## 3 Results
### Construction of the Small Ontology  
First, the new basic file was analysed by looking at PDFs with identical combinations of the values for each of their descriptors and characteristics. This analysis was repeated with different sets of descriptors and characteristics. In Table 1, the results in terms of number of unique combinations are given for the different sets of descriptors and characteristics, including the new characteristic SYS for systemic effect. When all descriptors and characteristics were taken into account (Analysis 1), 383 unique combinations were observed. This indicates that the descriptors and characteristics are not completely definitional (given the 428 dose forms in the EDQM terminology; see Supplementary File/List7-Analysis1). Analysis 2 (357 unique combinations) may reflect a granularity that is closer to the granularity of Snomed-CT, although Snomed-CT focusses on manufactured dose forms, rather than on administrable dose forms (see Supplementary File/List8/Analysis2). Analysis 3 (based on only the four characteristics) results in a much lower granularity (206 unique combinations), unsuitable for granular identification of dose forms, but used for the further elaboration of the ontology (see Supplementary File/List7-Analysis-1; see Supplementary File/List9-Analysis3). Analysis 4 (195 unique combinations) was based only on the basic dose form of the administrable dose form and three characteristics (release characteristics, intended site, method of administration; see Supplementary File/List10-Analysis4). In analysis 4 bis, the same set is used as in analysis 4, without the new variable SYS, hence, only using basic dose form of the administrable dose form, RC, ISIC-split, and AMEC. This mimics the approach used in the FDA/WHO_UMC pilot project to explore the generation of a global identification number [7; 9], and resulted in a granularity closer to the granularity of RxNorm (see Supplementary File/List11-Analysis4 bis). The four analyses were repeated, now taking into account the newly created characteristic \"systemic/local\", resulting in a slightly higher granularity and a slightly lower level of aggregation, but more clinically relevant collections of PDFs (see Table 1 and Supplementary file/list7-Analysis-1 to List10-Analysis-4). Next, the basic new file was ordered by identical combinations of values of the four characteristics (the result of Analysis 3), rearranged by intended site, putting the combinations without transformation first, followed by the combinations with transformation (see Supplementary File/List12-Reorg). For each collection of PDFs with identical combinations, a qualitative evaluation was conducted with regard to the need to further split the collection to create homogeneous classes, with regard to systemic effect or to concatenate collections with another similar collection or collections (to create relevant new classes). These decisions were made based on a lack of clinical relevance to keep them apart, or on the need to separate dose forms with a different expression of strength or effect on the body (systemic/local). Further, the unique combinations with only one occurrence were examined for possible concatenation. Finally, labels were discussed for the retained similar collections of PDFs. This resulted in a simple three-level ontology (merely a taxonomy), with a first level of 22 slightly amended values of \"intended site\", and a second level of 69 newly created terms for the collections with similar combinations, and the third level, the 428 granular EDQM PDFs (see Table 2 for the first two levels of the ontology and Supplementary File/List13--Ontology for the three levels).