4.5.
CREATE TABLE people (
STRING ssn,
STRING name,
STRING address,
STRING phone_number,

PRIMARY KEY(ssn)
);

CREATE TABLE clients (
STRING ssn;
STRING work_phone_number

PRIMARY KEY(ssn),
FOREIGN KEY (ssn) REFERENCES people
);

CREATE TABLE brokers (
STRING ssn;
STRING phone_extension_number,

PRIMARY KEY(ssn),
FOREIGN KEY (ssn) REFERENCES people
);

CREATE TABLE accounts (
INT number,
DATE date_opened,
??? status,
STRING handled_by_broker_ssn,

PRIMARY KEY(number),
FOREIGN KEY(handled_by_broker_ssn) REFERENCES brokers(ssn)
);

CREATE TABLE offices (
STRING phone_number,
STRING address,

PRIMARY KEY(phone_number),
UNIQUE(address)
);

CREATE TABLE has_account (
STRING client_ssn,
STRING account_number,
STRING office_phone_number,

PRIMARY_KEY(client_ssn, office_phone_number)

FOREIGN KEY (client_ssn) REFERENCES clients(ssn),
FOREIGN KEY (account_number) REFERENCES accounts(number),
FOREIGN KEY (office_phone_number) REFERENCES offices(phone_number)
);

CREATE TABLE works_in (
STRING office_phone_number,
STRING broker_ssn,
DATE since,

PRIMARY KEY(office_phone_number),

FOREIGN KEY (office_phone_number) REFERENCES offices(phone_number),
FOREIGN KEY(broker_ssn) REFERENCES brokers(ssn)
);

CREATE TABLE managed_by (
STRING broker_ssn,
STRING office_phone_number,
DATE since,

PRIMARY KEY (broker_ssn),
UNIQUE (office_phone_number),

FOREIGN KEY (office_phone_number) REFERENCES offices(phone_number),
FOREIGN KEY(broker_ssn) REFERENCES brokers(ssn)
);


4.6. Starting out with an Office, going through IsHandledBy to a Broker, then back over through WorksIn, to an Office, you may end up with a different Office than you started with. This is because there is no specification for how IsHandledBy and WorksIn relate to each other.