Semantic Web 0 (0) 1 1 IOS Press OLiA – Ontologies of Linguistic Annotation Editor(s): Sebastian Hellmann, AKSW, University of Leipzig, Germany; Steven Moran, LMU Munich, Germany; Martin Brümmer, AKSW, University of Leipzig, Germany; John P. McCrae, CITEC, Bielefeld University, Germany Solicited review(s): Menzo Windhouwer, Max Planck Institute for Psycholinguistics, Nijmegen, The Netherlands; Steve Cassidy, Macquarie University, Sydney, Australia; one anonymous reviewer Christian Chiarcos ∗ and Maria Sukhareva Applied Computational Linguistics (ACoLi), Department of Computer Science and Mathematics, Goethe-University Frankfurt am Main, Germany, http://acoli.cs.uni-frankfurt.de Abstract. This paper describes the Ontologies of Linguistic Annotation (OLiA) as one of the data sets currently available as part of Linguistic Linked Open Data (LLOD) cloud. Within the LLOD cloud, the OLiA ontologies serve as a reference hub for annotation terminology for linguistic phenomena on a great band-width of languages, they have been used to facilitate interoperability and information integration of linguistic annotations in corpora, NLP pipelines, and lexical-semantic resources and mediate their linking with multiple community-maintained terminology repositories. Keywords: linguistic terminology, grammatical categories, annotation schemes, corpora, NLP, tag sets, interoperability 1. Background repositories have converged into a generally accepted repository of reference terminology: They introduce The heterogeneity of linguistic annotations has been an intermediate level of representation between ISO- recognized as a key problem limiting the interoper- cat, GOLD and other repositories of linguistic refer- ability and reusability of NLP tools and linguistic data ence terminology and are interconnected with these re- collections. Several repositories of linguistic annota- sources, and they provide not only means to formalize tion terminology have been developed to facilitate an- reference categories, but also annotation schemes, and notation interoperability by means of a joint level of the way that these are linked with reference categories. representation, or an ‘interlingua’, the most prominent probably being the General Ontology of Linguistic De- scription [12, GOLD] and the ISO TC37/SC4 Data 2. Architecture Category Registry [21, ISOcat]. Still, these repositories are developed by different The Ontologies of Linguistic Annotations [3] rep- communities, and are thus not always compatible with resent a modular architecture of OWL2/DL ontolo- each other, neither with respect to definitions nor tech- gies that formalize the mapping between annotations, nologies (e.g., there is no commonly agreed formalism a ‘Reference Model’ and existing terminology reposi- to link linguistic annotations to terminology reposito- tories (‘External Reference Models’). ries). The OLiA ontologies were developed as part of an The Ontologies of Linguistic Annotation (OLiA) infrastructure for the sustainable maintenance of lin- have been developed to facilitate the development of guistic resources [28], and their primary fields of appli- applications that take benefit of a well-defined termi- cation include the formalization of annotation schemes nological backbone even before the GOLD and ISOcat and concept-based querying over heterogeneously an- notated corpora [16,10]. *Corresponding author. E-mail: [email protected] In the OLiA architecture, four different types of on- frankfurt.de tologies are distinguished (cf. Fig. 1 for an example): 1570-0844/0-1900/$27.50 c 0 – IOS Press and the authors. All rights reserved 2 Chiarcos and Sukhareva / OLiA – Ontologies of Linguistic Annotation – The OLIAREFERENCE MODEL specifies the tions (coreference, discourse relations, discourse struc- common terminology that different annotation ture and information structure). Annotations for lexi- schemes can refer to. It is derived from existing cal semantics are only covered to the extent that they repositories of annotation terminology and ex- are found in syntactic and morphosyntactic annotation tended in accordance with the annotation schemes schemes. Other aspects of lexical semantics are be- that it was applied to. yond the scope of OLiA: Existing reference resources – Multiple OLIAANNOTATION MODELs formal- for lexical semantics available in RDF include Word- ize annotation schemes and tagsets. Annotation Net, VerbNet and FrameNet, their linking with OLiA is Models are based on the original documentation, recommended as part of the lexicon model lemon [22], so that they provide an interpretation-independent and has been implemented, for example, in lemonUby representation of the annotation scheme. [11]. – For every Annotation Model, a LINKING MODEL Since their first