Distributed Multimedia Database

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DISTRIBUTED MULTIMEDIA DATABASE

Why multimedia database



Types of multimedia database



Database Organization for Multimedia Application

Distributed architecture provide multiple applications distributed

across network. The different application may access same

database in a independent manner.

Key issues of data organization for multimedia system:

1. Data Independence

2. Common Distributed Database Architecture

3. Multiple Data Server

1. Data Independence

It means the organization of data can be modified without

causing application program to be rewritten.

Key features of data independent designs are:

1. Storage design for multiple application should be

independent.

2. Data definition should be independent.

3. Data modification & alteration should be independent.



4. Data recovery should be independent.

2. Common Distributed Database Architecture

The combination of data and application provides the opportunity

to employ common distributed database architecture.

Key features are:

1. The ability of multiple data to coexist in the system.

2. Uniform access by clients.

3. Single point for recovery of each database server.

4. Data re-organization for multiple requirements.

5. Tunability , expandibilty and creation of object classes.

3. Multiple Data Server

• When multiple users gain access to same resources, their

exist a bottleneck problem since server cannot fulfill all

demands.

• This problem is overcome by setting multiple data servers

that keeps copy of same resources.

• Not all objects are duplicated but only objects with heavy

demand are replicated on multiple servers.

• Replicated objects are not identical but they are intended to

be identical.

Transaction Management for multimedia System

• Transaction is defined as the sequence of events that starts

when user makes a request to create , display and playback

hypermedia documents.



• Transaction is complete when the user release the

hypermedia documents.

• During the course of the transaction the user may add new

elements.

• Transaction manager handles the conflict, when two user

attempts to read or write same data record and manages

the sequence of events.



There are three different action TCO can perform

• Display what is available

• Wait until all components get available

• Terminate the transaction

The ORB (Object Request Broker) response to the request fromthe TCO, and playback information to the HD(Hypermedia display)

under the control of TCO(Transaction control object).

Other objects are needed for the full scheme.

Managing Hypermedia Records as Object

Hypermedia records or documents contain multimedia

information object within them.

Hypermedia records are stored :

• As a binary large object (BLOB) , in a relational database.

• As an object , in object-oriented database.



The multimedia objects are not stored or embedded in records

but a reference to that object is embedded and the actual object

is linked in its database.

Information items that are included in a reference :

Types of object i.e. audio, video, text.

Unique object ID for multimedia objects.

File name , which can later be identified after being stored

in a database.

Size of the objects.

The network server where it was created.

Time and date of creation.

Application or player require to display the object.

Indexing information for indexed object etc.

The objects can either be linked or embedded.

• The linked object contain data needed to represent the

object and a pointer to the actual file that contain the

original data.

• Embedded object contain the object along with the

information needed to edit the object.

In this types, editing is done on embedded object and the

original copy of the object is not effected when embedded copy is

edited or manipulated.



Linked Objects

Embedded objects



Difference between linked and embedded objects

• Embedding causes the object to be stored with container

documents, while linking stored it in separate object servers.

• Embedded object edits in embedded copy not in original

copy.

Interserver Communication

In a distributed system, multiple servers are used to provide the

users with fast access of information.

This information's are maintained on servers that are connected

locally to the servers and are shared by every workstation.

Interserver communication can be defined by some of the design

requirements i.e. :-

1. Object Replication

2. Object Distribution

3. Object Recompilation



4. Object Management

• Object Replication : Managing replicated copies object in

efficient manner.

• Object Distribution : Access objects that are spread

throughout the organization.

• Object Recompilation : Require complex database records to

store object that are accessed.

• Object Management : Require for efficient use of system and

resources.

Types of communication between different servers :1. Obtain a token, from object nameserver for creating a new

multimedia object.

2. Search object location from object class directory and least

cost route to access the object.

3. Perform a shared read lock on the object.

4. Replicate a copy of the object, update the object nameserver directory.

5. Copy an object for non persistent (temporary) use.

6. Set exclusive lock for editing purpose.

7. Pause the retrieval of an object to support a user action.

Object Server Architecture

Key elements of architecture :

• Multimedia application

• Common Object Management API

• Object Request Broker

• Object Nameserver

• Object Directory Manager



• Object Server

• Object Manager

• Network Manager• Object data store

Fig: Object Server Architecture

Multimedia application : It can be any application i.e.

e-mail, hypermedia, etc that are design to operate

on common object management API.

Common Object Management API : It provide library of

function (like search, creation, manipulation) that the

application can call.

Object Request Broker : It perform functions like

1. Object Recompilation (presentation of complex object)

2. Playback Control (how object should be transferred)

3. Format Conversion (according to storage format, client

application format)

Object Nameserver : It provides availability of information

object & list of object server on which it is located.



Object Directory Manager : Updates the directory when

changes takes place.

Object Server : It is a subsystem for storing and retrieving

objects on demand.

Object Manager : It consist of number of object classes that

perform number of services i.e. object retrieval, replication,

migration, transaction management, lock management.

Network Manager : It is essential for interaction between

objects over the network. It maintains and evaluate cost

based routing table.

Object data store : It is used for storage media for differentmultimedia objects.

Object Identification

There are large number of objects in a multimedia system

that are stored on different servers. Thus each object must

have unique identity.

Object identification allows uniquely identifying all objects inenterprise-wide network. We use “naming scheme” for this

purpose.

It consist of :

• Object Identity

• Identification Method

•

Identities of Copied & Merged Objects• Object Identity in Network

• Object Identity : The property of an object that distinguish it

from other objects. This property remains same throughout



the life of object despite of modification. Unique object

identifier “Object ID” is used for this purpose.

• Identification Method : Object identifier must be unique for

time dimension (i.e. does not change with time) & location(in network) .

