
148 ◾ Secure Data Provenance and Inference Control
A vertex contraction of the LHS of Figure 10.3 would therefore replace Physician1_1
and Surgeon1_1 with a triangle that denotes a merge of these two nodes.
is vertex contraction could show for example how a third party is prevented
from knowing the identities of agents (i.e., both a patient’s primary physician and
surgeon) who controlled the processes (i.e., a heart surgery and a logging of results
of a surgery into a patient’s record).
Path contraction. is occurs on a set of edges in a path that contract to form a
single edge between the end points of the path. Edges incident to vertices a