The OntoLex vocabulary has been designed to capture lexicons and to add their lexicographical knowledge to ontologies in the Semantic Web. Although the speci cation of the vocabulary posits that OntoLex allows lexicons to be ordered onomasiologically, it does so for a very speci c kind of onomasiological ordering only. As a consequence, the vocabulary is currently insu cient for capturing a large proportion of the existing topical thesauri. This paper demonstrates the current expressivity and this shortcoming of OntoLex through two case studies: The Historical Thesaurus of the Oxford English Dictionary and The Scots Thesaurus. In order for OntoLex to o er full support for topical thesauri and their ordering principles, this paper proposes the addition of a single property to the vocabulary: ontolex:isSenseIn. . . .
The Lexicon Model for Ontologies vocabulary has been designed to capture
lexicons and to add their lexicographical knowledge to ontologies in the Semantic
Web [
The speci cation of OntoLex puts forward a manner in which \lexicons can be
ordered onomasiologically, that is by meanings rather than by lemmas" [
In order to provide insight into the current support of OntoLex for the
onomasiological ordering of topical thesauri, this paper will present two case
studies. The rst is based on the Historical Thesaurus of the Oxford English
Dictionary [
This paper expresses samples from both thesauri in the OntoLex vocabulary.
The manner in which OntoLex is applied is in line with the speci cation of the
vocabulary [
Listing 1. Namespaces @prefix ontolex: <http://www.w3.org/ns/lemon/ontolex#> . @prefix owl: <http://www.w3.org/2002/07/owl#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . @prefix skos: <http://www.w3.org/2004/02/skos/core#> . @prefix wn: <http://wordnet-rdf.princeton.edu/ontology#> . 3
Case study Historical Thesaurus of the OED
The rst case study presented here is that of the Historical Thesaurus of the
Oxford English Dictionary (HTOED). HTOED captures the English lexis that
has existed throughout its 1300-year history, from Old English up to Modern
English. This topical thesaurus groups together lexical items that are considered
near-synonymous and provides insight into their use in time and place. HTOED
was rst published in print in 2009 [
Society Communication
Authority
Lack of subjection Permission
Freedom/liberty synonyms freedom, n. y freeship, n. y franchise, n.
liberty, n. ...
(in sense 3) (in sense 2) (in sense 1a) (in sense 1b of homonym 1)
Expressing categories of the topical system of HTOED in OntoLex is
relatively straightforward. Each HTOED category corresponds with a lexical
concept in OntoLex. The latter is de ned as a \mental abstraction, concept or
unit of thought that can be lexicalized by a given collection of senses" [
Listing 2. HTOED category \Freedom/liberty" expressed in OntoLex <category-FreedomLiberty> a ontolex:LexicalConcept ; skos:prefLabel "Freedom/liberty"@en ; skos:broader <category-LackOfSubjection> .
The OntoLex vocabulary also contains terminology to express lexical senses
and the lexical entries to which they belong. In order to state that a given
lexical sense from HTOED belongs to one of its categories, the property
ontolex:isLexicalizedSenseOf can be used. This property relates a lexical
sense to a lexical concept, stating that it \lexicalizes" that concept. According
to the section on Lexical Nets in the OntoLex speci cation, lexical senses that
lexicalize the same concept are considered synonymous [
Listing 3. HTOED sense of freedom expressed in OntoLex <sense-freedom-n-3> a ontolex:LexicalSense ; skos:prefLabel "freedom n. (sense 3)"@en ; ontolex:isSenseOf <entry-freedom-n> ; ontolex:isLexicalizedSenseOf <category-FreedomLiberty> . <entry-freedom-n> a ontolex:LexicalEntry ; skos:prefLabel "freedom, n."@en ; wn:partOfSpeech wn:noun .
As shown, capturing the onomasiological ordering of the HTOED lexicon presents no issues with the OntoLex vocabulary. The vocabulary enables one to express categories and their hierarchy, lexical senses and their relation to a lexical entry, and the relation between the senses from HTOED and the categories to which they belong. 4
Case study The Scots Thesaurus
The second case study in this paper concerns The Scots Thesaurus (ScT) [
Farming Farmers
Crops Ploughing
Sowing y blander (in sense 'disperse scantily') happer (in sense 'a basket or container') heuch (in sense 'earth up plants in drills') miss (in sense 'fail to germinate or grow') ...
Fig. 2. Example ScT content
Expressing categories from ScT is possible in a manner identical to that used for HTOED. The result for the \Sowing" category from ScT, including its relation to the superordinate category \Crops", is provided in Listing 4.
Listing 4. ScT category \Sowing" expressed in OntoLex <category-Sowing> a ontolex:LexicalConcept ; skos:prefLabel "Sowing"@en ; skos:broader <category-Crops> .
