Database Schema SUPPLIER ( SName , ItemName , Price ) - A supplier SName sells an item ItemName at Price . CUSTOMER ( CName , Address ) - A customer CName lives at Address . ORDER ( CName , SName , ItemName , Qty ) - A customer CName has ordered Qty of item ItemName from supplier SName . ITEM ( ItemName , Description ) - Information about items. Additional Constraint Every item is supplied by some supplier. Components of the EER Diagram Entities : SUPPLIER , CUSTOMER , ITEM Relationships : Between SUPPLIER and ITEM (supplies), between CUSTOMER and ORDER (places), and between ORDER and ITEM (involves) Keys SName for SUPPLIER CName for CUSTOMER ItemName for ITEM Composite key ( CName , SName , ItemName ) for ORDER Structural Constraints A supplier can supply many items, but each item must be supplied by at least one supplier (1:N relationship between SUPPLIER and ITEM ). A customer can place many orders, but each order is placed by exactly one customer (1:N relationship between CUSTOMER and ORDER ). An order can involve multiple items, and an item can be part of multiple orders (M:N relationship between ORDER and ITEM ). Roles and Notation The roles can be explicitly stated in the relationships, such as supplies for the relationship between SUPPLIER and ITEM , and places for the relationship between CUSTOMER and ORDER . Use traditional ER notation with single lines indicating mandatory participation and double lines for optional participation. Min-max notation can also be used to specify the constraints (like 1:N, M:N). Additional Assumptions Assume that each order specifies only one type of item but can specify multiple quantities. Assume ItemName in ITEM is unique across all suppliers. Drafting the EER Diagram Create entities for SUPPLIER , CUSTOMER , ITEM , and ORDER . Define supplies relationship between SUPPLIER and ITEM . Define places relationship between CUSTOMER and ORDER . Define involves relationship between ORDER and ITEM . Include attributes for each entity and specify keys. Show participation and cardinality using appropriate ER notations.

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