$CLIP^{++}$: an object-oriented extension of a relational DBMS. Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 85, p. 107–119, 1993. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/459. Acesso em: 14 dec. 2025.