) ontology, originally developed for latin linguistic resources, provides a robust framework for representing ancient and historical language data in machine-readable formats that support interoperability and scholarly research @xcite . this paper describes the implementation of the lila ontology-in turn adhering to ontolex-lemon-in the context of the old irish molor project foot_0 , presenting both methodological approaches and practical solutions to the unique challenges posed by this medieval celtic language. the work contributes to the growing field of digital resources for ancient languages while demonstrating the adaptability of existing ontological frameworks to new linguistic contexts. the lila project foot_2 @xcite represents a particularly relevant model, creating a comprehensive linked data ecosystem for latin linguistic resources. lila's ontology provides sophisticated mechanisms for representing morphological, syntactic, and semantic information while maintaining interoperability across diverse resource types and scholarly traditions. these projects demonstrate the feasibility and scholarly value of linked data approaches for historical language materials, enhancing discoverability, interoperability, and analytical capabilities. ## modelling: the lila lemma ontology the lila ontology provides a comprehensive framework for representing linguistic data through linked data principles. the lila knowledge base centres on a comprehensive collection of latin lemmas that serve as connection points between different language resources. since the system is vocabulary-focused, these lemmas link together dictionary entries, corpus texts and nlp output that reference the 'common denominator', enabling seamless integration across resources @xcite . the ontology incorporates multiple levels of linguistic analysis, from graphemic representation through morphological, lexical, and syntactic annotation to semantic and pragmatic information. the ontology employs standardised vocabularies and uri schemes that enable cross-referencing between different resources and projects, supporting both human-readable scholarly annotation and machine-processable data that can be queried and analysed computationally. the lila lemma ontology is described and exemplified in listing 1: lila lemma class definition lila:lemma a rdfs:class, owl:class ; rdfs:comment "a lemma must have a pos, but it cannot have more than 1", "in lila, a lemma is a form in the word inflection that is used (or may potentially be used) to lemmatize tokens in a corpus." ; rdfs:label "lemma" ; rdfs:subclassof ontolex:form ; rdfs:subclassof [ a owl:restriction ; owl:onclass lila:pos ; owl:onproperty lila:haspos ; owl:qualifiedcardinality "1"^^xsd:nonnegativeinteger ] . listing 2: the entry sequor 'to follow' as modelled according to the lila lemma @xmath0:lemma ; rdfs:label "sequor" ; lila:@xmath1; lila:hasinflectiontype lila:v3d ; lila:haspos lila:verb ; lila:@xmath2; dcterms:@xmath3; ontolex:writtenrep "sequor"@la , "secor"@la . listings 1 and 2, respectively. although a discussion on the application of lila and ontolex-lemon classes and properties to old irish lexemes has already been provided in @xcite , it might be prudent to briefly explain the lila:lemmavariant property here again. this property was created in lila to cater for the use of alternative canonical forms used for the same lexeme as represented in lexical entries while at the same time maintaining resource interoperability. consider figure 1 . here we see four inflectional variants-first vs second conjugation, active vs deponent-representing four citation forms for the same latin lexeme 'to limp'. using the commutative property lemmavariant, "lila harmonises different lemmatisation strategies and annotation styles, thus granting interoperability" @xcite . this is exactly because each resource or token linked to one of those lemmas is linked to any other token or resource lemmatised using one of the variant lemmas. note that this elegantly circumvents the restriction that an ontolex:lexicalentry can have at most one canonical form @xcite . for purely orthographic variation (or certain phonological variants in the case of old irish @xcite ), the different spellings are modelled according to the more general property representation (ontolex:writtenrep) and, crucially, as part of the same lemma and hence uri-compare the written variants sequor and secor in listing 2 and claudo and cludo in figure 1 , respectively. for the old irish implementation, lila's core concepts have been adhered to-not without challenges-as detailed in section 4.1. ## conclusion and future work the current work has focused on building an rdf lemma bank for old irish to interconnect linguistic resources according to semantic web principles and the lila ontology in particular. the application of the lila ontology to old irish demonstrates both the potential and challenges of existing linked data frameworks for under-resourced ancient and historical languages. a clear-cut mapping to lila lemma properties is not always trivial due to morphological and orthographic variation, inconsistency, or different resolution in in-flectional annotation (to which we can add uncertainty originating in gaps in attestation). the decision was made not to enforce a single, harmonised morphological annotation system within the lemma bank, but instead to leverage the lila:lemmavariant property (currently without using lila:hasinflectiontype) to interlink alternative lemmas and ontolex:writtenrep for orthographic variation, thus respecting the distributed nature of linked data. the lemma bank is expected to grow in size (more lemmas and more pos categories), with the linking of resources to the lemma bank constituting the beginnings of a knowledge base for old irish, with sparql endpoints that support complex morphological and syntactic searches throughout the old irish corpus. 11 such a knowledge base will hopefully lead to enhanced search and analysis capabilities, while also highlighting areas where traditional philological approaches remain necessary supplements to computational methods. user feedback from the scholarly community will be the best measure of project success; the author hopes to report on use cases during a future edition of the ontolex workshop series. this verbal noun has a gen.sg in -e and as such does not fully adhere to i-stem inflection, even though this stem designation may be etymologically correct; see @xcite on the blurred lines between ā-and i-stem inflection with certain verbal nouns.