“…This evolution takes place both at tuple level and schema level. Generally, database systems support the notion of non-temporal evolution of tuples and schema to accommodate changes in the state and structure of an object using the concept of "current view" only (Hurson, 1993;Ling, 1992;Pissinou, 1993;Shoshani, 1984). In these databases, only existing data values are kept using the available schema definitions, and therefore, direct access to past information is not available.…”