A witness testifies under oath at a hearing. A witness may be called to give evidence at a hearing on behalf of all appellants on an appeal case. If the witness is not voluntary, a summons is sent requiring that the witness attend the hearing, otherwise a hearing schedule correspondence is sent to the witness. Examples of witnesses include doctors, public health nurses or other individuals who know about the needs of the appellant(s). A witness can be a registered person or an unregistered participant who is subsequently registered as a representative on the system for the purpose of the appeal.