Mobile Database Systems

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Mobile Database Systems

• Hamzeh Khazaei
• Math Computer Sc. Dep
• Amirkabir University of Technology, (Tehran
  Polytechnic)
• Hamzeh.khazaei_at_aut.ac.ir

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Agenda

• Mobile Database Systems, Intro
• Wireless Network Communication
• Location Handoff Management
• Fundamentals of Database Technology
• Concurrency Control Mechanisms
• Data Processing Mobility
• Transaction Management in MDS
• Mobile Database Recovery
• Wireless Information Broadcast

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Mobile Database Systems

• Outline
• Fully Connected Information Space
• Personal Communication System (PCS)
• Mobile Database Systems (MDS)
• Transaction Management
• Data Caching
• Query Processing
• Data Classification
• Conclusion

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Mobile Database Systems

• Fully connected information space

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Mobile Database Systems

• 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

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Mobile Database Systems

• Fully connected information space

Can be created and maintained by integrating
legacy database systems, and wired and wireless
systems (PCS, Cellular system, and GSM)
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Mobile Database Systems
What is a Mobile Database System (MDS)?

• A system with the following structural and
  functional properties
• Distributed system with mobile connectivity
• Full database system capability
• Complete spatial mobility
• Built on PCS/GSM platform
• Wireless and wired communication capability

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Mobile Database Systems
What is a mobile connectivity?
A mode in which a client or a server can
establish communication with each other whenever
needed. Intermittent connectivity is a special
case of mobile connectivity.
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Mobile Database Systems
What is intermittent connectivity?

• A node in which only the client can establish
  communication whenever needed with the server but
  the server cannot do so.

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Types of Mobility

• Terminal Mobility

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Types of Mobility

• Personal Mobility

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Terminal Mobility

• It allow a Mobile unit (laptop, cell phone, PDA,
  etc) to access desired services from any location
  while in motion or stationary, irrespective of
  who is carrying the unit.
• For example a cell phone can use of network
  service with owner or someone else.
• In terminal mobility, it is the responsibility of
  wireless network to identify communication device.

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Personal Mobility

• A user dose not have to carry any communication
  equipment with him.
• User can use any communication device for
  establishing communication with the other party.
• This facility requires an identification scheme
  to verify the person wishing to communicate.
• Each person has uniquely identified and can use
  any mobile device for communication. (example is
  the internet).

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Wireless Network Communication

• This part deal with architecture of cellular
  communication and identifies hardware software
  component to build mobile database systems.
• All wireless system use electromagnetic waves to
  propagate information from one place to another.
  (radio frequencies).
• Use different frequencies for different purposes.
  

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Cellular Communication

• Geographical area divided to some slots that use
  RF to setup communication in each slots, this
  slots referred to as a cell.
• The entire communication infrastructure is known
  as cellular communication.
• The best coverage pattern is hexagons shapes,
  that no have uncovered space.
• A cell must have a wireless component for
  managing the communication.
• The transceiver is installed in the best place of
  cell.

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Cellular Communication
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Cellular Communication

• In a cellular architecture a number of wireless
  and wired components are required to establish
  the desired point-to-point, point-to-multipoint
  communication.
• One such component is the transceiver, which
  referred as Base Station (BS).
• A BS functions under the supervision of
  telecommunication switch called Mobile Switching
  Center (MSC) and connected to it through wired
  line.

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Cellular Communication
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Structure of a Channel

• In mobile discipline two frequencies are required
  to establish communication one from mobile unit
  (MU) to Base Station (BS) (uplink channel) and
  inverse (downlink channel).

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Downlink and uplink Channel
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PCS GSM

• Personal Communication System
• Evolved in North America
• Support Digital and analogue
• Global System for Mobile Communication
• Evolved in Europe
• Purely Digital

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Personal Communication System (PCS)
Part 1

• Architecture
• Wireless communication
• Bandwidth limitations
• Frequency reuse

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Personal Communication System (PCS)

• A system where wired and wireless networks are
  integrated for establishing communication.

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Personal Communication System (PCS)

• Wireless Components

Base Station (BS) A switch, which serves as
communication link between MU and the entire
network Mobile Units (MU) Also called Mobile
Systems (MS) or Mobile Hosts (MH). A mobile
component, which communicates with BS through a
limited number of wireless channels.
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Personal Communication System (PCS)

• Wireless Components

Home Location Register (HLR) Its a large
database which stores necessary information such
as geographical location of subscriber, call
processing, billing, service subscription,
service restriction, etc. It can be distributed
database. Authentication Center (AC) The AC is
the processor system, witch authenticate
subscribers, AC needs to access user information
for authentication process so its co-located with
HLR, then the AC and HLR store in MSC. The
authentication steps as follows
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Personal Communication System (PCS)

• Wireless Components

1- AC sends a random number to the mobile unit
from where the call originates. 2- Authentication
algorithm stored in SIM (Subscriber Identity
Module) manipulates this random number using a
Subscriber Authentication Key, which is also
stored in SIM. 3- The result of this manipulation
is sent to AC along with an encryption key. 4-
Concurrent with the authentication computation at
the mobile unit, AC performs identical
computation using the random number and
information stored in HLR.
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Personal Communication System (PCS)

