Questionable relationship triples in the UMLS

The relationships of the UMLS Metathesaurus are used to describe the nature of the connections between pairs of concepts. The occurrence of multiple relationships between a given pair of concepts may be indicative of some kind of inconsistency. A methodology to algorithmically identify and then categorize all pairs of concepts with multiple relationships is presented. These potentially problematic concept pairs are grouped into four categories, including those that are possibly conflicting from a hierarchical standpoint and those that may violate a mutual-exclusion constraint. Samples of the identified concept pairs are reviewed. Some of the errors and inconsistencies found during the review are reported. The findings indicate that questionable UMLS relationship triples can be easily detected by algorithmic approaches, are common, and at times can be corrected in the UMLS itself.