Download - A Survey on Context-Aware Computing : Past, Present, and Future

A Survey on Context-Aware Computing: Past, Present, and Future

Center for E-Business TechnologySeoul National University

Seoul, Korea

Sang-keun Lee

Intelligent Database Systems LabSchool of Computer Science & EngineeringSeoul National University, Seoul, Korea

Copyright 2008 by CEBT

Motivation

Context-Aware System


History of Context-Aware Computing :Context Definition

Term ‘Context-aware’ appeared in Schilit and Theimer(1994) Authors describe context as location, identities of nearby peo-

ple, objects, and changes to those objects Ryan et al. (1997) referred to context as the user’s location,

environment, identity, time Day (1998) : the user’s emotional state, focus on attention,

location, and orientation, date and time, as well as objects and people in the environment

Dey and Abowd (2000) Any information that can be used to characterize the situation

of entities that are considered relevant to the interaction be-tween a user and an application, including the user and the ap-plication themselves


History of Context-Aware Computing :Application & System, Context Model

Active Badge Location System (Wang et al., 1992) One of the first context-aware systems Forward phone calls to a telephone close to the user

Couple of location-aware tour guides Abowd et al., 1997; Sumi et al., 1998; Cheverst et al.,2000 Providing information according to the user’s current location

Watson Project (Budzik and Hammond, 2000) W3C, RDF available (2000) IntelliZap (Finkelstein, 2001) Context Toolkit (Dey and Abowd, 2001)

p2p architecture + centralized discoverer, attribute-value tuple/XML - Context aggregation/interpretation, historical context data, Context Ownership (Privacy)

Hydrogen (Hofer, 2002) local/remote context, Object Oriented Model, process higher-level context

abstraction in application layer



Gaia project (Roman’s) Extends operating system contepts to include context-awareness 4-ary predicates in DAML+OIL, context processing is based on first-order

logic operation Graphical Context Model: ORM (Hendricksen, 2003) Context Managing Framework (Koripaa, 2003)

Centralized server CoBrA- Context Broker Architecture (Chen, 2003)

COBRA-Ont(Ontology Model), Inference Engine, historical context data, Broker federation – Avoiding bottleneck Context Knowledge base – You can assert, delete, modify, query the stored

data(API) Flexibile policy language to control context access called Rei (privacy)

2004 W3C, OWL available



Markup scheme model: Composite Capabilities/Preference Profile (CC/PP) (W3C, 2004)

SOCAM(Service-Oriented Context-Aware Middleware) (Gu, 2004) Upper ontology, Domain-specific Ontology

CASS (Fahy and Clarke, 2004) CORTEX (2004)

Based on sentient object model – sensor fusion to manage uncertainty of sensor data

Graphical Context Model: Context Modeling using UML (Sheng and Benatallah, 2004)

CoCA (Ejigu, 2007) Enhanced CoCA (Ejigu, 2008)

Using a hybrid context management model – Relational Database, Ontology Tools

Heuristics for better performance


History of Context-Aware Computing:Sensor Definition

Burnett (2003) and Gustavsen (2002) External and internal

Hofer et al. (2002) Physical and logical

Semantic Tech & Context - 7

Context that can be measured by hardware sensors, i.e,., locationa, light, sound, movement, touch, temperature or air pressure

Context that can be captured by user interactions, i.e., the user’s goals, tasks, work context, emotional state

Easier to sense


The History in Summary Specific Context Definition to General Context Definition Non-Flexible Context Models to Flexible and Extensible

Context Model Domain-specific Applications to General Frameworks


Categories of Context Aware Applica-tions Schilit (1994)

Proximate Selection– A user interface technique where the located-objects that are nearby are emphasized or

otherwise made easier to choose Automatic Contextual Reconfigurations

– Reconfiguration is the process of adding new components, removing existing components or altering the connections between components

Contextual Information and Commands– Queries on contextual information can produce different results according to the context in

which they are issued Context-Triggered Actions

– Context-triggered actions are simple IF-THEN rules used to specify how context-aware systems should adapt

Sang-keun Lee Context-Aware / Personalized Contents Push Seamless Device Switching Automatic Device Configuration Decision Support/Suggestion Context Aware User Interface

11Context-aware computing applications (Schilit, B.; Adams, N.; Want, R.)Mobile Computing Systems and Applications, 1994. Proceedings., Workshop onVolume , Issue , 8-9 Dec 1994 Page(s):85 - 90


An Example of Domain-dependent Applications: Cyberguide : A mobile context-aware tour guide (1997)

Goal know where tourist is, and what she is looking for predict and answer question she may pose provide interaction with other people and environment


Design Principles – Architecture Chen (2004) presents three different approaches on how to acquire contextual in-

formation Direct sensor access – devices with sensors locally built in Middleware infrastructure – hiding low-level sensing details, more extensible Context Server – multiple clients access to remote data source

Winograd (2001) Widgets – a software component that provides a public interface for a hardware sensor,

hiding low-level details of sensing, managed by widget manager Networked services – more flexible, discovery techniques are used, not as efficient as a

widget architecture but provides robustness Blackboard model – data centric view, simplicity of adding new context sources (easy

configuration) Architecture Style

Peer to Peer– Limitation of Memory Resource, CPU Performance– Only uses local built-in sensors

