\sectionExercise 5: Weak Entity Example (Order-Item) \textbfScenario: \\ An e-commerce system has orders and line items. \beginitemize \item \textbfOrder: order\_number (PK), order\_date, customer\_name. \item \textbfLine Item: item\_number (only unique per order), product\_name, quantity, price. \item A line item cannot exist without an order. The combination (order\_number, item\_number) uniquely identifies a line item. \enditemize
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\section*Appendix: Quick ERD Notation Reference \begintcolorbox \begintabular \hline \textbfSymbol & \textbfMeaning \\ \hline Rectangle & Entity \\ Oval & Attribute (sometimes omitted, listed inside entity) \\ Diamond & Relationship \\ Underline & Primary Key \\ Double Rectangle & Weak Entity \\ Double Diamond & Identifying Relationship \\ 1 at line end & One cardinality \\ M or * at line end & Many cardinality \\ Circle (O) & Optional participation \\ \hline \endtabular \endtcolorbox entity-relationship diagram exercises and answers pdf
% Lines \draw (student) -- (enroll) node[midway, left] M; \draw (course) -- (enroll) node[midway, right] M; \item A line item cannot exist without an order
\vspace2cm \noindent\rule\textwidth0.5pt \textbfAnswer: \beginfigure[H] \centering \begintikzpicture[node distance=2.5cm] \node[rectangle, draw] (member) MEMBER \\ \tiny member\_ID (PK) \\ name \\ phone; \node[rectangle, draw, right=3cm of member] (book) BOOK \\ \tiny ISBN (PK) \\ title \\ author \\ year; \node[diamond, draw, aspect=2, below=1.5cm of $(member.south)!0.5!(book.south)$] (borrows) BORROWS; \node[below=0.2cm of borrows] \tiny borrow\_date, return\_date; \draw (course) -- (enroll) node[midway