• Wireless Components

5- AC compares the result of its own computation
and the result received from the mobile unit. In
the case of successful comparison, it permits the
subscriber to access the network and stores and
sends the encryption key to BS to enable
ciphering to take place. Equipment Identify
Register (EIR) it is a database which stores
information for the identification of mobile
units. It maintains a database of Electronic
Serial Number which is unique to mobile unit
which prevent its theft and malicious use.
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Personal Communication System (PCS)

• Wireless Components

Public Switched Telephone Network (PSTN) This
component refers to the regular wired line
telecommunication network which is commonly
accessed by landline calls. Integrated Service
Digital Network (ISDN) It is a wired line
network which provides enhanced digital services
to subscribers. Short Message Entity (SME) This
is a part of the System Message Service (SMS),
which looks after text messages.
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Personal Communication System (PCS)

• Wireless Components

Message Center (MC) This unit stores and
forwards short messages to mobile destination. If
the destination is unavailable for any reason ,
it stores the message for later dispatch.
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Personal Communication System (PCS)

• Limited channels must be utilized efficiently.
  It is done so by

Frequency reuse The same radio frequency is used
for communication by more than one
cell sessions.
Mobile cells To achieve frequency reuse, the
entire wireless coverage area is divided into
cells.
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Personal Communication System (PCS)

• Mobile cells

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Personal Communication System (PCS)

• Mobile cells
• The entire coverage area is a group of a number
  of cells. The size of cell depends upon the
  power of the base stations.

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Personal Communication System (PCS)

• Frequency reuse

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Personal Communication System (PCS)

• Problems with cellular structure

• How to maintain continuous communication between
  two parties in the presence of mobility?
• Solution Handoff

• How to maintain continuous communication between
  two different service provider?
• Solution Roaming

• How to locate of a mobile unit in the entire
  coverage area?
• Solution Location management

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Personal Communication System (PCS)

• Handoff

A process, which allows users to remain in touch,
even while breaking the connection with one BS
and establishing connection with another BS.
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Personal Communication System (PCS)

• Handoff
• To keep the conversation going, the Handoff
  procedure should be completed while the MS (the
  bus) is in the overlap region.

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Personal Communication System (PCS)

• Handoff issues

• Handoff detection
• Channel assignment
• Radio link transfer

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Personal Communication System (PCS)
Handoff detection strategies

• Mobile-Controlled handoff (MCHO)
• Network-Controlled handoff (NCHO)
• Mobile-Assisted handoff (MAHO)

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Personal Communication System (PCS)

• Mobile-Controlled Handoff (MCHO)

In this strategy, the MS continuously monitors
the radio signal strength and quality of the
surrounding BSs. When predefined criteria are
met, then the MS checks for the best candidate BS
for an available traffic channel and requests the
handoff to occur. MCHO is used in DECT and PACS.
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Personal Communication System (PCS)

• Network-Controlled Handoff (NCHO)

In this strategy, the surrounding BSs, the MSC or
both monitor the radio signal. When the signals
strength and quality deteriorate below a
predefined threshold, the network arranges for a
handoff to another channel. NCHO is used in CT-2
Plus and AMPS.
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Personal Communication System (PCS)

• Mobile-Assisted Handoff (MAHO)

It is a variant of NCHO strategy. In this
strategy, the network directs the MS to measure
the signal from the surrounding BSs and to report
those measurements back to the network. The
network then uses these measurements to determine
where a handoff is required and to which channel.
MACHO is used in GSM and IS-95 CDMA.
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Personal Communication System (PCS)

• Handoff types with reference to the network

• Intra-system handoff or Inter-BS handoff
• The new and the old BSs are connected to the
  same MSC.

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Personal Communication System (PCS)

• Handoff types with reference to the network

• Intersystem handoff or Inter-MSC handoff
• The new and the old BSs are connected to
  different MSCs.

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Personal Communication System (PCS)

• Handoff types with reference to link transfer

• Hard handoff
• The MU connects with only one BS at a time, and
  there is usually some interruption in the
  conversation during the link transition.

• Soft handoff
• The two BSs are briefly simultaneously connected
  to the MU while crossing the cell boundary. As
  soon as the mobile's link with the new BS is
  acceptable, the initial BS disengages from the MU.

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Personal Communication System (PCS)

• Handoff types with reference to link transfer

• Hard handoff
• MU temporarily suspends the voice conversation by
  sending a link suspend message to the old BS.
• MU sends a handoff request message through an
  idle time slot of the new BS to the network.
• The new BS sends a handoff ack message and marks
  the slot busy.
• The MU returns the old assigned channel by
  sending a link resume message to the old BS.

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Personal Communication System (PCS)

• Handoff types with reference to link transfer

• Hard handoff
• MU continues voice communication while the
  network prepares for the handoff.
• Upon receipt of a handoff request message, the
  new BS sends a handoff ack message and
  reconfigures itself to effect the handoff.
• The MSC inserts a bridge into the conversation
  path and bridges the new BS.
• Finally, the network informs the MU to execute
  the handoff via both the new and old BSs by
  sending the handoff execute message.

