DIPPER: Description and Formalisation of an Information-State Update Dialogue System Architecture Johan Bos author Ewan Klein author Oliver Lemon author Tetsushi Oka author 2003 text Proceedings of the Fourth SIGdial Workshop of Discourse and Dialogue conference publication bos-etal-2003-dipper https://aclanthology.org/W03-2123/ 2003 115 124