Table 4.

Comparison of cross-referencing performance on the example data set.

Databases	CAS Registry number	KEGG ID	InChI	Any identifier
Only reference libraries	124	58	0	124
PlantCyc	125	82	74	125
GMD	199	146	0	202
ChEBI	124	58	54	124
KEGG	131	111	0	131
PRIMe chemical standards	168	158	166	168
All (MetMask)	235	222	231	238

Comparison of cross-referencing performance for the 251 identifiers and synonyms found in the example data set. Local reference libraries were combined with the sources listed in column Databases via MetMask and used to convert local identifiers to CAS, KEGG and InChI identifiers. The table lists the number of successfully converted identifiers. Conversion to "Any identifier" indicates the number of local identifiers that could be converted to any other type of identifier (e.g., SMILES, synonym, IUPAC name, etc.). Using all resources together, as performed in the MetMask approach, we obtain a better identifier conversion performance.