Chapter 26 Replication and Mobile Databases
Review Questions
26.1 What is data replication?
26.2 Identify the benefits of using replication in a distributed system
26.3 Provide examples of typical applications that use replication.
26.4 Compare and contrast eager with lazy replication.
In the Chapter 25 we examined protocols for updating data that worked on the basis that all
updates are carried out as part of the enclosing transaction. This was necessary because a
distributed transaction accesses different fragments on different sites; in other words, the updates
26.5 What is a replication server?
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26.6 Compare and contract the differ type of data ownership models available in the replication
environment. Provide example for each model.
26.7 Discuss the functionality required of a replication server.
At its basic level, we expect a distributed data replication service to be capable of copying data
from one database to another, synchronously or asynchronously. However, there are many other
functions that need to be provided, including:
Scalability – The service should be able to handle the replication of both small and large
volumes of data.
26.8 Discuss the implementation issues associated with replication.
Some implementation issues associated with the provision of data replication by the replication
server include:
26.9 Discuss how mobile database support the mobile worker.
We are currently witnessing increasing demands on mobile computing to provide the types of
support required by a growing number of mobile workers. Such individuals require to work as if in
26.10 Describe the functionality required of mobile DBMS.
All the major DBMS vendors now offer a mobile DBMS. In fact, this development is partly
responsible for driving the current dramatic growth in sales for the major DBMS vendors. Most
vendors promote their mobile DBMS as being capable of communicating with a range of major
relational DBMSs and in providing database services that require limited computing resources to
match those currently provided by mobile devices. The additional functionality required of mobile
DBMSs includes the ability to:
communicate with the centralized database server through modes such as wireless or Internet
access;
26.11 Discuss the issues associated with mobile DBMSs.
Section 26.4.2 discusses issues with mobile DBMSs. Of particular interest are issues relating to:
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26.12 Discuss the Kangaroo Transaction model.
Exercises
26.13 You are requested to undertake a consultancy on behalf of the Managing Director of DreamHome that
requires an investigation into the data distribution requirements of the organization and to prepare a
report on the potential use of a database replication server. The report should compare the technology
of the centralized DBMS with that of the replication server, and should address the advantages and
disadvantages of implementing database replication within the organization, and any perceived
problem areas. The report should also address the possibility of using a replication server to address
the distribution requirements. Finally, the report should contain a fully justified set of recommendations
proposing an appropriate solution.
26.14 You are requested to undertake a consultancy on behalf of the Managing Director of DreamHome to
investigate how mobile database technology could be used within the organization. The result of the
investigation should be presented as a report that discusses the potential benefits associated with
mobile computing and the issues associated with exploiting mobile database technology for an
organization. The report should also contain a fully justified set of recommendations proposing an
appropriate way forward for DreamHome.