Mobile databases

ADBMS
By:
Dabbal S. Mahara
2018 1

Introduction
 Recent advances in portable and wireless technology have led
to mobile computing, a new dimension in data communication
and processing.
 Portable computing devices coupled with wireless
communications allow clients to access data from virtually
anywhere and at any time.
 The mobile computing platform allows users to establish
communication with other users and to manage their work while
they are mobile.
 This feature is especially useful to geographically dispersed
organizations.
2

Introduction
 What is mobile computing?
• Users with portable computers still have network
connections while they move.
• Mobile Computing is an umbrella term used to
describe technologies that enable people to
access network services anyplace, anytime, and
anywhere.
3

4
Fully connected information space

5
Fully connected information space
 Each node of the information space has some
communication capability.
 Some node can process information.
 Some node can communicate through voice channel.
 Some node can do both
 Can be created and maintained by integrating legacy
database systems, and wired and wireless systems.

Problems in Mobile Computing
 There are a number of hardware and software problems that
must be resolved before the capabilities of mobile computing
can be fully utilized
 Some of the software problems – which may involve data
management, transaction management, and database recovery
– have their origins in distributed database systems
 In mobile computing, the problems are more difficult, mainly
because of:
 The limited and intermittent connectivity afforded by wireless
communications
 The limited life of the power supply(battery)
 The changing topology of the network
 In addition, mobile computing introduces new architectural possibilities
and challenges 6

7
Mobile Objects
• A mobile object is some code that
carries a state
• Lives in a host
• That visits places
• which is let in when trusted
• and barred when untrusted
• and will refuse to go to
untrustworthy places

Mobile Database
 A mobile database is a database that can be connected
to by a mobile computing device over a wireless mobile
network.
 Mobile databases:
• Physically separate from the central database server.
• Resided on mobile devices.
• Capable of communicating with a central database server or
other mobile clients from remote sites.
• Handle local queries without connectivity. 8

Why Mobile Databases?
 Mobile data-driven applications enable us to access any
data from anywhere, anytime.
 Examples:
• Salespersons can update sales records on the move.
• Reporters can update news database anytime.
• Doctors can retrieve patient’s medical history from
anywhere.
 Mobile DBMSs are needed to support these applications
data processing capabilities. 9

Mobile Computing Architecture
 The general architecture of a mobile platform is a distributed
architecture where a number of computers, generally referred to
as Fixed Hosts and Base Stations, are interconnected through a
high speed wired network
 Fixed hosts are general purpose computers that are not typically
equipped to manage mobile units but can be configured to do so
 Base stations function as a gateways to the fixed network for the
Mobile Units; They are equipped with wireless interfaces and
offer network access services of which mobile units are clients
10

Fig: A general architecture of a mobile platform
11

Base Station (BS):
 A network element that interconnects the mobile station
(or Mobile unit (MU)) to the network via the air interface.
 Each cell in the network has a BS associated with it.
 The primary function of a BS is to maintain the air
interface, or medium, for communication to any mobile
unit within its cell.
 Other functions of BS are call processing, signaling,
maintenance, and diagnostics.
12

Mobile Units (MU)
 Also called Mobile Systems (MS) or Mobile Hosts (MH).
 Mobile units are battery-powered portable computers that move freely in a
geographic mobility domain, an area that is restricted by the limited bandwidth
of wireless communication channels.
 It consists of three components: (a) transceiver, (b) antenna, and (c) user
interface.
 The user interface exists only at MU, which consists of a display, a keypad for
entering information, and an audio interface for speaking and hearing voice
conversation. This can be a laptop, a palmtop, or a cell phone, or any other
mobile device.
 A downlink channel is used for sending data from a BS to an MU and an
uplink channel is used for sending data from an MU to its BS.
13

 Wireless Communications:
• The wireless medium on which mobile units and base stations
communicate have bandwidths significantly lower than those of a
wired network
• Some wireless access options allow seamless roaming throughout
a geographical region (e.g., cellular networks), whereas WiFi
networks are localized around a base station;
• Some wireless networks, such as WiFi and Bluetooth, use
unlicensed areas of frequency spectrum, which may cause
interference with other appliances, such as cordless telephones;
• Modern wireless networks can transfer data in units called packets,
that are commonly used in wired networks in order to conserve
bandwidth;
• Wireless applications must consider these characteristics when
choosing a communication option
14

 Client/Network Relationships:
• Mobile units can move freely in a geographic mobility domain, an
area that is circumscribed by wireless network coverage;
• To manage the mobility of units, the entire geographic mobility
domain is divided into one or more smaller domains, called cells,
each of which is supported by at least one base station;
• The mobile discipline requires that the movement of mobile units
be unrestricted throughout the cells of a geographic mobility
domain, while maintaining information access contiguity – i.e.
intercell movement, does not negatively affect the data retrieval
process;
15

 The mobile computing platform can be effectively described under the
client-server paradigm, which means we may sometimes refer to a
mobile unit as a client or sometimes as a user, and the base stations
as servers.
 Each cell is managed by a base station, which contains transmitters
and receivers for responding to the information-processing needs of
clients located in the cell.
 We assume that the average query response time is much shorter than
the time required by the client to physically traverse a cell.
 Clients and servers communicate through wireless channels.
16
Client/Network Relationships:

 Wireless communications for mobile ad-hoc network (MANET) is
different; In a MANNET, co-located mobile units do not need to
communicate via a fixed network, but instead, from their own using cost-
effective technologies such as Bluetooth;
 In a MANNET, mobile units are responsible for routing their own data,
effectively acting as base stations as well as clients; They must be
robust enough to handle changes in the network topology, such as the
arrival or departure of other mobile units
 MANNET 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;
 Resource discovery and data routing by mobile units make computing
even more complicated 19

