context aware systems - seminar report

8/9/2019 Context aware Systems - Seminar Report

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CONTEXT-AWARE COMPUTING

RUBY ELJUSE

Seventh Semester

Department of Computer Science

M G College of Engineering

[email protected]

Abstract-There is a growing interest in the use of context-

awareness as a technique for developing pervasive

computing applications that are flexible, adaptable, and

capable of acting autonomously on behalf of users.

However, context-awareness introduces various software

engineering challenges, as well as privacy and usability

concerns. In this paper, I present technical aspects of

context-aware computing (systems), a conceptual

framework, its few applications and some drawbacks.

I. INTRODUCTION

With the appearance and penetration of mobile devices

such as notebooks, PDAs, and smart phones, pervasive (or

ubiquitous) systems are becoming increasingly popular

these days. The term pervasive introduced first by Weiser

(1991) refers to the seamless integration of devices into the

users everyday life. Appliances should vanish into the

background to make the user and his tasks the central focus

rather than computing devices and technical issues. One

field in the wide range of pervasive computing is the so-

called context-aware systems.

Several authors gave definitions for the term context. One

of the accurate definitions is given by Dey and Abowd.

They refer to context as

any information that can be used to characterize the

situation of entities (i.e., whether a person, place or

object).

Another definition for context is

the set of environmental states and settings that either

determines an applications behavior or in which anapplication event occurs and is interesting to the user.

The context is further classified into two external and

internalcontexts. The external refers to context that can be

measured by hardware sensors, i.e., location, light, sound,

movement, touch, temperature or air pressure, whereas the

internal is mostly specified by the user or captured by

monitoring user interactions, i.e., the users goals, tasks,

work context, business processes, the users emotional

state. Most context-aware systems make use of external

context factors as they provide useful data, such as location

information.

II. HISTORY

The concept context-aware computing is emerged out of

ubiquitous computing research at Xerox PARC in the early

1990s. The term context-aware was first b Schilit and

Theimer in 1994 in their paperDisseminating Active Map

Information to Mobile Hosts where they describe a model

of computing in which users interact with different mobile

and stationary computers and classify context-aware

systems as one that can adapt according to its location of

use, the collection of nearby people and objects, as well as

the changes to those objects over time over the coarse of

the day.
mailto:[email protected]:[email protected]


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III.CONTEXT-AWARE COMPUTING

Context-aware computing refers to a general class of

mobile systems that can sense their physical environment.

Otherwise context-aware systems are able to adapt their

operations to the current context without explicit user

intervention and thus aim at increasing usability and

effectiveness by taking environmental context into account.

Such systems are a component of a ubiquitous computing

or pervasive computing environment. Three important

aspects of context are: (1) where you are; (2) who you are

with; and (3) what resources are nearby. Context-aware

computing are categorized into two types based on the way

of using the context i.e., as active context or passive

context. Active context influences the behavior of the

application. Passive context is a context that is relevant but

not critical. The two types are:

Active context awareness: an application automatically

adapts to discovered context, by changing the applications

behavior.

Passive context awareness: an application presents the new

or updated context to an interested user or makes the

context persistent for the user to retrieve later.

IV. CONCEPTUAL FRAMEWORK

The following layered conceptual architecture, as depicted

in Figure, augments layers for detecting and using context

by adding interpreting and reasoning functionality.

Application

Storage/Management

Preprocessing

Raw data retrieval

Sensors

Figure: Layered conceptual framework for CWC

The first layer consists of a collection of different sensors.

It is notable that the word sensor not only refers to

sensing hardware but also to ever data source which may

provide usable context information. Concerning the way

data is captured; sensors can be classified in three groups:

Physical sensors: The most frequently used type

of sensors are physical sensors. They are actually

hardware sensors for capturing physical data such

as light, noise, temperature etc. Many hardware

sensors are available nowadays which are capable

of capturing almost any physical data. Table

shows some examples of physical sensors.

Virtual sensors: Virtual sensors source context

data from software applications or services. For

example, it is possible to determine an

employees location not only by using tracking

systems (physical sensors) but also by virtual

sensors. Other context attributes that can be

sensed by virtual sensors include, e.g., the users

activity by checking for mouse movement and

keyboard input.

Logical sensors: These sensors are the

combination of both physical and virtual sensors.

They are used for solving higher tasks. For

example, a logical sensor can be constructed to

detect an employees current position by

analyzing logins at desktop PCs and a database

mapping of devices to location information.

The second layer is responsible for the retrieval of raw

context data. It makes use of appropriate drivers for

physical, virtual and logical sensors.

The third layer is thepreprocessing layerand is responsible

for reasoning and interpreting contextual information. The

preprocessing layer is not implemented in every context-

aware system but may offer useful information if the raw

data are too coarse grained. In this layer, single context

atoms can be combined to high level information and this

process is called aggregation orcomposition.


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Table: Commonly used physical sensor types

Type of

context

Available sensors

Light Photodiodes, color sensors, IR and UV

sensors etc.

