The Contact relation scheme attributes are:

• Contact first name, a person's first name.
• Contact last name, a person's last name.
• Contact street, a street address.
• Contact zip code, a zip code designated by the United States Postal Service.
• Contact city, a city name in the United States.
• Contact state, a state abbreviation, external key defined by the United States Postal Service.

The primary key attributes of the Contact relation are first name, last name, and street. These attributes, together, functionally determine the other three attributes in the relation. The zip code attribute, not a part of the primary key, functionally determines the city and state, and is therefore a subkey of the relation.

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