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Personal Communication System (PCS)

• Handoff types with reference to link transfer

• Hard handoff
• MU releases the old channel by sending an access
  release message to the old BS.
• Once the MU has made the transfer to the new BS,
  it sends the network a handoff complete message
  through the new channel, and resumes the voice
  communication. The network removes the bridge
  from the path and frees up the resources
  associated with the old channel.

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Personal Communication System (PCS)

• Handoff types with reference to link transfer

• Soft handoff
• MU sends a pilot strength measurement message to
  the old BS, indicating the new BS to be added.
• The old BS sends a handoff request message to the
  MSC. If the MSC accepts the handoff request, it
  sends a handoff request message to the new BS.
• The BS sends a null traffic message to the MU to
  prepare the establishment of the communication
  link.

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Personal Communication System (PCS)

• Handoff types with reference to link transfer

• Soft handoff
• The new BS sends a join request message to the
  MSC. The MSC bridges the connection for the two
  BSs, so that the handoff can be processed without
  breaking the connection.
• The new BS sends a handoff ack message to the old
  BS via the MSC. The old BS instructs the MU to
  add a link to the new BS by exchanging the
  handoff command and handoff complete messages.

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Personal Communication System (PCS)

• Handoff types with reference to link transfer

• Soft handoff
• The old BS and the MSC conclude this procedure by
  exchanging the required handoff information. The
  quality of the new link is guaranteed by the
  exchange of the pilot measurement request and the
  pilot strength measurement message pair between
  the MU and the new BS.

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Personal Communication System (PCS)

• Roaming

Roaming is a facility, which allows a subscriber
to enjoy uninterrupted communication from
anywhere in the entire coverage space. A mobile
network coverage space may be managed by a number
of different service providers. They must
cooperate with each other to provide roaming
facility. Roaming can be provided only if some
administrative and technical constraints are met.
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Personal Communication System (PCS)

• Roaming

Administrative constraints

• Billing.
• Subscription agreement.
• Call transfer charges.
• User profile and database sharing.
• Any other policy constraints.

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Personal Communication System (PCS)

• Roaming

Technical constraints

• Bandwidth mismatch. For example, European 900MHz
  band may not be available in other parts of the
  world. This may preclude some mobile equipment
  for roaming.
• Service providers must be able to communicate
  with each other. Needs some standard.
• Mobile station constraints.

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Personal Communication System (PCS)

• Roaming

Technical constraints

• Integration of a new service provider into the
  network. A roaming subscriber must be able to
  detect this new provider.
• Quick MU response to a service providers
  availability.

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Personal Communication System (PCS)

• Location Management

Two-Tier Scheme
HLR Home Location Register A HLR stores user
profile and the geographical location. VLR
Visitor Location Register A VLR stores user
profile and the current location who is a visitor
to a different cell that its home cell.
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Personal Communication System (PCS)

• Location Management

Two-Tier Scheme steps. MU1 wants to talk to MU2.
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Personal Communication System (PCS)

• Location Management

Two-Tier Scheme steps. MU1 wants to talk to MU2.

1. VLR of cell 2 is searched for MU2s profile.
2. If it is not found, then HLR is searched.
3. Once the location of MU2 is found, then the
   information is sent to the base station of cell
   1.
4. Cell 1 establishes the communication.

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Personal Communication System (PCS)

• Location Management

Two-Tier Scheme steps location update

1. MU2 moves from cell 1 to cell 2.
2. MU2s location is changed so new location must be
   recorded.
3. HLR is updated with the new location address.
4. MU2s entry is deleted from the VLR of cell 1 and
   new entry is made in cell 2s VLR.

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Personal Communication System (PCS)

• Location Management

Two-Tier Scheme steps location search
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Location Search

• 1- The Caller dials a number, to find the called
  number (destination), the caller unit sends a
  location query to its base station source base
  station.
• 2- the source base station sends the query to the
  S-LS (source location server) for location
  discovery.
• 3- S-LS first looks up the VLR to find the
  location. If the called number is a visitor to
  the source base station, then the location is
  known and connection is set up.
• 4- If VLR search fails, then the location query
  is sent to HLR.
• 5- HLR finds the location of D-LS (Destination
  Location server)

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Location Search

• 6- The search goes to D-LS
• 7- D-LS finds the address of D-BS (destination
  base station)
• 8- Address of D-BS send to the HLR
• 9- HLR sends the address of D-BS to S-LS (source
  location server)
• 10- The address of D-BS is send to the source
  base station, which sets up the communication
  session.

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Personal Communication System (PCS)

• Location Management

Two-Tier Scheme steps location update
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Location Update

• 1- The mobile unit moves to a new registration
  area which is serviced by a new location server
  (New LS). The mobile unit informs the new base
  station about its arrival.
• 2- The new base station sends the update query to
  new LS.
• 3- The new LS searches the address of the HLR in
  its local database.
• 4- The new location of the mobile unit is sent to
  HLR.
• 5- The old location of the mobile unit is
  replaced by the new location.

