 Through the study of data sourcing and processing in epidemiology, Stefano Canali has instead highlighted the difficulties of deriving mechanistic claims from big data analysis, particularly where data are varied and embodying incompatible perspectives and methodological approaches (Canali 2016, 2019). Relatedly, the semantic and logistical challenges of organising big data give reason to doubt the reliability of causal claims extracted from such data. In terms of logistics, having a lot of data is not the same as having all of them, and cultivating illusions of comprehensiveness is a risky and potentially misleading strategy, particularly given the challenges encountered in developing and applying curatorial standards for data other than the high-throughput results of “omics” approaches (see also the next section). The constant worry about the partiality and reliability of data is reflected in the care put by database curators in enabling database users to assess such properties; and in the importance given by researchers themselves, particularly in the biological and environmental sciences, to evaluating the quality of data found on the internet (Leonelli 2014, Fleming et al. 2017). In terms of semantics, we are back to the role of data classifications as theoretical scaffolding for big data analysis that we discussed in the previous section. Taxonomic efforts to order and visualise data inform causal reasoning extracted from such data (Sterner &amp; Franz 2017), and can themselves constitute a bottom-up method—grounded in comparative reasoning—for assigning meaning to data models, particularly in situation where a full-blown theory or explanation for the phenomenon under investigation is not available (Sterner 2014).