Patent US 6,466,930

A data processing method evaluates expressions, including temporally-scoped operands, to produce temporally-scoped results. Each of the temporally-scoped operands and results includes a sequence of one or more value instances, each value instance including a data item, a start time, and an end time, the start time and end time defining a time span in which the data item is valid. An expression involving a binary operator is evaluated by scanning each of the operands of the binary operator and generating a value instance in the result, in respect of each time span in which each operand has a constant value.