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Location Update

• 6- The HLR sends user profile and other
  information to new LS.
• 7-The new LS stores the information it received
  from HLR.
• 8- The new LS informs the new base station that
  location update has been completed.
• 9- the HLR also send a message about this
  location update to the old LS. The old LS deletes
  the old location information of the mobile unit
  stored in its database.
• 10- the old LS sends a confirmation message to
  the HLR.

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• End of part one

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Fundamentals of Database Processing

• The types of DBMS
• Centralized
• There is one node processing (server) and a
  number of intelligent terminals (client)
  connected to the server with wired network
• Distributed
• A number of centralized database systems are
  connected together with a communication network.

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Fundamentals of Database Processing

• The servers can be configured dependent or
  independent.
• Homogeneous or heterogeneous.

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Centralized DBMS
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Distributed DBMS
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Distributed DBMS

• Based on
• Node autonomy
• Data processing
• Distribution mode
• There are two commonly known categories
• Federated database system
• Multidatabase system

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Federated architecture

• Subset of servers are partially autonomous in
  managing their activities
• They are member of federation and willing to
  cooperate and participate with other members
  (servers) under agreed protocols.
• This federation can be homogeneous or
  heterogeneous.
• example is a big company that have many
  department that each have their own server, and
  participate themselves to maintain the consist
  view of the entire company.

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Multidatabase architecture

• All servers have full autonomy
• Its up to server to cooperate or not with any
  other server.

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Database partition and distribution

• In distributed database the database is
  distributed in three ways
• Partitioned
• The entire database is distinctly divided into a
  number of partitions.
• Some important criteria for partitioning
• Support highest database locality
• Minimize the cost of communication
• Minimize the cost of maintaining global
  consistency
• Minimize of recovery

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Partial Replication

• Database is partitioned and a subset of
  partitions is replicated at more than one
  servers.
• Improve database locality and reliability
• The recovery is easier than partitioned
• More time consuming to maintain the global
  consistency

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Full Replication

• The entire database is replicated at all servers
• Maximum locality and minimize data communication
  cost
• Highest reliability and availability
• Maximum cost of maintaining global consistency.
• This schema not used reality, because of higher
  consistency and storage cost.

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Transaction

• Transaction with its property preserve
  consistency of database.
• Constraint can be implement in two ways
• Programmed in the application code
• Included in transaction structure

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Flat Transaction

• Is the simplest type of mechanism which support
  one level operation
• During of their execution, they do not trigger
  other dependent transaction
• It has for essential property
• Atomicity (idempotent property of rollback)
• Consistency
• Isolation
• durability

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Advanced transaction model

• For achieve
• Increase the degree of parallelism in the
  execution of long running transaction
• Redefine consistency to manage statistical
  database transaction
• Handle failure cases in confined way
• Redefine conflict scenario
• Advanced transaction necessary.

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Nested transaction model
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Nested transaction model

• Sub transactions at the leaf are flat transaction
  which actually perform the necessary data
  processing
• Parent does not manipulate any data, but invokes
  sub transactions and controls the flow of
  execution.
• A sub transaction can be commit or rollback
  independent to other sub transactions or the
  parent of the tree.
• A sub transaction has only A,C and I properties,
  because its durability depends only on its
  parent.
• If the parent rolls back, then all its sub
  transaction must be rolled back.

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Nested transaction model

• Open nested transaction model
• The parent does not enforce restriction of the
  execution, rollback, and commitment of its sub
  transactions.
• The parent only invoke sub transaction, and the
  sub transactions executed independently to each
  other and also to the parent.
• Closed nested transaction model

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SAGA transaction model

• SAGA based on compensation transaction and long
  running transaction.
• A transaction can be divided into number of fine
  granularity transaction and chained together,
  then each fine transaction can execute
  independently.
• Its also possible to remedy (compensation) the
  malfunctioning of a single fine transaction
  without effecting others.
• Each sub transaction correspond with the
  compensation transaction.

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SAGA with ACID

• SAGA allows other SAGAs to see the partial
  results of a transaction, as a result SAGA can
  not guarantee complete atomicity
• Consistency and Isolation because of above
  property is not guaranteed
• Durability is preserved because SAGA guarantees
  that the main transaction commits only when al
  its subtransaction are committed.

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Cooperative transaction model
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Cooperative transaction model

• Transaction Group (TG)
• A TG is a parent for a number of cooperative
  transaction, and supervises the activities of
  cooperative members.
• It interact with other TGs with external
  protocols.
• Every TG its own version of a data item which is
  not accessible to other TG.
• All cooperating member can access to this version
• TG does not take part in data processing
• TG plays the role of server for its cooperating
  transaction member.

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Cooperative transaction model

• Cooperative Transaction members
• Operate under internal protocol
• They are like client that issue reads and writes
  on data items which performed by their TG
• TG can either process operation from client
  process, refuse and queue for later processing
• Serialization of member is monitored by TG
• Flexibility in achieving serialization and
  purpose-specific correctness criteria are of the
  contributions of cooperative transaction model.

