It may be desired to query a large record of events to retrieve certain segments of the data that provide information of interest. However, the data might not be structured such that it is conducive to generate/execute queries that inquire about net changes of events over time. Query language may also be interpreted differently by different analysts. In some embodiments data related to events is assembled into a data structure having a format logically equivalent to a double entry transition table. Each event may have two entries in the table: a first entry representing the event as a transition from a previous state to a current state, and a second entry representing the reverse transition of the first entry. In some embodiments, a query executor tool may be provided as a graphical user interface for entering information of interest to be queried.