Visual context Various cameras

Audio Microphones

Motion,

acceleration

Mercury switches, angular sensors,

accelerometers, motion detectors,

magnetic fields

Location Outdoor: Global positioning System

(GPS), Global System for Mobile

Communications (GSM); Indoor: Active

Badge system, etc

Touch Touch sensors implemented in mobile

devices

Temperature Thermometers

Physical

attributes

Biosensors to measure skin resistance,

blood pressure

The fourth layer is Storage and Management layer whichorganizes the gathered data, and offers them via a public

interface to the client. Clients may gain access in two

different ways, synchronous and asynchronous. In the

synchronous manner, the client sends a message requesting

some kind of offered data and pauses until it receives the

servers answer. The asynchronous mode, the client sends

messages to server and performs other operations rather

than waiting for the servers response. In the majority of

cases the asynchronous approach is more suitable due to

rapid changes in the underlying context.

The client is realized in the fifth layer, the Application

layer. The actual reaction on different events and context-

instances is implemented here.

V. APPLICATIONS

There are many applications evolved from the concept of

context-aware computing. From these applications, only

three important ones are listed below.

A. Xerox PARCTAB:

The PARTAB is a small hand held device which

uses an infrared-based cellular network for

communication. The tab acts as a graphics

terminal. For input, the tab has three finger-

operated buttons on the grip and a touch sensitive

screen. For output, the tab has a 128x64 pixel

display and a piezo-electric speaker. It was

developed fromXerox Palo Alto Research Center.

It shows information about user location, people

and hardware nearby etc. That is, it helps the usersto find the nearby local resources, for example,

nearest printer. PARCTAB can also be used as a

remote control which controls changed depending

on context lights, temperature, TV, radio, moving

display windows. The problems with PARCTAB

are its small size, small window and more power

consumption.

Figure: Xerox PARCTAB

B. Active Badge System:


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It is one of the first context-aware systems. It was

developed from Olivetti Research Lab in 90s.

The application area of active badge system is

how to locate a person. For example, at a hospital

if a doctor needed for an emergency or in an

office if a person missing from a meeting.

Another application is call forwarding. In call

forwarding, the location context is presented to

the receptionist, who routinely forwards the

telephone calls to the destination users nearest

phone. The working of active badge system is: it

emits unique code or IR signals at every 15

seconds. This code or signals is picked up by the

sensor network in the building. The master station

(work station) polls sensors for finding the

location of users (sightings) and thereby providing

location of users.

The drawbacks of active badge system are:

Less battery power

Solution: provide short signals and

after every 15 seconds, switches off

automatically.

Privacy concerns

Solution: Badge owners could just

take it off and leave it on their desk.

Figure: Active Badge System

C. Cyber Guide:

Cyber Guide is a mobile context-aware tour guide

(indoors and outdoors). It was developed by

Georgia Tech. It provides information services to

a tourist about users current location; for example

user can find directions, retrieve background

information. The travel diary is automatically

recorded using the history of where a tourist has

traveled over time, and it is used by the system tomake suggestions on places of interest to visit.

The location information is collected by GPS for

the outdoor version, and by an infrared (IR)

positioning system, for the indoor version.


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Figure: Cyber Guide

Figure: Cyber Guide Map Information (Outdoor)

VI. DRAWBACKS OF CONEXT-AWARE SYSTEMS

There are several drawbacks for context-aware systems and

they are listed below.

A) General: security, privacy.

Context-aware systems never provide privacy to the users

since it is used for location specification. Also no security

measures are provided for storing the contextual

information in such systems.

Wireless: Range, signal detection.

B) Higher energy consumption and require more data

storage and data processing.

C) More expensive.

D) Context awareness: Accuracy.

This includes two issues: one is if the context data is

missing and second one is if the context information is

inaccurate. In the first issue, the operation is just dropped

out and in the second one, the context-aware systems provide throughput according to the gathered context

information.

VII. CONCLUSION

In this paper, I described the term context and context

awareness, its conceptual framework, listed the three

important context-aware applications that have been built

and major issues. Many of the context-aware systems lack

security options. Every system and framework uses its own

format to describe context and its own communication

mechanisms. But yet, its believed that context awareness is

the key factor for new applications in the area of pervasive

computing. I believe, however, that context awareness is a

key factor for new applications in the area of ubiquitous

computing.

VIII. REFERENCES

1. http://en.wikipedia.org/wiki/context-

aware_prevasive_systems.

2. A Survey on Context-Aware Systems: Matthias

Baldaf and Schahram Dustdar and Florian

Rosenberg.

3. A Software Engineering Framework for Context-

Aware Pervasive Computing: Karen Henricksenand Jadwiga Indulska.

4. Context-Aware Computing Applications: Bill N.

Schilit, Norman Adams, and Roy Want.

5. A Survey on Context-Aware Mobile Computing

Research: Guanling Chen and David Kotz.
http://en.wikipedia.org/wiki/context-aware_prevasive_systemshttp://en.wikipedia.org/wiki/context-aware_prevasive_systemshttp://en.wikipedia.org/wiki/context-aware_prevasive_systemshttp://en.wikipedia.org/wiki/context-aware_prevasive_systemshttp://en.wikipedia.org/wiki/context-aware_prevasive_systems


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