The statistics in the CoNLL 2004 and 2005 shared tasks (Shen and Lapata, 2007) shows that the semantic roles of ARG0/agent and ARG1/patient account for 85% of all arguments and most likely act as the centers of the local focus structure in discourse due to the close relationship between subject/object and agent/patient.
given the centering theory as described above, we can draw the following conclusions: 1) The centering theory is discourse-related and centers are discourse constructs.