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Flex Transaction Model

• This model is based on flat transaction
• Allow users to define their data processing
  preferences
• The objective of this model is to minimize ACID
  constraints to allow more flexibility in
  processing concurrent transactions.
• A flex transaction T can be represent as 5-tuple
  (B,S,F,p,f). Each members describe as follows

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Flex Transaction Model
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• Concurrency Control Mechanisms

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Concurrency Control Mechanisms

• The available CCMs can be categorized into
• Locking (2 phase locking)
• Locking and un locking are atomic and mutually
  exclusive for transaction.
• Non locking

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Ways of locking data items

• Simultaneous locking and simultaneous unlocking.

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Incremental locking and simultaneous unlocking.

• It can cause of deadlock

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simultaneous locking and Incremental unlocking.

• It suffer with cascading, which is serious
  time-consuming activity

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Ways of locking data items

• The objective is to minimize the transaction
  waiting.
• It suffer from deadlock and cascading, so it not
  use in reality.

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Non locking based schemes

• Timestamp
• In this method the execution order is defined
  before they begin their execution
• The order of execution is established by
  associating timestamp (integer) to every
  transaction
• Simple timestamp scheme
• Basic timestamping scheme

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Optimistic concurrency control

• It tries to reduce locking overhead by delaying
  lock operation until conflicting of transactions
  are ready to commit.
• It uses three phases read, validate and write.
• Read transaction read the desired data
  completely unrestricted and save it in local
  cache
• Validate in this phase it is determined that
  transaction will not generate an inconsistent
  data and the result is correct
• Write if the validation success, the transaction
  writes the modified data to database, to be
  available for other transaction.
• This approach replace lock overhead with rollback
  overhead in compare with 2PL.

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• Data processing and Mobility

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Mobile Database Systems (MDS)

• MDS Data Management Issues

How MDS looks at the database data?

• Data classification
• Location Dependent Data (LDD)
• Location Independent Data (LID)

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Mobile Database Systems (MDS)

• MDS Data Management Issues

Location Dependent Data (LDD)
The class of data whose value is functionally
dependent on location. Thus, the value of the
location determines the correct value of the
data. Location Data value Examples
City tax, City area, etc.
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Mobile Database Systems (MDS)

• MDS Data Management Issues

Location Independent Data (LID)
The class of data whose value is functionally
independent of location. Thus, the value of the
location does not determine the value of the
data. Example Person name, account number,
etc. The person name remains the same
irrespective of place the person is residing at
the time of enquiry.
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Mobile Database Systems (MDS)

• MDS Data Management Issues

Location Dependent Data (LDD)
Example Hotel Taj has many branches in India.
However, the room rent of this hotel will depend
upon the place it is located. Any change in the
room rate of one branch would not affect any
other branch. Schema It remains the same only
multiple correct values exists in the database.
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Mobile Database Systems (MDS)

• MDS Data Management Issues

Location Dependent Data (LDD)
LDD must be processed under the location
constraints. Thus, the tax data of Pune can be
processed correctly only under Punes finance
rule. Needs location binding or location
mapping function.
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Mobile Database Systems (MDS)

• MDS Data Management Issues

Location Dependent Data (LDD)
Location binding or location mapping can be
achieved through database schema or through a
location mapping table.
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Mobile Database Systems (MDS)

• MDS Data Management Issues

Location Dependent Data (LDD) Distribution
MDS could be a federated or a multidatabase
system. The database distribution (replication,
partition, etc.) must take into consideration
LDD. One approach is to represent a city in
terms of a number of mobile cells, which is
referred to as Data region. Thus, Pune can be
represented in terms of N cells and the LDD of
Pune can be replicated at these individual cells.
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Mobile Database Systems (MDS)

• MDS Data Management Issues

Concept Hierarchy in LDD
In a data region the entire LDD of that location
can be represented in a hierarchical fashion.
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Mobile Database Systems (MDS)

• MDS Query processing

Query types

• Location dependent query
• Location aware query
• Location independent query

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Mobile Database Systems (MDS)

• MDS Query processing

Location dependent query
A query whose result depends on the geographical
location of the origin of the query.
Example What is the distance of LA railway
station from here? The result of this query is
correct only for here.
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Mobile Database Systems (MDS)

• MDS Query processing

Location dependent query
Situation Person traveling in the car desires
to know his progress and continuously asks the
same question. However, every time the answer is
different but correct. Requirements Continuous
monitoring of the longitude and latitude of the
origin of the query. GPS can do this.
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Effect of Mobility on ACID

• Effect of Mobility on Atomicity
• It is difficult to enforcement atomicity in MDS
• Transaction logs are use for atomicity.
• In conventional system that logs find on server
  easily.
• In MDS the logs not easy to access because of
  disconnect mode of MU.

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Effect of Mobility on Consistency

• In conventional system there is only one correct
  value for each data object.
• Mutually consistent state if all copies have the
  exact same value.
• In mobile database the presence of
  location-dependent data defines two types of
  consistency
• Spatial consistency
• Temporal consistency

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Effect of Mobility on Isolation and durability

• In MDS ensure the isolation at the fragment level
  is enough.
• Regional and global durability should be
  considered.

