mobile computing

1. Data Management Issues

2. • Data management technology that can
support easy data access from and to mobile
devices is among the main concerns in mobile
information systems.

3. Mobile database
• Data management technology that enables
the use of databases on the mobile computing
environment.
• The database is more advanced and
challenging than the fixed distributed
databases.

4. Mobile Database Features
• Data are available anywhere independent of the
availability of the fixed network connection.
– mobile users can virtually access any data, anywhere
and anytime, even in the absence of fixed network
connection.
• Databases on both mobile and fixed hosts are
sharable in seamless way.
– In order to support seamless data sharing among
mobile and fixed hosts, we need to employ distributed
computing technologies that should also work
properly even in the disconnection-prone
environments.

5. Mobile Environment Model
• A mobile environment consists of two distinct sets of entities
– mobile hosts and
– fixed hosts.
• Cell
• Mobile hosts are connected by wireless connections to the MSS of
the
• cell where they currently exist.
• A mobile host can move within a cell or between two cells while
retaining its network connection.
• Every host and cell in the system is associated with a unique
identifier.
• A mobile host acts as a data client and a data server at the same
time.
• A fixed host called location server keeps information of locations of
all mobile hosts located within its management coverage.

6. Mobile Environment Model

7. Hierarchical structure of location servers

8. Peer –to-peer Environment model
• MANET applications can be considered as peer-to-
peer, meaning that a mobile unit is simultaneously a
client and a server.
– Transaction processing and data consistency control become
more difficult since there is no central control in this
architecture.
– Resource discovery and data routing by mobile units make
computing in a MANET even more complicated.

9. Mobile Database Characteristics
1. The environment where mobile databases are deployed is a mix of
two different networks, i.e., the fixed network and the wireless
network.
– Fixed network characteristics
• Fixed host location,
• relatively high capacity,
• high reliability, and
• low connection cost.
– Wireless Network characteristics
• dynamic network topology,
• Relatively low capacity,
• low reliability, and
• high connection cost.
• Techniques to avoid compromising database performance due to the
use of wireless network
– Reducing the number of data exchanged via mobile network .
– Reducing the response time of accessing data via mobile network .
– Providing data cache on mobile host.

10. Mobile Database Characteristics
2. Limited resources available to mobile users
– Mobile hosts will likely bring only the fraction of
data they need to access frequently during
mobile.
– consistency requirement on databases (both on
mobile and fixed hosts)
• Techniques to address the problem
– Transaction management for mobile data bases .
– Allocation of mobile database replication on the
fixed network.

11. Mobile Database Characteristics
3. Mobile hosts have low security.
– The worst case, for example, our data on the
mobile host would be completely lost if the
mobile hosts become the subject of theft.

12. Data Management Issues
• Data distribution and replication
• Transactions models
• Query processing
• Caching
• Database Interfaces
• Recovery and fault tolerance
• Location-based service
• Security

13. Data distribution and replication
• Higher data availability and lower cost of
remote access.
• More efficient access to data.
• Higher security.
Generally the available replication technologies
assume the deployment on fixed distributed
environment.

14. Replication issues
• Increasing the number of replicas will result in
the increase of costs for updates and
signaling.
• Mobile hosts can move anywhere and
anytime.

15. Transaction Models
• All transactions must satisfy the ACID
properties
– Atomic
– Consistent
– Isolated
– Durable
• Different concurrent transactions performed
should be serializable
– two-phase locking or timestamping

16. Transaction Models
• Mobile transactions are, in general,
distributed transactions where some actions
are performed in mobile computers and
others in fixed hosts.
• ACID properties are hard to enforce,
especially when the mobile computers are
disconnected. I

17. Query Processing
• Query processing is affected when mobility is
considered.
• It is possible to formulate location dependent
queries. For example: “where is the nearest
gas station?” or “which are the cinemas that
project some film at 8:00pm in this city?”
return different values depending on the
location of the mobile computer.

18. Query Processing
• Query optimization methods try in general to obtain
execution plans which minimize CPU, input/output and
communication costs.
• In centralized environments the cost that affects most is the
input/output.
• In distributed environments, communication cost is the
most important one.
• In a mobile distributed environment, the communication
costs are much more difficult to estimate because the
mobile host may be situated in different locations.
• Dynamic optimization strategies are required in this mobile
distributed context.

19. Caching
• Caching techniques for query processing can
reduce communication costs dramatically.
• Difficult to apply caching techniques in mobile
context because cache contents may change
rapidly or get out-of-date due to mobility.
• Updates to the cache memory may not be sent
due to disconnections of the mobile unit.

20. Database Interfaces
• Design of query interface such as Query By Icons
that
– are convenient to use.
– address the features of screen size.
– address limitations in memory and battery power and
the restricted communication bandwidth.
• How the pen and voice can be used as substitutes
for the mouse and keyboard.
• Implementation of a pen-based graphical
database interface on a computer.

21. Recovery and Fault Tolerance
• Fault tolerance is the ability of a system to perform its
function correctly even in the presence of internal faults.
• Faults can be classified as transient or permanent.
• A transient fault will eventually disappear without any
apparent intervention.
• A permanent fault remains unless it is removed by some
external agency.
• While it may seem that permanent faults are more severe,
from an engineering perspective they are much easier to
diagnose and handle.
• The intermittent transient faults that recur often
unpredictably are the most problematic.

22. Recovery and Fault Tolerance
• The mobile computing environment is
characterized by
– limited resource availability,
– high mobility,
– low bandwidth and
– frequent disconnection.
• These features make the mobile computing
environment more susceptible to transient faults.
• Software faults are the results of problems in
software running on PDAs, e.g., mobile crash.
• Transaction recovery deals with the capability of
ensuring failure atomicity.

23. Location based Services
• Determining the location of mobile users is
one of the most challenging tasks which must
be undertaken in order to enable a location-
based service.
– Non-GPS positioning techniques
• Cell of Origin,
• Time of Arrival,
• Angle of Arrival, and
• and Enhanced Observed Time Difference.

24. Location based Services
• Global Positioning System
– GPS is a relatively mature technology,
– Current receiver hardware is smaller, lighter, cheaper and
uses less power than earlier-generation equipment.
• GPS limitations
– strong attenuation of the satellite signals by buildings.
– GPS does not operate well (or at all) in dense ‘urban
canyon’ areas, or inside buildings. Yet, these are often the
very areas where demand for location based services is the
highest.
– In order to use GPS, the mobile handsets must be modified
to integrate GPS receiver chips.

25. Location based Services
• Assisted GPS
– refers to the GPS positioning technique whereby
there is assistance data provided from a special
GPS server/base station by the mobile telephony
network.
– A-GPS enables GPS positioning even in urban and
indoor areas, where the signal is too weak to be
acquired using standard signal tracking
procedures within the receiver.

26. Location based Services
• Issues
– Diverse mobile mapping standards
– Interoperability
– Market capacity
– User Privacy

27. Thank You