Components of object identification method :

o Network domain name

o Address & server ID of name server node that created the

ID

o A time stamp of creation time

o An object class identifier

• Identities of Copied & Merged Objects : No changes should

occur in object & its identity while copying an object for

replicated purpose. After copying the new object (replicated

object) must have a unique identifier.

• Object Identity in Network : Unique identity across the

network ensures that object can be access from anywhere

within the network, despite of its current location.

Object Revision Management

When multimedia objects are modified, the new copy is

generates from the older copy i.e. new object version is

created from older version. Thus versioning of object is

important characteristics of the object-oriented system.

Versioning :Each objects may have one or more servers.

Version management scheme has two attributes :

1.Version number

2. Object ID



Two types of versioning objects are :

1. Association object

2. Aggregation object

Association object : It allows collecting random object ID as a set,

which may represent the version tree.

Aggregation object : It is a meaningful collection of object IDs with

some display information.

Object Directory Services

All the multimedia objects in a LAN is controlled by multimedia

object directory manager i.e. “name server”. It maintains a entry

for each multimedia object.

Each object has a unique object ID.

“Name server” provides object directory services, maintain a

database, object directory which list all multimedia object.

It manages

• changes

• replication

• synchronization of replicated object directory

Locking of object : Object manager ensure that object in use

should not be deleted. It should provide a centralized lock to

prevent deletion of object in use.

Directory Synchronization : Object manager should check the

database on a periodic basis in order to keep track of

multimedia objects in use.



Optimizing Network Location Of Object

Location of multimedia object (such as audio, video, text)

becomes an important issue.

For this purpose we use a data processing system and allocate

unique ID for each object.

The data processing system may be a shared system across

the enterprise but may have restricted access to individual

users in each department.

Our motto here, is automatic relocation of objects to achieveload balancing.

Few things to be considered for load balancing are :

1. Database should contain the object & relocation parameter.

2. Creator of the object must be known.

3. How frequently the creator use the objects.

4. How many times the objects is being accessed by the users.

5. Optimum storage volume for each object in the server.

Multimedia Object Retrieval

Multimedia object manager, manages all request by different

application and controls functions like :

-

Retrieving multimedia object- Storing multimedia object

- Editing multimedia object

This request is channeled through the object request broker.



The multimedia object directory keeps the track of all multimedia

objects in use.

Services provided by the Multimedia Object Manager :

• When a user click on play button , the application request

the manager for rendering the object.

• If new object is created , manager assign a unique ID to

the object.

• The manager maintains directory and track of the

multimedia object.

•

The manager is also responsible for load balancing.Data Structure Maintained by Multimedia Object Manager :

• Multimedia directory database

• Dynamic lock status on multimedia objects

• It maintain data structure for all replicated objects.

Object Recompilation for output : The multimedia objects are

stored in different databases and different servers. So a

mechanism is required to access all sub objects. When users

reads in a database records.

Using Object Request Brokers: ORB is used to handle all

requests. It response to the request from the different application

and perform necessary processing of data.

Retrieval Conflicts: Three condition for this are:

• Single user access document from local servers.

• Multiple users gain access to same documents.

• One user delete a document while it is in use by other user.



Database Replication Techniques

Three goals to maintain a database are:

• Sharing all data objects by all users on the network

• Providing acceptable performance to all users

• Allowing all users to update the database.

In order to meet this goal data duplication is achieved but it need

to keep all the copies synchronized which is not possible all the

time. So database replication is achieved i.e. to allow each copy

of the database to be modified as needed.

Types of database replication :

1. Round Robin Replication: Each database copy replicates with

the rest in round robin fashion. But the problem is if servers

fails, the cycle is broken & replication stops.

2. Manual Replication : It require a database administrator to

define the server which object it should replicate.

3. Scheduled Replication : All database server will replicate attheir scheduled time even if database server is unavailable.

This technique is used when usage is low & network load is

lower.

4. Immediate Replication : It is used where the multimedia

object is expected to be required almost immediately.

5. Replication On Demand : It replicate objects on demand

basis only when they are required by a user. In this serverfirst check its own database and then master database copy

for the object to be replicated.

6. Predictive Replication : In this , algorithm develops a

prediction criteria (like type of database, priority of object,

type of object etc) to select a object for replication.



7. Replicating Reference : In this only reference to a replicated

object is replicated.

8. No Replication : It is used when user view a multimedia

object and knows that there I s no need of replication.

Data Structure Maintained :

• Object Location

• Status Request

• Replication List

• Replication Record

Object Migration Scheme

Three important reason for this approach are :

1. How application locate & retrieve an objects.

2. Which server should retain copies of multimedia objects.

3. What is the planned migration path to off-line media.

The first problem is solved by “object directory manager” . It keeps track of

each object and all related information like migration status , retrieval of

object , load balancing , estimate time for retrieval etc.

Second problem is solved by using a load balancing algorithm which

determine the migration of object from one server to another.

Third problem is solved by assuring that the offline objects that are to be

migrated are remain referenced by the object name server and can be located

on off-line media using some identification technique.

Optimizing Object Storage

Techniques used for optimizing data storage for multimedia objects are :

1. Optimizing Servers by object type



2. Automatic load balancing across servers

3. Versioned object management

Optimizing Servers by object type : In this approach each object type is

assigned with a dedicated server. The object server is designed to providespecialized services for specific object.

Automatic load balancing across servers : It can be achieved by programming

a replication algorithm to count each copy of replicated object. When the

count falls below a certain mentioned threshold , the object is removed from

the server.

Versioned object management : The storage become tough when multiple

version need to be stored. So techniques are used to store only the “changes”

that occur in new version and not the whole new copy.

Documents

Distributed Multimedia Database