A historical query language, hquel, is designed as a minimal extension to quel, which is the query language of the database management system ingres. In the underlying data model, each attribute value is stored along with the time interval over which the value is valid. hquel includes new range declarations, set theoretic expressions, and conditions. Aggregate functions of quel are also extended for historical data. A new clause, “when”, is added to aggregate function definition to make aggregation over the time dimension easier. Semantics of time is embedded within the quel semantics without any major modifications. hquel also manipulates set-valued attributes in N1NF relations.