The Web Assistant provides a conversational interface to selected sites on the World Wide Web. Users interact with the assistant by means of a flexible spoken dialogue. This paper describes the goals of the dialogue controller for the assistant and the consequent requirements for a dialogue script representation. The principle objective is to facilitate the efficient authoring of flexible conversational interactions. The assistant operates as a Web 'tour guide', and a key requirement on the dialogue controller is the ability to recognize the appropriate point at which to retake the conversational initiative from the user.