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Figure 1: (a) A 2-class heterogeneous network (2-HN) modeling the complex system of a TCM formula and its molecular targets. A 2-HN can be simply divided into three subnetworks in chemical, pharmacological, and genomic space in terms of the type of links. (b) A pharmacological unit identified from the 2-HN in (a). A pharmacological unit includes a set of structure-similar herbal compounds and a group of function-similar target genes, indicating that the herbal compounds modulate the activities of gene products.