Consider the following relations for a database that keeps track of business trips of salespersons in a sales office:
SALESPERSON (SSN, Name, Start_Year, Dept_No)
TRIP (SSN, From_City, To_City, Departure_Date, Return_Date, Trip_ID)
EXPENSE (Trip_ID, Account#, Amount)
Specify the foreign keys for this schema, stating any assumptions you make.
The schema of this question has the following two foreign keys:
1. the attribute SSN of relation TRIP that references relation SALESPERSON, and
2. the attribute Trip_ID of relation EXPENSE that references relation TRIP.
In addition, the attributes Dept_No of relation SALESPERSON and Account# of relation
EXPENSE are probably also foreign keys referencing other relations of the database not mentioned in the question. We now give the queries in relational algebra:
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