1. A method of generating an invocation sequence of update functions that update values associated with questions in a questionnaire form used to obtain information to produce a customized document from a template document, the invocation sequence specifying an order in which the update functions are invoked, the method comprising the steps of: supplying the update functions to a synthesiser; identifying, using the synthesizer, trigger questions from the questions of the questionnaire form that trigger invocation of at least one of the supplied update functions; generating an activation network based on the identified update functions at the synthesiser; and determining the invocation sequence of the identified update functions for each trigger question by using the activation network.