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The dotted
box in the top left corner shows the set of objects that are
PERSONS.
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1
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Primary Key column
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2, 3 ...
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Alternative (secondary) key column
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FK
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Foreign Key column
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(V)
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Virtual column: field value is derived from a different base
table (also referred to as 'joined column').
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(X)
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Exclusivity rule: each supertype can be ONLY ONE of its
subtypes.
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(D)
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Deduction: value (for RESERVATION.GROUP_DISCOUNT) is deduced
from (number of related records in the PARTICIPANT table and data
in the DISCOUNT table).
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