5. The system of claim 1 , wherein receiving program input specifying an aggregation function agg having an input type and an output type comprises: receiving program input comprising language elements specifying, explicitly or implicitly, the aggregation construct for the aggregation function agg, the aggregation function agg having multiple input types, and a relation t that is a relation from the range of s to the multiple input types of the aggregation function agg.
5. The system of claim 1 , wherein receiving program input specifying an aggregation function agg having an input type and an output type comprises: receiving program input comprising language elements specifying, explicitly or implicitly, the aggregation construct for the aggregation function agg, the aggregation function agg having multiple input types, and a relation t that is a relation from the range of s to the multiple input types of the aggregation function agg. 6. The system of claim 5 , wherein the aggregation function agg is a sum, average, count, min, max, product, or concatenation function.