Hi i am new,

I have a problem in understanding the query decomposition in D-DB. Can anyone help me to understand the first question of the exercise 25.21 of Elmasri-Navath 4th edition?


Consider the following relations:

BOOKS (Book#, Primary_author, Topic, Total_stock, $price)
BOOKSTORE (Store#, City, State, Zip, Inventory_value)
STOCK (Store#, Book#, Qty)

Consider a distributed database for a bookstore chain called National Books with 3 sites called EAST, MIDDLE, and WEST.
Consider that BOOKS are fragmented by $price amounts into:

B1:BOOK1:up to $20.
B2:BOOK2:from 20.01 to $50.
B3:BOOK3:from 50.01 to $100.
B4:BOOK4100.01 and above.

Similarly, BOOKSTORES are divided by Zipcodes into:

S1:EAST:Zipcodes up to 35000.
S2:MIDDLE:Zipcodes 35001 to 70000.
S3:WEST:Zipcodes 70001 to 99999.

Assume that STOCK is a derived fragment based on BOOKSTORE only.

a. Consider the query:
SELECT Book#, Total_stock
FROM Books
WHERE $price > 15 and $price < 55;

Assume that fragments of BOOKSTORE are non-replicated and assigned based on region. Assume further that BOOKS are allocated as:

EAST:B1,B4.
MIDDLE:B1,B2.
WEST:B1,B2,B3,B4.

Assuming the query was submitted in EAST, what remote subqueries does it generate? (write in SQL).

Is this a conceptual understanding problem ? Or is it an exercise a teacher asked you to perform ? In the second case, not sure the answer will arrive before the deadline...