A relational algebra for user-defined periodicity

Calendars and periodicity play a fundamental role in many applications. Recently, some commercial databases started to support user-defined periodicity in the queries, providing high level languages to this purpose (e.g., TimeSeries in Oracle 8). On the other hand, existing relational data models do not support user-defined periodicity in the data, with few exceptions. We sketch a high level "symbolic" language for representing periodicity in a "human oriented" way, and propose a temporal relational model which supports user-defined "symbolic" periodicity in the validity time of tuples. We also define the temporal counterpart of the standard operators of the relational algebra, and introduce new temporal operators and functions. Finally, we sketch a symbolic implementation of the algebraic operators.