Systems and techniques for indexing and/or querying a database are described herein. Discrete sections and/or segments from documents may be determined by a concept indexing system. The segments may be indexed by concept and/or higher-level category of interest to a user. A user may query the segments by one or more concepts. The segments may be analyzed to rank the segments by statistical accuracy and/or relatedness to one or more particular concepts. The rankings may be used for presentation of search results in a user interface. Furthermore, segments and/or documents may be ranked based on recency decay functions that distinguish between segments that maintain their relevance over time in contrast with temporal segments whose relevance decays quicker over time, for example.