A method and system provide the ability to determine matching subjects for features provided in a stimulus. Subject information is pre-processed by receiving input (a feature type definition and a subject set) and building BitSets across all subjects in the subject set. The stimulus is received and includes stimulus features. For each feature type in the stimulus features, all feature type BitSets from the subject set that match are assembled. An evaluation BitSet is built by combining the assembled feature type BitSets. Matching subjects that match the stimulus are determined based on the evaluation BitSet.