(a) The testimony of witnesses is taken in three (3) modes:
(1) By affidavit;
(2) By deposition;
(3) By oral examination.
(b) An affidavit is a written declaration under oath, made without notice to the adverse party.
(c) A deposition is a written declaration under oath, made upon notice to the adverse party, for the purpose of enabling that party to attend and cross-examine; or upon written interrogatories.
(d) An oral examination is an examination in the presence of the tribunal which is to decide the fact or to act upon it, the testimony being heard by the tribunal from the lips of the witness.