Give an example of a program at site A that requires the join of two tables, one at site B and one at site C. State the assumptions needed to justify the result that, as far as communication costs are concerned, the best implementation is to ship the table at site B to site C, do the join there, and then send the result to site A.
What will be an ideal response?
The three alternatives are
1. Send the table at site B to site C, do the join there, and then send the result to site A. The total communication cost is the number of bytes in the table in site B, plus the number of bytes in the join. (bytes C + bytes J)
2. Send the table at site C to site B, do the join there, and then send the result to site A. The total communication cost is the number of bytes in the table in site C, plus the number of bytes in the join. (bytes C + bytes J)
3. Send both tables to site A and do the join there. The total communication cost is the number of bytes in the table in site B, plus the number of bytes in the table in site C. (bytes B + bytes C)
The ?rst alternative is better than the second if
bytes B + bytes J ? bytes B + bytes C
Simplifying the math
bytes B ? bytes C
and
bytes J ? bytes C
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What will be an ideal response?
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FIGURE 1-1
In Figure 1-1 above, which number subsystem is used for long-term storage of data and programs?
A. 1 B. 2 C. 3 D. 4
________ uses a dedicated connection between two points with the connection remaining active for the duration of the transmission.
A. Packet switching B. An open circuit C. Circuit switching D. A closed circuit