presentation [3], the OLiA ontolo- defines v relationships between concepts/proper- gies have been continuously extended. At the time of ties in the respective Annotation Model and the writing, the OLiA Reference Model distinguishes 280 Reference Model. Linking Models are interpreta- MorphosyntacticCategorys (word classes), 68 tions of Annotation Model concepts and proper- SyntacticCategorys (phrase labels), 18 Mor- ties in terms of the Reference Model. phologicalCategorys (morphemes), 7 Mor- – Existing terminology repositories can be inte- phologicalProcesses, and 405 different values grated as EXTERNAL REFERENCE MODELs, if for 18 MorphosyntacticFeatures, 5 Syntac- they are represented in OWL2/DL. Then, Link- ticFeatures and 6 SemanticFeatures (for ing Models specify v relationships between Ref- glosses, part-of-speech annotation and for edge labels erence Model concepts and External Reference in syntax annotation). Model concepts. As for morphological, morphosyntactic and syntac- tic annotations, the OLiA ontologies include 32 An- The OLiA Reference Model specifies classes for lin- notation Models for about 70 different languages, in- guistic categories (e.g., olia:Determiner) and cluding several multi-lingual annotation schemes, e.g., grammatical features (e.g., olia:Accusative), as EAGLES [3] for 11 Western European languages, well as properties that define relations between these and MULTEXT/East [8] for 15 (mostly) Eastern Eu- (e.g., olia:hasCase). ropean languages. As for non-(Indo-)European lan- Conceptually, Annotation Models differ from the guages, the OLiA ontologies include morphosyntac- Reference Model in that they include not only concepts tic annotation schemes for languages of the Indian and properties, but also individuals: Individuals rep- subcontinent, for Arabic, Basque, Chinese, Estonian, resent concrete tags, while classes represent abstract Finnish, Hausa, Hungarian and Turkish, as well as concepts similar to those of the Reference Model. Fig- multi-lingual schemes applied to languages of Africa, ure 1 gives an example for the individual PDAT from the Americas, the Pacific and Australia. The OLiA on- the STTS Annotation Model, the corresponding STTS tologies also cover historical varieties, including Old concepts, and their linking with Reference Model con- High German, Old Norse and Old Tibetan. Addition- cepts. Taken together, these allow to interpret the indi- ally, 7 Annotation Models for different resources with vidual (and the part-of-speech tag it represents) as an discourse annotations have been developed. olia:Determiner, etc. External reference models currently linked to the OLiA Reference Model include GOLD [3], the Onto- Tag ontologies [1], an ontological remodeling of ISO- 3. Data Set Description cat [4], and the Typological Database System (TDS) ontologies [26]. From these, only the TDS ontolo- The OLiA ontologies are available from http:// gies are currently available under an open (CC-BY) purl.org/olia under a Creative Commons Attri- license,1 but these take a focus on typological data bution license (CC-BY). bases rather than NLP and annotation interoperability. The OLiA ontologies cover different grammatical phenomena, including inflectional morphology, word classes, phrase and edge labels of different syntax an- 1http://languagelink.let.uu.nl/tds/ notations, as well as prototypes for discourse annota- ontology/LinguisticOntology.owl Chiarcos and Sukhareva / OLiA – Ontologies of Linguistic Annotation 3 GOLD and ISOcat should be available under an open ability between GOLD and ISOcat (that – despite on- license,2 but can currently not be redistributed because going harmonization efforts [20] – are maintained by of an uncertain licensing situation (no explicit license different communities and developed independently). information). The OntoTag ontologies are available to Using the OLiA Reference Model, it is thus possible to the author but have not been publicly released. develop applications that are interoperable in terms of In this context, the function of the OLiA Reference GOLD and ISOcat even though both are still under de- Model is not to provide a novel and independent view velopment and both differ in their conceptualizations. on linguistic terminology, but rather to serve as a sta- Such applications are briefly described in the follow- ble intermediate representation between (ontological ing section. models of) annotation schemes and these terminology repositories. This allows any concept that can be ex- pressed in terms of the OLiA Reference Model also 4. Application to be interpreted in the context of ISOcat, GOLD, On- toTag or TDS. OLiA serves to aggregate annotation Initially, the OLiA ontologies have been intended to terminology as found in linguistic resources