Toward Constructing the National Cancer Institute Thesaurus Derived W ord N et (ncit WN ) (2018)

Abstract: We describe preliminary work in the creation of the first specialized vocabulary to be integrated into the Open Multilingual Wordnet (OMW). The NCIt Derived WordNet (ncitWN) is based on the National Cancer Institute Thesaurus (NCIt), a controlled biomedical terminology that includes formal class restrictions and English definitions developed by groups of clinicians and terminologists. The ncitWN is created by converting the NCIt to the WordNet Lexical Markup Framework and adding semantic types. We report the development of a prototype ncitWN and first steps towards integrating it into the OMW.

## introduction the global wordnet grid (gwg) is a platform created to join together wordnets by linking them to a central registry of concepts, using the collaborative interlingual index (cili) as a pivot. data in the gwg is linked following an 'onion model', with 'a core of concepts shared by many wordnets', validated by the community, and axiomatized through ontologies. the core extends to a middle layer with fewer shared wordnets and out to a layer of concepts mapped to only a single wordnet. an external layer contains synsets defined in project wordnets that do not fulfill the cili inclusion criteria. one of the advantages of the gwg is that the resource is no longer limited to networks of single-word units, but is now open to phrasenets (frequent adjective-noun, nounprep-noun, and verb-object combinations, as well as proverbs, idioms, and compounds). this feature creates the possibility to link wordnets to domainspecific terminologies, which often include multiword expressions. the open multilingual wordnet (omw) is the reference instantiation of the gwg @xcite adding the constraint that all member wordnets must be open according to the open definition. 1 to date no specialized terminologies have been included in the omw. consequently, there is no established procedure for mapping technical concepts to the cili nor for determining whether a technical concept ought to be indexed in the cili. we report a preliminary biomedical wordnet based on the national cancer institute thesaurus (ncit) called the ncit derived wordnet (ncitwn) and preliminary mappings to the cili. by mapping the ncit to the cili and thereby integrating it into the omw, we are developing the first specialized vocabulary mapped to the cili. the two outcomes will be: (i) the ncit mapped to the cili and integrated into omw, but just as significantly (ii) groundwork for a method to reliably integrate open and freely available specialized terminologies with these lexical resources. this work is a first step toward realizing the goals outlined in @xcite . ## results automatically generating candidate mappings based on lemma overlap and compatibility of umls semantic types with wordnet domaincategory types resulted in 47,464 candidates (out of 118,000), of which 6,028 had a match @xmath0.75: this means that either all lemmas overlap or else most lemmas overlap and the domains are compatible. an additional 10,454 matches had a score in the range .75 > .5. to date we have checked 570 of the 6,028 candidates with a match @xmath1.75. the results are summarized in in the manual analysis of pwn 3.0's coverage of the ncit, we found that 20.2% of the ncit concepts had an exact match in pwn (and therefore also the cili), 11.7% had no match in pwn, and 47.9% had a matching head noun, suggesting a suitable child concept of a synset in pwn. of the 19 top nodes in the ncit hierarchy, foot_3 three were exact matches and 11 had head nouns that were an exact match in pwn, suggesting a parent/child link. ## future work and discussion the coverage analysis and the initial evaluation of the match candidates have brought to light several concrete examples in which guidance is needed to integrate specialized terminologies with the cili. first, the ncit contains dot objects and other cases of systematic polysemy that are sometimes distinguished in wordnet and would therefore have different relevant concepts in the cili. for example, ncit cherry (c65311) does not have a proper definition but has two umls semantic types, fruit and plant, suggesting it can refer to a cherry tree or the fruit of a cherry tree. the candidate match in pwn is cherry n:2 (i103308) which is clearly defined as the tree, not the fruit. a matching strategy for such cases ought to be developed. second, we have encountered some cases where the core definition is the same, but exemplars or typical cases are different. in both examples below, an overlay is characterized as something to be applied over an object or surface. however, the ncit characterizes an overlay as typically for protection or identification and pwn considers an overlay to be decorative. it is unclear whether these are similar enough to be considered equivalent, whether the ncit concept should be considered a hypernym of the pwn synset (and therefore the corresponding cili concept), or whether the typical functions, though not a necessary component of the definition, nuance the meaning sufficiently for no hierarchy relation to be added between the two. third, we find that some concepts are probably equivalent, but different definition writing criteria result in a narrower definition in pwn. consequently, it is unclear whether the ncit concept is a hypernym of the pwn sysnet. finally, we need to decide how to handle multiword expressions that have been annotated with '2' such as breast cancer prognostic factor (c19601). one approach is to create a new concept in the cili. however, further consideration needs to be given to which concepts are too domain specific to be included in the cili. another approach is to map these to the cili by way of the head word using the hyponym relation. for example, breast cancer prognostic factor (c19601) would be mapped to i75200 by way of pwn factor. however, as the number of concepts in the cili grows, we anticipate that concepts that are not lexicalized in princeton wordnet will appear in the cili. for example, the concept prognostic factor may be added to the cili in the future. in the long term, strategies for detecting and properly aligning such concepts will need to be developed. we used umls semantic types, which were created to help disambiguate and cluster senses @xcite , to improve our automatic alignment to pwn coarse domains. pwn contains more detailed domain-category links such as tobacco n:1 is in the domain of pharmacy n:1 . we could exploit both them and the hypernyms to improve the automatic mapping. finally, if all the umls semantic types can be mapped to synsets, we can link them using domain-category. this will enrich the overall graph in ncitwn and facilitate mapping other umls terminologies to the cili.