A System Architecture for ContextAware Applications

1
A System Architecture for Context-Aware
Applications

• By Manasi N. Joshi
• Plan B Presentation
• 7thSeptember 04
• University of Minnesota, TC

2
Overview

• Motivation
• Previous Work
• Context and Context-Awareness
• Our Framework
• Examples
• Future Work

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Motivation

• Computers are divorced from reality
• Unaware of who, where, and what around them
• Computers take extremely limited input
• Context-Aware Computing
• Making computers more aware of the physical and
  social environment

4
Previous Work

• Resource discovery and binding using XML
• Resource Providers
• Resource Server
• Clients
• RDD (Resource Description Document) schema with
  tags for
• Property (Attribute)
• Operation (Method)
• Message (Parameter)
• Java RMI used for binding

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Example SampleRdd.xml

• lt?xml version"1.0"?gt
• ltRDD xmlnsxs"http//www.w3.org/2001/XMLSchema-i
  nstance" xsnoNamespaceSchemaLocation"RDD.xsd"gt
• ltpropertygt
• ltpidgtcameralt/pidgt
• ltnamegtResolutionlt/namegt
• ltvaluegt3lt/valuegt
• ltdescriptiongtCamera with 3 Mega Pixel
  Resolution lt/descriptiongt
• lt/propertygt
• lt/RDDgt

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Overview

• Motivation
• Previous Work
• Context and Context-Awareness
• Our Framework
• Examples
• Future Work

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Context and Context-Awareness

• Context is any information that can be used to
  characterize the situation of an entity
• A system is context-aware if it uses context to
  provide relevant information and/or services to
  the user, where relevancy depends on the users
  task
• - Anind. K. Dey

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Context-Based Service Discovery and Binding

• Extended Schema
• Proposed System Components
• Provider (PROV)
• Discovery Service (DS)
• View Manager (VM)
• Context Manager (CM)
• Application (APPLN)

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Context Difficult to use

• Acquired from non-traditional devices (GPS,
  Active Badge, presence sensors)
• Has to be abstracted to be useful for a
  particular application
• Gets acquired from heterogeneous sources can
  have uncertainty
• Dynamic changes in environment have to be
  sensed and adapted to in real time

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Schema

• Application Client Resource Provider

C1
ReqApp1.xml
Description.xml
C2
ReqApp2.xml
C3
ReqApp3.xml
NO CONTEXT
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New Schema(ApplicationOuter)

• lt?xml version"1.0"?gt
• ltCONTEXT xmlnsxs"http//www.w3.org/2001/XMLSchem
  a-instance" xsnoNamespaceSchemaLocation"Requirem
  ent.xsd"gt
• ltcontextgt
• ltidgtaristotle.cs.umn.edult/idgt
• ltresReqFlgtReqApp1.xmllt/resReqFlgt
• lt/contextgt
• ltcontextgt
• ltidgteverest.cs.umn.edult/idgt
• ltresReqFlgtReqApp2.xmllt/resReqFlgt
• lt/contextgt
• ltcontextgt
• ltidgt128.101.32.72lt/idgt
• ltresReqFlgtReqApp3.xmllt/resReqFlgt
• lt/contextgt
• lt/CONTEXTgt

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ReqApp1.xml(ApplicationInner)

• lt?xml version"1.0"?gt
• ltREQUIREMENT xmlnsxs"http//www.w3.org/2001/XMLS
  chema-instance" xsnoNamespaceSchemaLocation"Requ
  irement.xsd"gt
• ltResourcegt
• ltcategorygtspeakerlt/categorygt
• ltbindingPolicygtrebindlt/bindingPolicygt
• ltmatchSpecgtalllt/matchSpecgt
• ltspecgt
• ltattributegtVolumelt/attributegt
• ltmatchValuegt
• ltidgtrangelt/idgt
• ltvaluegt65lt/valuegt
• ltvaluegt110lt/valuegt
• lt/matchValuegt
• lt/specgt
• lt/Resourcegt
• lt/REQUIREMENTgt

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New Schema (ExampleSPEAKERI.xml)

• lt?xml version"1.0"?gt
• ltRESOURCE xmlnsxs"http//www.w3.org/2001/XMLSche
  ma-instance" xsnoNamespaceSchemaLocation"Resourc
  e.xsd"gt
• ltprovidergt ltcategorygtspeakerlt/categorygt
  ltlookupNamegtSPIlt/lookupNamegt
• ltspecgt
• ltattributegtRMILocationlt/attributegt
  
• ltmatchValuegt ltidgtalllt/idgt
  ltvaluegtaristotle.cs.umn.edult/valuegt
  lt/matchValuegt
• lt/specgt
• ltspecgt
• ltattributegtRMIPortlt/attributegt
• ltmatchValuegt ltidgtalllt/idgt
  ltvaluegt22222lt/valuegt lt/matchValuegt
• lt/specgt
• ltspecgt
• ltattributegtVolumelt/attributegt
• ltmatchValuegt ltidgtsubsetlt/idgt
  ltvaluegt70lt/valuegt ltvaluegt90lt/valuegt
  ltvaluegt120lt/valuegt lt/matchValuegt
• lt/specgt
• lt/providergt
• lt/RESOURCEgt

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New Schema Features

• Flexibility in Attribute-Value Pairs
• ltmatchSpecgt
• (all, some, none)
• ltspecgt, ltmatchValuegt
• (all, subset, range, rangebar)
• Incorporation of context
• Application client described at two levels
• Context Level ltcontextgt
• Requirement Level

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System Architecture
Context Manager
Provider
Application
Discovery Service
View Manager
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Discovery Service Starts Running
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Provider Registers With DS
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Application Registers With VM
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CM Sends Context Trigger To VM
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Context-Aware Discovery By DS And Response Back
To VM
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Get Current Binding Status
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Overview

• Motivation
• Previous Work
• Context and Context-Awareness
• Our Framework
• Examples
• Future Work

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Test Example I Context-Sensitive Printing

• Two lists of hosts maintained (running Linux)
• Distributed Systems Lab Hosts (Room 5-248)
• Grad Lab Hosts (Room 2-216)
• Resource Providers (Printers)
• Context Trigger Host Name
• Result A document gets printed on one of
• nexus (printer in 5-248)
• grad (printer in 2-216)

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Test Example II Context-Aware Music

• JMF used to run media (music) using Java
• Resource Providers (A pair of speakers)
• Context Trigger Host Name
• Result Song starts playing through a matched
  pair of speakers for a host

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Timings All in ms
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Existing Limitations

• Printing
• Does not work with ssh like mechanisms
• Music
• No check for provider availability
• A fixed location of song no buffering concept

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Overview

• Motivation
• Previous Work
• Context and Context-Awareness
• Our Framework
• Examples
• Future Work

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Future Work

• Binding Policy
• Permanent Binding or Context-based
• Shared Binding or Private Binding
• Context-awareness on Provider Side
• Nature of Contexts
• Providers (not classified as services)

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Continued

• Interoperability
• Services, devices, Context Detectors
• Need standard data formats, protocols, and
  frameworks (Web-Services)
• Varying capabilities of sensors, services, and
  devices
• Security
• In schema (SAML)
• In API

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