References

KKR95

P.C. Kanellakis, G.M. Kuper, and P.Z. Revesz. Constraint Query Languages. JCSS, 51(1): 26--52, 1995.

GK96

D.Q.Goldin, P.C. Kanellakis. Constraint Query Algebras. J. Constraints, 1(1): 1-41, 1996.