Modeling and querying temporal data

The paper discusses modelling temporal variation of data in the context of the relational data model. This is done by employing time-stamps, which leads to two possible approaches: adding time-stamps to tuples and using first normal-form (1NF) relations, and adding time-stamps to attributes and using non-first normal form (NINF) relations. Modelling temporal data according to each approach with their respective data-manipulation operations are covered. This is followed by a discussion that includes the advantages and expressive power of each approach, the classification of temporal databases, and the handling of retroactive and postactive changes.