10. The system of claim 8 , wherein generating a vector that characterizes the resource, wherein, for each cluster of the set of candidate clusters, a component of the vector indicates a degree to which the cluster was active in generating the set of words comprises: selecting, for the probabilistic model, one or more states that are likely to generate the set of words; generating, using the one or more selected states and for each cluster in the set of candidate clusters, a respective likelihood that the cluster is active in generating the set of words; and generating, based on the respective likelihoods, a vector that characterizes the resource, wherein the vector includes a respective component for each cluster of the set of candidate clusters, and wherein each component indicates a respective likelihood that the cluster is active in generating the set of words.
11. The system of claim 10 , wherein the respective likelihood that the cluster is active in generating the set of words is based on a ratio of a numerator and a denominator, wherein the numerator is a sum of probabilities for states, in the one or more states, in which the cluster is determined to be active, and wherein the denominator is a sum of probabilities for all states in the one or more states in which the cluster is determined to be active or inactive.