# From domain calculus to relational algebra

by Sena Aydin   Last Updated June 29, 2018 12:06 PM

I have an assigned task at the uni and I have 3 relations as following:

Customer (Name, City, Account)

Offer (Product_Description, Supplier, Price)

Order (Name, Product_Description, Quantity, Supplier)

F = {Name, City| ∃ Account, Product_Description, Supplier, Price, Quantity (customer(Name, City, Account)

∧offer(Product_Description, Supplier, Price)

∧ order(Name, Product_Description, Quantity, Supplier)

∧ Price≥ 100 ∧ Supplier= ’Meier’)}

I have been asked to express this domain calculus as a sentence and convert it to relational algebra:

The expression is: List the name and cities of the customers who ordered a product that has a value greater than or equal to 100 and product supplier is Meier. . (I didn’t use “customers who ordered greater than or equal to 100” because it’s possible that the customer ordered, for example, 2 products (quantity is 2) which has a value of 50 euros.)

Relational Algebra:

I am not sure if my relational expression is accurate. There are many ways to express it but I tried to find the best efficient way for execution plan. (Equivalence of expressions)

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