\draw (doctor) -- (treats); \draw (patient) -- (treats); \draw (date) -- (treats);
\node at ($(doctor)!0.5!(treats)$) [left] M; \node at ($(patient)!0.5!(treats)$) [left] M; \node at ($(date)!0.5!(treats)$) [right] M; \endtikzpicture \captionTernary Relationship: TREATS \endfigure \noindent The relationship has cardinality M:M:M. In tables, the composite key is (doctor\_id, patient\_id, date).
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