Consider the following simplified relational schema for InstantBuy:
OrderDetail(orderNo, itemType) 10,000 records stored in London
Client(clientNo, cCity) 1,000 records stored in Glasgow
ClientOrder(clientNo, orderNo) 100,000 records stored in London
To list the clients in Edinburgh who have ordered items of type 'TV3190', we can use the SQL query:
SELECT C.clientNo
FROM Client C, OrderDetail OD, ClientOrder CO
WHERE C.clientNo = CO.clientNo AND CO.orderNo = OD.orderNo AND
cCity = 'Edinburgh' AND itemType = 'TV3190';
For simplicity, assume that each tuple in each relation is 10 characters long, there are 100 clients who have ordered item 'TV3190', there are 10 clients in Edinburgh and computation time is negligible compared to communication time. The communication system has a data transmission rate of 10,000 characters per second and a 1-second access delay to send a message from one site to another. For the following five possible strategies for this query, calculate the communication times, using the following algorithm:
Communication Time = +(no_of_bits_in_message/transmission_rate_per_bit)
where is the access delay.
State any assumptions necessary to support your calculations.
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