In our experiments with artificial domains, we found PLTLSTR and FLTL preferable to state-based PLTL approaches in most cases. If one insists on using the latter, we strongly recommend preprocessing. FLTL is the technique of choice when the reward requires tracking a long sequence of events or when the desired behaviour is composed of many elements with identical rewards. For response formulae, we advise the use of PLTLSTR if the probability of reaching the goal is low or achieving the goal is very costly, and conversely, we advise the use of FLTL if the probability of reaching the triggering condition is low or if reaching it is very costly. In all cases, attention should be paid to the syntax of the reward formulae and in particular to minimising its length. Indeed, as could be expected, we found the syntax of the formulae and the type of non-Markovian reward they encode to be a predominant factor in determining the difficulty of the problem, much more so than the features of the Markovian dynamics of the domain.

Sylvie Thiebaux 2006-01-20