This parameter indicates the biological species to which analyzable PPI data is related; currently human for "Homo sapiens" and ath for "Arabidopsis thaliana" are available.
ID.type
The ID type of the biological genes or proteins, possible values are Entrez gene and Gene symbol when db is Biogrid, or Gene symbol when db is HPRD.
hierarchy
This parameter indicates how many hierarchy are included in the network, currently it can be 0, 1 or 2. Default value is 1.