Complex on-demand data retrieval and processing is a characteristic of several applications and com-
bines the notions of querying & search, information filtering & retrieval, data transformation & analysis,
and other data manipulations. Such rich tasks are typically represented by data processing graphs, hav-
ing arbitrary data operators as nodes and their producer-consumer interactions as edges. Optimizing
and executing such graphs on top of distributed architectures is critical for the success of the corre-