Ii send answer to san jose c i send the query to find

ii. Send answer to San Jose.
c. i. Send the query to find the highest salaried employee to Toronto,
Edmonton, Vancouver, and Montreal.
ii. Compute the queries at those sites.
iii. Return answers to San Jose.
d. i. Send the query to find the lowest salaried employee to New York.
ii. Compute the query at New York.
iii. Send answer to San Jose.
19.11 Compute r ⋉ s for the relations of Figure 19.9.
Answer: The result is as follows.
r ⋉ s = A B C
1 2 3
5 3 2
19.12 Give an example of an application ideally suited for the cloud and another
that would be hard to implement successfully in the cloud. Explain your
answer.
Answer: Any application that is easy to partition, and does not need
strong guarantees of consistency across partitions, is ideally suited to the
cloud. For example, Web-based document storage systems (like Google
docs), and Web based email systems (like Hotmail, Yahoo! mail or GMail),
are ideally suited to the cloud. The cloud is also ideally suited to certain
kinds of data analysis tasks where the data is already on the cloud; for
example, the Google Map-Reduce framework, and Yahoo! Hadoop are
widely used for data analysis of Web logs such as logs of URLs clicked by
users.
Any database application that needs transactional consistency would
be hard to implement successfully in the cloud; examples include bank
records, academic records of students, and many other types of organiza-
tional records.
19.13 Given that the
LDAP
functionality can be implemented on top of a database
system, what is the need for the
LDAP
standard?
Answer: The reasons are:
a. Directory access protocols are simplified protocols that cater to a
limited type of access to data.

Practice Exercises
7
b. Directory systems provide a simple mechanism to name objects in
a hierarchical fashion which can be used in a distributed directory
system to specify what information is stored in each of the directory
servers. The directory system can be set up to automatically forward
queries made at one site to the other site, without user intervention.
19.14 Consider a multidatabase system in which it is guaranteed that at most
one global transaction is active at any time, and every local site ensures
local serializability.
a. Suggest ways in which the multidatabase system can ensure that
there is at most one active global transaction at any time.
b. Show by example that it is possible for a nonserializable global
schedule to result despite the assumptions.
Answer:
a. We can have a special data item at some site on which a lock will
have to be obtained before starting a global transaction. The lock
should be released after the transaction completes. This ensures the
single active global transaction requirement. To reduce dependency
on that particular site being up, we can generalize the solution by
having an election scheme to choose one of the currently up sites to
be the co-ordinator, and requiring that the lock be requested on the
data item which resides on the currently elected co-ordinator.