  We propose a novel structure, the data-sharing graph, for characterizing
sharing patterns in large-scale data distribution systems. We analyze this
structure in two such systems and uncover small-world patterns for data-sharing
relationships. Using the data-sharing graph for system characterization has
potential both for basic science, because we can identify new structures
emerging in real, dynamic networks; and for system design, because we can
exploit these structures when designing data location and delivery mechanisms.
We conjecture that similar patterns arise in other large-scale systems and that
these patterns can be exploited for mechanism design.