Centralized Approach– Robustness

Baldauf, M., Dustdar, S., and Rosenberg, F. 2007. A survey on context-aware systems. Int. J. Ad Hoc Ubiquitous Comput. 2, 4 (Jun. 2007), 263-

277. DOI= http://dx.doi.org/10.1504/IJAHUC.2007.014070


Hydrogen (2002) Framework Architecture

Three layer– Application layer– Management layer

Providing and retrievingcontexts and sharingcontext informationwith other devices usingP2P communication

– Adaptor Layer Separating context storing, sensing from other layers Responsible to get information from sensors Providing same context information to multiple applications

All application have access to all context data by querying the Con-textServer

All layers are located on one device– Robust against network disconnections, Peer to Peer

Object-oriented Context Model

Copyright 2008 by CEBT Semantic Tech & Context - 15

SOCAM Architecture (2004) Context providers, Context interpreter, Context database, Context-aware services, and Service

locating service Architectural Requirements

A common context model that can be shared by all devices and services A set of services that perform context acquisition, context discovery, context interpretation and

context dissemination Upper/Domain-specific Ontology

Context Providers

• Acquire context from sources

Context Interpreter

• Provides logic reasoning

Context Database

• Stores context ontologies

Context-aware Services

• Adapt the way they behave

Service Locating Service

• provides a mechanism where Context Providers and the Context Interpreter can advertise their presence


The Context Fabric (2004) Primarily concerned with pri-

vacy rather than with context sensing and processing

provides an architecture for pri-vacy-sensitive systems, as well as a set of privacy mechanisms that can be used by application developers

Previous work on privacy has tended to focus on anonymity or on keeping information from hackers

Confab’s focus is in empowering people with choice and informed consent, so that they can share the right information, with the right people and services, in the right situation

Copyright 2008 by CEBTIDS Lab. 17

The CoCA Service Platform (2007)

Interface Manager Manages a UI and interface between the CoCA platform and other modules

Data Source Responsible to provide necessary data to the core service (GCoM)

Core Service Responsible to provide the core context aware service after reasoning on the com-

ponents Supplementary Service

Knowledge discovery & Collaboration service

The Platform aims at acquiring and utilizing context information to provide appropriate services E.g) A cell phone is always set to

vibrating mode when its holder is in the libraryIt filters and sends use-

ful contexts to the con-text repository

It Keeps the rules in the rule repository

It consists of domain depen-dent/independent ontology

Reasoning -> Decision & ActionInterpretation, Aggregation


The Enhanced CoCA Service Platform (2008)

Enhanced version of CoCA Combine the best of the relational approach and ontology approach Selective feature of loading only relevant context data into the rea-

soner using heuristics


Summary: Existing systems and frameworks

Baldauf, M., Dustdar, S., and Rosenberg, F. 2007. A survey on context-aware systems. Int. J. Ad Hoc Ubiquitous Comput. 2, 4 (Jun. 2007), 263-

277. DOI= http://dx.doi.org/10.1504/IJAHUC.2007.014070


Criteria

Henricksen, K., Indulska, J., McFadden, T. and Balasubramaniam, S. (2005). Middleware for distributed context-aware systems. In: Robert

meersman and Zahir Tari et al International Symposium on Distributed Objects and Applications (DOA), Agia Napa, Cyprus, 31 October - 4 No-

vember, 2005.


Discussion Does a context-aware system bother users?

MS Office Assistant Clippy Three Levels of Interactivity

– Personalization The majority of users use the default setting of change a small subset of the possible features

– Passive Context-awareness Presenting the updated context to the user Let the user specify how the application should change Ex) mobile phone prompts the user with information about the time zone change

– Active Context-awareness Changing the content autonomously on the basis of measured sensor data Ex) Mobile phone that changes its time autonomously by new time zone

The authors conclude that people are willing to give up partial control if the reward in usefulness is great enough

How could we deal with the imperfect/probabilistic context data? Fuzzy Logic Context Data Abstraction

What could be the Killer Application? What could we mine from the log data?

Support Rules

Peer to Peer vs. Centralized System

L Barkhuus, A Dey, Is Context-Aware Computing Taking Control Away from the User? Three Levels of Interactivity Examined,2003


Layered Conceptual Framework with Core Components

Foundation Layer:SensorsData/Rule MiningRelational DatabaseNetwork

Semantic Technology Layer:Ontology RepositoryInference Engine

Service & Application Design Layer:

Context-Aware Services:

Context Acquisition DeviceCommunication

Data Management & Mining

Context OntologyModeling

Context Fusion & Abstraction

Rule based Action Triggering

Ontology DataStorage

& Management

Low-levelData Modeling

Context-Aware Personalized Contents Push

Seamless Device

Switching

Automatic Device

ConfigurationDecision Support

& SuggestionContext Aware User Interface

UbiquitousIntelligentSeamless

Domain-specific Context Data

ModelingRule

DefiningService

Algorithm Implementation

Privacy & Security Policy

Defining

Private Scalable


Conclusions We talked about

Motivation History of Context-aware Computing Categories of Context-aware Applications Design Principle Examples of Context-aware Systems Criteria & Discussion

What will be the future Context-aware System? A Context-aware system with

– Better scalability and performance– Utilizing historical context data (Rule mining, ...)– Better Security policies and privacy protection– Virtual and logical sensor support– Standard communication protocol and context model

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