Characteristics of Mobile Environments
 The characteristics of mobile computing include high
communication latency, intermittent wireless connectivity,
limited battery life, and changing client location
 Latency is caused by the processes unique to the wireless
medium, such as coding data for wireless transfer, and tracking
and filtering wireless signals at the receiver
 Intermittent connectivity can be intentional or unintentional;
unintentional disconnections happen in areas where wireless
signals cannot reach, e.g., elevator shafts or subway tunnels;
Intentional disconnections occur by user intent, e.g., during an
airplane takeoff, or when the mobile device is powered down
20

 Battery life is directly related to battery size, and indirectly related
to the mobile device’s capabilities
 Client locations are expected to change, which alters the network
topology and may cause their data requirements to change
 All these characteristics impact data management, and robust
mobile applications must consider them
 To compensate for high latencies and unreliable connectivity,
clients cache replicas of important, frequently accessed data, and
work offline, if necessary; Besides increasing data availability and
response time, caching can also reduce client power consumption
by eliminating the need to make energy-consuming wireless data
transmission for each data access
21

 The server may not be able to reach a client; A client may be
unreachable because it is dozing – in an energy-conserving state
in which many subsystems are shut down – or because it is out of
range of a base station; In either case, neither client nor server
can reach the other, and modifications must be made to the
architecture in order to compensate for this case;
 Proxies for unreachable components are added to the
architecture; For a client (and symmetrically for a server), the
proxy can cache updates intended for the server; When a
connection becomes available, the proxy automatically forwards
these cached updates to their ultimate destination
22

 Mobile computing poses challenges for servers as well as clients;
 The latency involved in wireless communication makes scalability a
problem; Since latency due to wireless communications increases
the time to service each client request, the server can handle fewer
clients;
 One way servers relieve this problem is by broadcasting data
whenever possible; A server can simply broadcast data periodically;
Broadcast also reduces the load on the server, as clients do not have
to maintain active connections to it
23

 Client mobility also poses many data management challenges;
Servers must keep track of client locations in order to efficiently
route messages to them;
 Client data should be stored in the network location that minimizes
the traffic necessary to access it.;
 The act of moving between cells must be transparent to the client;
 The server must be able to gracefully divert the shipment of data
from one base to another, without the client noticing; Client mobility
also allows new applications that are location-based
24

Types of Data in Mobile Application
 Mobile applications can be categorized in two ways: (1) vertical
applications and (2) horizontal applications.
 In vertical applications users access data within a specific cell, and
access is denied to users outside of that cell. For example, users can
obtain information on the location of doctors or emergency centers
within a cell or parking availability data at an airport cell.
 In horizontal applications, users cooperate on accomplishing a task, and
they can handle data distributed throughout the system. The horizontal
application market is massive; two types of applications most
mentioned are mail-enabled applications and information services to
mobile users.
25

 Data may be classified into three categories:
1. Private data: A single user owns this data and manages it. No other user
may access it.
2. Public data: This data can be used by anyone who can read it. Only one
source updates it. Examples include weather bulletins or stock prices.
3. Shared data: This data is accessed both in read and write modes by
groups of users. Examples include inventory data for products in a
company.
 Public data is primarily managed by vertical applications, while shared
data is used by horizontal applications, possibly with some replication.
Copies of shared data may be stored both in base and mobile stations.
26Types of Data in Mobile Application

Data Management Issues
 From a data management standpoint, mobile computing may be
considered a variation of distributed computing
 Mobile databases can be distributed under two possible scenarios:
1. The entire database is distributed mainly among the wired
components, possibly with full or partial replication; A base station or
fixed host manages its own database with a DBMS-like functionality,
with additional functionality for locating mobile units and additional
query and transaction management features to meet the
requirements of mobile environments
2. The database is distributed among wired and wireless components;
Data management responsibility is shared among base stations or
fixed hosts and mobile units
27

 The distributed data management issues can also be applied to
mobile databases with the following additional considerations and
variations:
• Data distribution and replication – Data is unevenly distributed
among the base stations and mobile units
• Transactions models – Issues of fault tolerance and correctness
of transactions are aggravated
• Query processing – Awareness of where data is located is
important and affects the cost/benefit analysis of query
processing; Query optimization is more complicated because of
mobility and rapid resource changes of mobile units
• Recovery and fault tolerance – The mobile database environment
must deal with site, media, transaction, and communication
failure
28

 Mobile database design – The global name resolution
problem for handling queries is compounded because of
mobility and frequent shutdown
 Location-based service – As clients move, location-dependent
cache information may become stale
 Division of labor – Certain characteristics of the mobile
environment force a change in the division of labor in query
processing
 Security – Mobile data is less secure than that which is left at
the fixed location
29

30
Applications of Mobile Computing
• For Estate Agents
• In courts
• In companies
• Stock Information Collection/Control
• Credit Card Verification
• Taxi/Truck Dispatch
• Electronic Mail/Paging

Challenges
 Disconnection
 Low bandwidth
 High bandwidth variability
 Low power and resources
 Security risks
 Wide variety terminals and devices with different capabilities
 Device attributes
 Fit more functionality into single, smaller device
31

Mobile databases

More Related Content

What's hot

Similar to Mobile databases

More from Dabbal Singh Mahara

Recently uploaded

Mobile databases