The second type, restricted reference databases, is built from taxonomically relevant proteomes, informed by prior knowledge of the sample's composition. This approach is particularly useful for defined microbial communities, such as the SIHUMIx mock community used in the CAMPI study , or when taxonomic data from methods like 16S rRNA gene sequencing is available. However, it is limited by the availability of comprehensive reference proteomes in public repositories, which are often sparse or incomplete for many bacterial species.