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Effect of Mobility on commit

• Transaction commitment not effected by mobility.
• Because of location-dependent data, a location
  commit is defined.
• A location commit binds a transaction commit to a
  region.
• Example
• Reserve 5 seats in a vegetarian restaurant
  located 1 mile from here

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• Transaction Management in Mobile Database Systems

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Transaction management in mobile database systems

• PCS and GSM used for establish mobile database
• Conventional ACID transaction model was unable to
  satisfactory manage mobile database because of
  following reason
• Hands off, which unpredictable
• Doze mode of mobile unit
• Disconnected mode
• Force disconnection
• Lack of memory and channel resource
• Location dependent data

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Mobile database systems

• MDS provides full database and mobile
  communication functionalities. It allows mobile
  user to initiate transaction from any ware and at
  any time and guarantees their consistency
  preserving execution. In the any kind of failure
  (transaction, system and media), MDS guarantees
  database recovery
• An MDS is a distributed multidatabse
  client/server system based on PCS GSM

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Architecture of MDS
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Mobile database systems

• Fixed Hosted (FH) are general purpose computers
  that interconnected through a high-speed wired
  network.
• FHs are not fitted with transceiver, so they do
  not communicate with MU
• One or more BSs are connected with a Base Station
  Controller (BSC) that coordinate the BSs to
  communicate BSs with FHs and DBS
• To incorporate full database functionality, its
  necessary to incorporate DataBase Server (DBS) to
  PCS or GSM
• DBSs are connected to the mobile system through
  wired line as separate nodes
• Each DBS can be reached by any BS or FH
• A DBS communicates with a MU only through BSs

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Mobile database systems

• Three mode of mobile unit
• Powered mode (not actively listening to the BS)
• Idle mode (doze mode not communicate but
  continuously listening to the BS)
• Active mode (communicating with other party,
  processing data)
• The MDS has multiple DBSs, and a database can be
  distributed by partition or by partial or fully
  replication.
• Special replication must follow the constraints
  of location dependent and location free data

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Different replication types
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Transaction execution in MDS

• Implements parallel processing by fragmenting a
  transaction into a number of subtransactions
  which are then executed at multiple nodes
• The entire execution require a software modules
  called a coordinator
• The coordinator must have
• Direct and continuous communication with other
  nodes
• Theoretically unlimited and continuous power and
  large storage space
• High reliability and availability
• So Between MU, DBS, FH, MSC and BS which one is
  suitable for coordinator?

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Transaction Processing in MDS

• A transaction in MDS can be initiated from a DBS
  or from MU or from both
• It can be processed entirely at the MU or in the
  DBS or a combination of the two
• If process entirely at one node, so coordinator
  have minor role in execution and commitment of
  the transaction
• It is important to note that no other MUs should
  be involved in the execution of transaction
• If an MU initiate transaction, at first check
  that if the transaction can be entirely executed
  locally (at MU), in this case the MU execute and
  commit transaction and send the update for
  install in server and finally send the result to
  the user

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Transaction Processing in MDS

• If it cannot be entirely executed at MU there are
  two options
• Transfer required data items from DBSs to MU
• MU get the desire data from BS
• Send the results to user and update to install in
  server
• Not require of coordinator services
• Significant amount of communication overhead

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Transaction Processing in MDS

• Distribute transaction to a set of nodes
• The MU divides the transaction into a number of
  subtransactions
• Keeps the subtransactions it can execute
• With help of coordinator distribute the rest of
  subtransactoins to a subset of DBSs
• The current BS of the MU becomes the coordinator
  of transaction and manage the execution leading
  either to a commit or abort
• This schema generates less communication overhead
  and database update cost

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Mobility and transaction execution

• The mobility of MU make the job of coordinator
  difficult, following processing scenarios
• Mobile Unit dose not move
• MU moves and the transaction entirely execute on
  MU, this is quite common in mobile computing
• Distributed processing and MU moves, transaction
  originates at a MU and is fragmented to MU and
  DBSs
• The service of coordinator must available
  continuously during the execution of transaction
• This link may be broken when the MU crosses the
  current cell boundary and enters a different cell

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Mobility and transaction execution

• The link can be maintain in two ways
• Static method
• Coordinator not changed, BS1 coordinate
  transaction with help of BS2
• MU inform the new BS of its coordinator

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Mobility and transaction execution

• Dynamic method
• The role of coordinator moves with MU
• The new BS informs all DBSs of the new coordinator

129
Mobile Transaction Model

• Execution model based on ACID transaction
  framework
• Execution Model with Reporting Transaction
• Two-Level Consistency Model
• Pro-Motion Proactive management of Mobile
  Transactions
• Pre-Write transaction Execution Model

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Mobile Database Systems (MDS)

• MDS Transaction Management

Mobile Transaction execution.
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Mobile Database Systems (MDS)

• MDS Transaction Management

Transaction fragments for distributed execution
Execution scenario User issues transactions
from his/her MU and the final results comes back
to the same MU. The user transaction may not be
completely executed at the MU so it is fragmented
and distributed among database servers for
execution. This creates a Distributed mobile
execution.
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Execution Model with Reporting Transaction

