Arcs

• ·         A curved line used to represent an exclusive relationship in an entity-relationship diagram - Arc
• ·         A logical operator that returns a true value if one, but not both, of its operands is true. - Exclusive OR
• ·         A relationship between one entity and two (or more) other entities when only one of the relationships can exist at a time. - Exclusive OR Relationship/ mutually exclusive relationship
• ·         A restriction that applies to data, which is often dictated by the business rules. - constraint

1. A show ticket is purchased from an agent, the box office, or the Internet. A ticket has a description, an event, a date and a price. An agent has a name and a phone number. The box office has an address and a phone number. The Internet has a URL address.

Draw the entities and represent the mutually exclusive relationship.

Assume that all type of sellers it for same price.  One Ticket Instance must be booked by one and only of (one Agent Instance, one box office instance or one website instance)

2. Draw the MENU entity as a supertype of the PROMOTIONAL, REGULAR, and OTHER entities. The UID of MENU is code. MENU is related to FOOD ITEM through this relationship: each MENU may contain one or more FOOD ITEMs, and each FOOD ITEM must be listed on one and only one MENU. The UID of FOOD ITEM is a barred UID using its attribute “number”. Add appropriate attributes to the other entities and be ready to defend your choices.