We describe our experience with engineering the dialog state tracker for the first Dialog State Tracking Challenge (DSTC). Dialog trackers are one of the essential components of dialog systems which are used to infer the true user goal from the speech processing results. We explain the main parts of our tracker: the observation model, the belief refinement model, and the belief transformation model. We also report experimental results on a number of approaches to the models, and compare the overall performance of our tracker to other submitted trackers. An extended version of this paper is available as a technical report (Kim et al., 2013).