As for the lexical senses from ScT, these too can be expressed in OntoLex comparable to how it has been done for HTOED. There is, however, a notable di erence. The property ontolex:isLexicalizedSenseOf is unsuitable for relating the senses of ScT to the categories to which they belong. The lexical senses in ScT are not necessarily lexicalizations of the category in question. Moreover, senses that belong to the same category are not necessarily considered synonymous. In fact, they rarely are. A case in point are the senses of happer and miss from the sample. Both of these senses are members of the category \Sowing", and indeed belong to that semantic domain, but can hardly be said to be synonymous or even to lexicalize the category.
What is missing, then, from the OntoLex vocabulary is terminology to express a looser manner of onomasiological ordering with categories than ontolex:isLexicalizedSenseOf does. The RDF snippet in Listing 5 contains the desired situation, where a tentative property isSenseIn is coined (see highlighted line) to express the relation between the sense of blander and the category to which it belongs.
Listing 5. ScT sense of blander expressed in OntoLex <sense-blander-v-disperseScantily> a ontolex:LexicalSense ; skos:prefLabel "blander"@sco ; skos:definition "disperse scantily"@en ; ontolex:isSenseOf <entry-blander-v> ; :isSenseIn <category-Sowing> . <entry-blander-v> a ontolex:LexicalEntry ; skos:prefLabel "blander, v."@sco ; wn:partOfSpeech wn:noun .
In short, OntoLex itself does not yet provide terminology to onomasiologically order the lexicographical content of ScT { and of other thesauri like it. 5
The two case studies have shown that OntoLex is not yet expressive enough to indicate the relation between senses and categories for all topical thesauri. In fact, the lack of a property like the tentative isSenseIn does not just a ect conveying content from ScT and the great many existing cumulative thesauri like it. It also a ects expressing these very relations found in thesauri such as HTOED. After all, senses in HTOED are not just lexicalizations of a category, they are also members of a number of categories. To illustrate, the assertion that the HTOED sense of freedom is a lexicalization of the category \Freedom/liberty" entails that this sense is a member of not just that category but also of its superordinate categories (see Listing 6).
Listing 6. HTOED sense of freedom and its relation to the categories of HTOED <sense-freedom-n-3> a ontolex:LexicalSense ; ontolex:isLexicalizedSenseOf <category-FreedomLiberty> ; :isSenseIn <category-FreedomLiberty> , <category-LackOfSubjection> , <category-Authority> , <category-Society> .
In order to truly express how senses are categorized according to topical systems in thesauri, then, additional terminology is required beyond what OntoLex currently o ers. Properties from other vocabularies that might ll the gap, such as the subject property from Dublin Core Terms [11], tend to be too generic to be able to infer further knowledge from topical systems of thesauri. Moreover, the relation between such properties and ontolex:isLexicalizedSenseOf is not evident. As such, the required terminology is best captured in an update of the OntoLex vocabulary itself. The small addition of a single property such as isSenseIn (see Listing 7), then, and asserting its connection to the existing OntoLex property (see Listing 8) would enable onomasiological ordering of lexicons in topical thesauri of all varieties { distinctive or cumulative, and regardless of whether synonymy is indicated between senses.
Listing 7. Suggested OntoLex property isSenseIn ontolex:isSenseIn a owl:ObjectProperty ; rdfs:label "is sense in"@en ; rdfs:comment "This property relates a lexical sense to a concept that captures its meaning to some extent (that is, partially or even fully)."@en ; rdfs:domain ontolex:LexicalSense ; rdfs:range ontolex:LexicalConcept .
Listing 8. Connection between existing OntoLex property and the suggested one ontolex:isLexicalizedSenseOf
rdfs:subPropertyOf ontolex:isSenseIn . 6
This paper has shown, by means of two case studies, to what extent the OntoLex vocabulary currently supports relating lexical senses to the concepts that facilitate an onomasiological ordering. Such an ordering is (by their very de nition) used in lexicographical works known as topical thesauri. As it stands, the OntoLex vocabulary o ers some support for those thesauri considered to be distinctive and that capture synonymy. Such thesauri ensure that lexical senses displayed at a certain category do not just belong to that category, but also express (or lexicalize) that category. Those thesauri that do not have that same level of speci city, but merely use their categories to organize lexical senses into semantic domains, are not yet supported by the terminology in OntoLex.
The small addition of a single property, as suggested in this paper, would have a big impact on the expressivity of OntoLex. The onomasiological ordering of both distinctive and cumulative thesauri { regardless of whether these thesauri indicate synonymy { could then properly be conveyed on the Semantic Web. As a result, the variety of lexicographical resources that sit comfortably in OntoLex would not be limited to dictionaries and lexical nets, as is presently the case, but would also include thesauri. Increased support in OntoLex for onomasiological ordering, then, would allow all these resources to truly shine on the Web. In short, ordering by meaning through the new ontolex:isSenseIn is both meaningful and sensible.