1. A computer-implemented method, comprising: receiving availability requests from requestors of availability information; prioritizing the availability requests, wherein the prioritizing includes prioritizing the availability requests based at least in part on time remaining prior to events associated with the requested availability information; processing the availability requests according to the priorities; selecting one or more availability information sources to be queried for each of the availability requests based at least in part on policies associated with the requestors; querying the selected availability information sources; and providing results from the querying to the requestors.