# An Interoperable UMLS Terminology Service Using FHIR
## 3 Background
### Comparing UMLS Knowledge Structure and FHIR ConceptMap
#### 3.3.2 Differences  
* The ConceptMap cannot capture the label attribute of the relationship (Relationship class, Figure 3). For example, Atrial Fibrillation (source with CUI C0004238) is related to Digoxin (target with CUI C0012265), where the attribute's type has the value related, and the label has the value may_be_treated_by. * As mentioned previously, the equivalence attribute of TargetElement in ConceptMap is bound up with ConceptMapEquivalence valueset, and the values of the valueset describe the nature of the mapping between SourceElement and TargetElement. The equivalence attribute of the TargetElement class can be mapped to the type attribute of the UMLS relationship (Relationship class, Figure 3). A relationship type attribute can only take a value from the UMLS REL set. The mapping between the ConceptMapEquivalence valueset's values and the REL set's values is not exactly one to one. There is one to one mapping between a few values across the sets without loss of semantics, but for some values, there is no mapping. The lack of the mapping is either due to the unavailability of an equivalent value in the other set, or the fact that the official description of the value, particularly the values in the UMLS REL set, is vague, making it hard to determine a mapping. For example,
* The value PAR or CHD (representing hierarchy between UMLS concepts) from the REL set has an equivalent mapping to Subsumes or Specializes in ConceptMapEquivalence;
* The values AQ or QB or Empty from the REL set do not map to any value in the ConceptMapEquivalence valueset;
* The value RU in the UMLS REL set, described as \"Related, unspecified\", is not clear, making it hard to determine a mapping to ConceptMapEquivalence values, and is hence unmapped. * ConceptMap cannot capture the semantic type of a concept or atom. Table 1 summarizes this discussion. The content of the table is formatted in *.attribute format, where * indicates the class name. For example, Concept.CUI (Figure 3) refers to the CUI attribute of the Concept class and ConceptMap.Group.target refers to the target attribute of the Group class in the class ConceptMap. Table 2 shows the values mapped (and unmapped) between REL set and ConceptMapEquivalence valueset, along with the value definition/description from the sources. \begin{table}
\begin{tabular}{c c} \hline \hline
**UMLS Knowledge Structure** & **FHIR ConceptMap** \\ (Figure 3) & **(Figure 4)** \\ \hline Concept.CUI & ConceptMap.Group.SourceElement.code \\ \hline Concept.name & ConceptMap.Group.SourceElement.display \\ \hline Concept.semanticType & — \\ \hline Atom.AUI & ConceptMap.Group.TargetElement.code \\ \hline Atom.name & ConceptMap.Group.TargetElement.display \\ \hline Mapping of atoms to a CUI (mapped\_to) & ConceptMap.Group.TargetElement.equivalence \\ \hline Relationship.type (Relationship between CUI) & — \\ \hline Relationship.label & — \\ \hline Source.name & — \\ (Source standard) & — \\ \hline Source.uri & ConceptMap.Group.target \\ \hline Source.version & ConceptMap.Group.targetVersion \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mapping between UMLS Knowledge Structure and ConceptMap.