A temporal relational algebra based on multiple time-lines

A clocked temporal relational algebra, called ℜ, which supports temporal relations based on multiple time-lines is proposed. Temporal relations are defined over clocks which are subsequences of an assumed global time-line. The algebra is a consistent extension of the relational algebra, and it includes a number of temporal operators to combine data based on different time-lines. The meaning of an operation of ℜ depends on the clocks of the relations involved in the operation as well as the relations. We outline a formal interpretation of expressions of ℜ, and sketch a naive expression evaluation method