• Based on Open-nested transaction
• A parent ACID transaction is set of component
  transactions, where each component can be further
  fragmented in to a number of lower level
  components
• Types of component transaction
• Atomic transaction
• It is an ACID transaction and can be compensated
• It can be commit before parent commit

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Types of component transaction

• Noncompensating component
• It is an atomic component but cannot be
  compensated
• It delegate its updates to its parent
  transaction, which handles the final commit
• Reporting transaction
• Shares its update with the parent transaction at
  any time
• Reports to other transaction by delegating some
  of its current result

134
Types of component transaction

• Co-transaction
• Like reporting transaction but they can
  maintained their execution state, suspend and
  resume
• This schema also identified component as vital
  and none vital, a transaction commit if all vital
  component commit and all non vital component
  commit or successfully aborted
• The reporting and Co-transaction components are
  responsible for all data modification

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Execution Model with Reporting Transaction

• Reporting component always execute on base
  station where co-transaction execute on MU
• When a MU, running a co-transaction, moves and
  register with another BS, the corresponding
  reporting component also move to the BS and the
  communication between reporting and
  co-transaction remain active
• Co-transaction get the most up-to-date values for
  data items
• Reporting component receives update to install in
  the database
• This model does not addressed location-dependent
  data processing issues.

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Two-level consistency Model

• A flexible execution model which considered data
  distribution as a part of the model
• It created clusters of semantically related or
  closely located data which were dynamically
  configured
• Data Cluster A cluster is a set of data with a
  similar set of properties.
• The model also allows mobile user to specify
  conditions for creating clusters
• Useful for local computers who frequently access
  a well-defined set of data items
• Mobile database MDCL1,CL2, , CLn, CLi is a
  cluster.

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Two-level consistency Model

• Cluster consistency
• There exist two kind of consistency
• Intra-cluster consistency refers to consistency
  of data items of a cluster (local consistency)
• Inter-cluster consistency refers to data item
  consistency across the clusters similar to global
  consistency
• The model defines weak transaction and strong
  transaction
• Defines weak read and weak write and refers to
  the normal read as strict read and normal write
  strict write.

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Two-level consistency Model

• Strict write it writes and leaves the database
  in a consistent state
• Strict read it read main database items which
  were written by the last strict writes
• Weak write Write local data (data in cluster).
  This data value becomes permanent only whit
  installed in the main database
• Weak read Reads local data (data in cluster)
  which is written by weak write

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Two-level consistency Model

• Weak transaction a weak transaction is made up
  of only weak reads and writes
• Strong transaction a strict transaction is made
  up of only strict reads and writes
• When a transaction is initiate with user, then it
  fragmented into a number of weak and strong
  transaction

140
Pro-Motion Proactive management of Mobile
Transactions

• This model focuses on the issues introduced by
  disconnections and limited resources
• The model manages the execution with the help of
  compacts and exploits object semantics for
  improving concurrency
• Compacts A compacts is an object which is
  composed of (a) cached data (b) cached data
  access method (c) information about the current
  state of the compact (d) rules of maintaining
  global consistency (e) obligations such as
  deadlines, and (f) an interface for the mobile
  unit to manage the compact

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Compact object structure
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Pro-motion Model

• The server comes to an agreement with the mobile
  unit where a transaction is to be executed
  through a compact
• MU provides its update through the compact
• The creation and removal of a compact is handled
  by database server
• When the MU need data, then send the request to
  server, after that, server creates a compact,
  initials with data and other necessary
  information, and send to MU
• If there already exist compact then server update
  it.

143
Pro-motion Model

• The transaction processing under Pro-Motion model
  has four basic step
• Hoarding the required compacts are prepared to
  manage disconnected execution of transaction
• Connection execution the MU connected to the
  network and the compact manager processes
  transactions
• Disconnected execution the MU disconnected from
  the network, and compact manager processes
  transactions locally

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Pro-motion Model

• Resynchronization the MU, after disconnected
  execution, is reconnected to the server and the
  compact agent reconciles local updates performed
  during disconnected execution with the server
  database

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Mobile Transaction Model

• HiCoMo High commit Mobile transaction Model
• Moflex Transaction Model
• Kangaroo Mobile Transaction model
• Mobilaction Model

146
HiCoMo High commit Mobile transaction Model

• The execution model is mainly for processing
  aggregate data stored in a data warehouse which
  resides in mobile units
• Since the data warehouse resides in mobile units,
  HiCoMo transactions are always initiated on MU
  where they are processed in a disconnected mode
• As a result transaction commitment are quite
  fast.
• The base database resides on the fixed network
• The structured of HiCoMo transaction is based on
  nested transaction model.

147
HiCoMo High commit Mobile transaction Model

• It manipulated by transaction called base or
  source transactions. These transaction initiated
  at the fixed network.
• This require that to install updates of HiCoMo
  transaction, they must be converted to source
  transactions.
• This conversion is done by a Transaction
  Transformation Function

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Moflex Transaction Model

• Its based on Flexible transaction model, and a
  Moflex has 7 components and can be defined as
  Moflex transaction T M, S, F, D, H, J, G

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Moflex Transaction Model

• If the parent subtransaction is compensable and
  processing location-dependent data, then the
  handoff rule forces the subtransaction to abort
  or restart in new cell. A restart can be
  split-restart where the value of the partial
  execution of the partial execution of the
  subtransaction in the last cell is preserved.
• In the case of location-independent
  subtransaction, it further splits in finer
  subtransactions, the last subtransaction that
  occur in the last cell is free to commit.

