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It is very important to guarantee that data adheres to certain rules which are determined by application
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For example, assume that a business rule says that no row in the phone_list_table should be allowed unless its person_id value found in the person_id column in the person_info_table (this is to ensure that a person's entity must exist first before the phone number information can be established)
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If an insert or update statement attempts to violate this integrity rule, Oracle must roll back the invalid statement and return an error to the application
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In order to achieve this protection, Oracle provides integrity constraints
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For example, a foreign key (see later) can be defined on the column person_id of phone_list_table which references to the primary key person_id of the person_info_table
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