GovTrack uses the following RDF vocabularies (ontologies/schemas) in its data exports.

Vote

For describing (majority, 2/3rds, etc.) votes. The vocabulary should be generic enough to describe any vote where agents cast ballots, although more may be needed in the vocabulary to fully describe complex voting types.

Census

For describing census data (for any country/region).

Politico

For describing political organizations, offices, and terms held by politicians in those offices.

USGovt

For describing aspects of the United States Government.

USBill

For describing information specific to bills in the United States Congress.