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 December 5, 2024. https://stipendii.uni-sofia.bg/index.php/fmi/article/view/459.