Answer and Explanation:
At C:
a.) This SQL sequence represents a remote request.
b.) This SQL sequence represents a remote request.
c.)This SQL sequence represents a distributed request. Note that the distributed request is required when a single request must access two DP sites. The PRODUCT table is composed of two fragments, PRO_A and PROD_B, which are located in sites A and B, respectively.
d.)This SQL sequence represents a distributed request.
Note that UPDATE CUSTOMER and the two INSERT statements only require remote request capabilities. However, the entire transaction must access more than one remote DP site, so we also need distributed transaction capability. The last UPDATE PRODUCT statement accesses two remote sites because the PRODUCT table is divided into two fragments located at two remote DP sites. Therefore, the transaction as a whole requires distributed request capability.
e.)This SQL sequence represents a distributed transaction. Note that, in this transaction, each individual request requires only remote request capabilities. However, the transaction as a whole accesses two remote sites. Therefore, distributed request capability is required.
At A:
f.)This SQL sequence represents a distributed request. Note that the request accesses two DP sites, one local and one remote. Therefore distributed capability is needed.
g.)This SQL sequence represents a remote request, because it accesses only one remote DP site.
h.)This SQL sequence represents a distributed request. In this case, the PRODUCT table is partitioned between two DP sites, A and B. Although the request accesses only one remote DP site, it accesses a table that is partitioned into two fragments: PROD-A and PROD-B. A single request can access a partitioned table only if the DBMS supports distributed requests.
At B:
i.)This SQL sequence represents a remote request.
j.)This SQL sequence represents a distributed request.
k.)This SQL sequence represents a distributed request. (See explanation for part h.)
