From Oracle FAQ
An ARC Relationship is an arc symbol used on a data model to indicate that two or more relationships are mutually exclusive (XOR).
- a PERSON entity is either an EMPLOYEE or a CUSTOMER, but not both
- a BANK_ACCOUNT is either for a COMPANY or an INDIVIDUAL, but not both
- a PART can either be a NUT or BOLT or SCREW, but only one of these at a time
ARC relationships are implemented as foreign keys at database level.
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