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Antonis Kakas and Rob Miller
Reasoning about Actions, Narratives and Ramification

Rob Miller:

Hector Geffner (ENAI 10.11) wrote:

Now, Rob is right; dynamic systems come in different varieties; e.g., discrete time, discrete value space discrete time, continuous value space continuous time, continuous value space .... Rules like the one above (with first order extensions, etc) are good for specifying systems of Type 1 only. Yet it's not difficult to see how systems of Type 2 could be specified as well. Actually there are *other* type of mathematical models for the type of problems that Rob has in mind as the "Semi-Markov Decision Processes" (probabilistic continuous processes - like queuing systems - that are controlled at discrete time intervals).

That's right. But I think that an important wider problem that we have to tackle within "reasoning about action and change" is how to synthesise or combine very different approaches to modelling dynamic systems within a single "commonsense" framework. For example, I'd like to see more research along the lines of Erik Sandewall's 1989 work on combining reasoning about actions with modelling using the differential calculus. It's true that there has been a small amount of subsequent work on this theme since then (see e.g. http://www.dcs.qmw.ac.uk/~rsm/project.html#Other for a bibliography). But not much compared with, say, work on extending state-transition based approaches to deal with ramifications in evermore sophisticated ways. Why is this so? Why don't we put much effort into addressing challenges such as Kuipers' - on combining the Situation Calculus with Q.R. (see Kuipers' book, p. 201)? If we did more of this type of work, we'd stand more chance of being able to (in Hector's words) "package the theory for the outside world".

Rob