150
Kangaroo Mobile Transaction Model

• Presented which captured both data and the
  movement of mobile unit
• The model based on a split transaction and
  enforce the ACID properties
• A parent Kangaroo transaction, KT, is composed of
  a number of subtransaction, that each of them an
  ACID transaction, and called Joey Transaction
  (JT) and are local to a base station
• Upon initiation of a Kangaroo transaction, a base
  station creates a JT for its execution
• When the MU migrates to another cell, the BS of
  this cell takes control of the execution of this
  transaction

151
Kangaroo Mobile Transaction Model

• A KT, when initiate by a MU, the initial BS
  immediately creates a JT with a unique identify
  and become responsible for its execution
• When a MU encounters with handoff KT is split in
  two JTs, thus the mobility of a MU is captured by
  splitting a KT
• This JTs executed sequentially, all
  subtransaction of JT1 are executed and committed
  before JT2s

152
Mobileaction Model

• A mobile transaction (MT) can be defined as
• Ti is a triple ltF, L, FLMgt where
• F e1, e2, , en is a set of execution
  fragments,
• L l1, l2, , ln is a set of locations, and
• FLM flm1, flm2, , flmn is a set of fragment
  location mapping where ?j, flmi (ei) li

153
Mobileaction Model

• An execution fragment eij is a partial order eij
  ?j, ?j where
• ?i OSj ? Ni where OSj ?kOjk, Ojk? read,
  write,
• and Nj AbortL, CommitL.
• For any Ojk and Ojl where Ojk R(x) and Ojl
  W(x) for data object x, then either Ojk ?j Ojl or
  Ojl ?j Ojk.

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Mobile Database Systems (MDS)

• MDS Transaction Management

Transaction commit.
In MDS a transaction may be fragmented and may
run at more than one nodes (MU and DBSs). An
efficient commit protocol is necessary. 2-phase
commit (2PC) or 3-phase commit (3PC) is no good
because of their generous messaging requirement.
A scheme which uses very few messages, especially
wireless, is desirable.
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Mobile Database Systems (MDS)

• MDS Transaction Management

Transaction commit.
One possible scheme is timeout based protocol.
Concept MU and DBSs guarantee to complete the
execution of their fragments of a mobile
transaction within their predefined timeouts.
Thus, during processing no communication is
required. At the end of timeout, each node
commit their fragment independently.
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Mobile Database Systems (MDS)

• MDS Transaction Management

Transaction commit.
Protocol TCOT-Transaction Commit On Timeout
Requirements Coordinator Coordinates transaction
commit Home MU Mobile Transaction (MT)
originates here Commit set Nodes that process MT
(MU DBSs) Timeout Time period for executing a
fragment
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Mobile Database Systems (MDS)

• MDS Transaction Management

Protocol TCOT-Transaction Commit On Timeout

• Activities of MUh

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Mobile Database Systems (MDS)

• MDS Transaction Management

Protocol TCOT-Transaction Commit On Timeout
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Mobile Database Systems (MDS)

• MDS Transaction Management

• Activities of CO

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Mobile Database Systems (MDS)

• MDS Transaction Management

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Mobile Database Systems (MDS)

• MDS Transaction Management

• Activities of DBs

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Mobile Database Systems (MDS)

• MDS Transaction Management

• TCOT with Handoff

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• Wireless information Broadcast

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Wireless information Broadcast
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Wireless information Broadcast

• Data Dissemination Mode
• Broadcast Mode in this mode the broadcast server
  periodically broadcast most popular data on some
  wireless channel form which users can listen and,
  if necessary, download if required data. There is
  no uplink channel involved in this mode

166
Wireless information Broadcast

• Data Dissemination Mode
• On-Demand Mode this mode allows a client to
  request specific data which is not available in
  the current broadcast or may never appear in the
  broadcast. The client send the query for require
  data through an uplink channel

167
Wireless information Broadcast

• Data Dissemination Mode
• Hybrid Mode in this mode, broadcast and
  on-demand modes combined.

168
Wireless information Broadcast

• Pull process
• Pull process is user (client) oriented, the user
  assume that the desire in the wireless space, and
  he pulls it by tuning the channel.
• Its user friendly and provides interactive
  capability to users for accessing the information
  through query
• In wireless data dissemination platform, the pull
  approach is resource-intensive. Separate channel
  for sending the query and get the response from
  server are required.

169
Wireless information Broadcast

• Push process
• The server broadcast data on one or multiple
  channels. For example it can push weather info
  and traffic info on the separate channels.
• Client depending upon their data requirements,
  tune the appropriate channel
• Client can not send the specific query to the
  server
• Message indexing can be used for speed up
  broadcast search

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Wireless information Broadcast

• Broadcast Disk

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Wireless information Broadcast

• Broadcast Schedule

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• Any Questions?