@PhDThesis{ Purver04Thesis,
  author = "Purver, Matthew",
  school = "King's College, University of London",
  title = "The Theory and Use of Clarification Requests in Dialogue",
  year = 2004,
  month = aug,
  url = "http://www.eecs.qmul.ac.uk/~mpurver/papers/purver04thesis.pdf",
}