  We present an experimental study of large-scale RDF federations on top of the
Bio2RDF data sources, involving 29 data sets with more than four billion RDF
triples deployed in a local federation. Our federation is driven by FedX, a
highly optimized federation mediator for Linked Data. We discuss design
decisions, technical aspects, and experiences made in setting up and optimizing
the Bio2RDF federation, and present an exhaustive experimental evaluation of
the federation scenario. In addition to a controlled setting with local
federation members, we study implications arising in a hybrid setting, where
local federation members interact with remote federation members exhibiting
higher network latency. The outcome demonstrates the feasibility of federated
semantic data management in general and indicates remaining bottlenecks and
research opportunities that shall serve as a guideline for future work in the
area of federated semantic data processing.
