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160 Osborne et al.Fig. 3. Querying the UMLSKS. The UMLSKS can also be installed locally.with less difficulty. The webpage for the UMLS users groups is located athttps://list.nih.gov/archives/umlsusers-l.html.3.2. Using a Custom Data SourceMMTx has three different models for candidate retrieval from Metathesaurusthat differ in extent of filtering applied. However, most users should be satisfiedusing these models, in some cases a user may need to create a custom data set. Atypical use case might be for commercial applications using the Metathesaurusthat must exclude particular vocabularies owing to licensing restrictions. Using acustom data will require that both the UMLS Metathesaurus and Metamorphosysbe downloaded and installed.It should be kept in mind that a custom data set is not required to restrict resultsto appropriate concepts. Whereas creating a custom data source does give the userthe ability to prevent matches to unsuitable concepts, a postmatch filtering can stillbe done to eliminate unwanted concepts from particular vocabularies or semantictypes. A custom data source is generally only warranted to avoid licensing problemsor if the information to be extracted from the input data cannot easily bedescribed by the UMLS semantic network or particular vocabularies. Because ofthe release of MMTx 2.4.B, candidate concepts can be filtered by both semantictype and by vocabulary from command line of MMTx, making custom data setsless critical. It is advised against creating a custom data set if the concepts of interestare small in number, they can be described by particular vocabularies, or if theyare restricted to certain semantic network types. The custom data set can alwaysbe created later. The creation of a custom data set will not be covered herein, butfor those who are interested in the details on custom data sets creation, the informationcan be found at http://mmtx.nlm.nih.gov/DataFileBuilder.pdf.