In this section we discuss the relationship between PDDL+ and several other related formalisms in the literature. In addition, we consider the extent to which PDDL+ addresses the inadequacies of PDDL2.1 in terms of expressive power and convenience. Our paper on PDDL2.1 was published in the Journal of Artificial Intelligence Research Special Issue on the 3rd IPC [Fox LongFox Long2003]. The editors of this special issue invited five influential members of the planning community to contribute short commentaries on the language, indicating their support for, and objections to, the choices we made in the modelling of time and time-dependent change. These were Fahiem Bacchus, Mark Boddy, Hector Geffner, Drew McDermott and David Smith. We now discuss the parts of their commentaries that are relevant to the modelling of durative behaviour and continuous change and explain how we believe PDDL+ addresses the issues raised. It is interesting to note that many of the objections raised by these commentaries are addressed by the start-process-stop model of PDDL+. We begin by considering these commentaries and then go on to discuss related formalisms.