Mobile Information Systems

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Mobile Information Systems

• Jaweed Yazdani
• King Fahd University of Petroleum and Minerals

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Mobile Computing

• Recent advances in wireless technology have led
  to mobile computing
• Mobile computing allows mobile users to establish
  communication with users and systems which is
  especially useful to geographically dispersed
  organizations
• Typical examples - traffic police, taxi
  dispatchers, weather reporting services, news,
  financial market reporting and information
  brokering applications
• Number of hardware as well as software problems
  that must be resolved before the capabilities of
  mobile computing can be fully utilized

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Problems in Mobile Computing

• Designing a reliable and robust architecture
• Data management
• Transaction management
• Database recovery
• In mobile computing, these problems become more
  difficult to solve because
• narrow bandwidth of the wireless communication
  channels
• the relatively short active life of the power
  supply (battery) of mobile units
• The changing locations of required information
  (sometimes in cache, sometimes in the air,
  sometimes at the server).

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Mobile Computing Architecture
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Mobile Architecture Main Components

• Distributed architecture
• Fixed Hosts, Base Stations and Mobile Units
• Interconnected through a high-speed wired network
• Fixed hosts are general purpose computers
• Base stations equipped with wireless interfaces,
  can communicate with mobile units to support data
  access
• Mobile Units and base stations communicate
  through wireless channels having bandwidths
  significantly lower than those of a wired network

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Mobile Clients

• Mobile units are battery-powered portable
  computers that move freely in a geographic
  mobility domain
• Restricted by the limited bandwidth of wireless
  communication channels
• The entire geographic mobility domain is divided
  into smaller domains called cells
• The mobile discipline requires that the movement
  of mobile units be unrestricted within the domain
• Conceptually same as the client-server paradigm,
  mobile unit as a client or sometimes as a user,
  and the base stations as servers

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Mobile Environment Characteristics

• Rapid data changes
• Users often query database servers to remain
  up-to-date
• Examples of this type of data are stock market
  information, weather data, and airline
  information
• The database is updated asynchronously by an
  independent external process
• The average duration of a users stay in the cell
  is referred to as residence latency (RL)
• Both the response time and the active life of the
  mobile power source (battery) are important
• Active Mode vs Doze Mode

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Mobile Applications Types of Data

• Mobile applications categories
• vertical applications users access data within a
  cell only eg. Emergency numbers, parking data
  etc.
• horizontal applications users access data handle
  data throughout a system
• Data is classified into three categories
• Private data A single user owns this data and
  manages it. No other user may access it.
• 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.
• 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

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Data Management Scenarios

• Scenario 1
• Entire database distributed among wired
  components, possibly with full or partial
  replication
• Base station manages own database with a
  DBMS-like functionality
• Additional functionality for locating mobile
  units and
• Query and transaction management features to meet
  requirements of mobile environments

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Data Management Scenarios

• Scenario 2
• Database is distributed among wired and wireless
  components
• Data management responsibility is shared among
  base stations and mobile units

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Data Distribution and Replication

• Data unevenly distributed among base stations and
  mobile units
• Consistency constraints compound the problem of
  cache management
• Caches attempt to provide the most frequently
  accessed and updated data to mobile units

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Transaction Models

• Issues of fault tolerance and correctness of
  transactions are aggravated in the mobile
  environment
• A mobile transaction is executed sequentially
  through several base stations and possibly on
  multiple data sets depending upon the movement of
  the mobile unit
• Traditional ACID properties of transactions may
  need to be modified and new transaction models
  must be defined

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Query Processing

• Awareness of where data is located is important
• Location affects cost/benefit analysis of query
  processing
• Query response needs to be returned to mobile
  units that may be in transit or may cross cell
  boundaries yet must receive complete and correct
  query results.

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Recovery and Fault Tolerance

• The mobile database environment must deal with
  site, media, transaction, and communication
  failures
• Site failure at an MU is frequently due to
  limited battery power
• If an MU has a voluntary shutdown, it should not
  be treated as a failure
• Transaction failures are more frequent during
  handoff when an MU crosses cells.

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Intermittently Synchronized Mobile Databases

• A server or a group of servers manages the
  central database
• Clients carry laptops or palmtops with a resident
  DBMS software to do "local" transaction activity
• Whenever clients connects, they receive updates
  to be installed on their local database
• Primary characteristic of this scenario is that
  clients are mostly disconnected the server is
  not necessarily able to reach the client
• Intermittently Synchronized Database Environment
  (ISDBE), and the corresponding databases as
  Intermittently Synchronized Databases (ISDBs).

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ISDBE Characteristics

• A client connects to server when it wants to
  receive updates from a server or to send its
  updates to a server or to process transactions
  that need nonlocal data.
• This communication may be unicastone-on-one
  communication between the server and the
  clientor multicastone sender or server may
  periodically communicate to a set of receivers or
  update a group of clients
• A server cannot connect to a client at will
• Issues of wireless versus wired client
  connections and power conservation are immaterial

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ISDBE Characteristics (Contd.)

• A client is free to manage its own data and
  transactions while it is disconnected. It can
  also perform its own recovery to some extent.
• A client has multiple ways of connecting to a
  server and, in case of many servers, may choose a
  particular server to connect to based on
  proximity, communication nodes available, etc