Cotelea V., Ceban Ia.
Four types of cycle on hypergraph are examined: $\beta$-cycle, week $\beta$-cycle, Graham cycle, independent cycle. It is shown that between these types of cycle exists the following relations: $\beta$-cycle $\Rightarrow$ week $\beta$-cycle $\Rightarrow$ Graham cycle $\Rightarrow$ independent cycle. Several necessary and sufficient conditions for database schemes to be $\beta$-acyclic are exposed.
Institutul de Matematică Academia de Ştiinţe a Moldovei
str. Academiei 5, MD-2028 Chişinău, Moldova