Functional interactions of physical entities are also compared with each other. Here, we distinguish between primary and secondary interaction participants. Primary participants are substrates and products in case of biochemical reactions, interactors in case of physical interactions and target genes in case of gene regulation. All other participants, e.g. enzymes and interaction modifiers, are secondary participants. If the primary participants of two or more interactions match, these interactions are considered similar. Two similar interactions may have different stoichiometry, modification and/or localization of the participants. To allow for flexibility, similar interactions are marked as such in the database, but the decision whether they should be considered identical despite mismatching details is left to the user and depends on his specific problem. Moreover, ConsensusPathDB does not provide any additional quality control filters. All interactions provided by the different database sources are treated in the same way. The results of our mapping method applied on the data from the source databases mentioned above are summarized in Table 1. Table 1.Database content and pairwise database overlaps in terms of matching physical entities and similar
