Azalov, Pavel, and Ventsislav Dimitrov. “$CLIP^{++}$: An Object-Oriented Extension of a Relational DBMS”. Ann. Sofia Univ. Fac. Math. and Inf. 85 (December 12, 1993): 107–119. Accessed November 24, 2024. https://ftl5.uni-sofia.bg./index.php/fmi/article/view/459.