Lecture07 Context Awareness and Mobile Middleware
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讲 情景感知与移动中间件
§ 7.1 Concept and Applications
§ 7.2 Context Sensing, Modeling and Reasoning
§ 7.3 Mobile Middleware


Create applications that work seamlessly in human environments
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Understanding of context
How do we effectively infer characteristics of situations and usefully supplement them with technology?

Entity
Museum Patron
(user)
Exhibit
Mobile Interface
Characteristic Info (context)
Education, age, language, location, artifacts viewed
What area of museum battery life

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By example
Location, time, identities of nearby users …
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By synonym
Situation, environment, circumstance
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By dictionary [WordNet]
The set of facts or circumstances that surround a situation or event

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Computing context: network connectivity, communication cost, communication bandwidth, nearby resource
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User context: user profile, location, social situation
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Physical context: lighting, noise, traffic condition, temperature
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Time Context: time of a day, week, month, season of a year

“Context is any information that can be used to characterize the situation of an entity. An entity is a person, place, or object that is considered relevant to the interaction between a user and an application, including the user and the application themselves.”
[Dey and Abowd, 2000]
Observations
From point of view of developer

 “A system is context-aware if it uses context to provide relevant information and/or services to the user, where relevancy depends on the user’s task.”

Active vs. Passive
Active Context Awareness:
“an application automatically adapts to discovered context by changing the application’s 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”

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Proximate selection: user interface where nearby objects are emphasized/made easier to choose
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Automatic contextual reconfiguration: a process of adding/removing components or changing relationships between components based on context change
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Contextual information and commands: produce different results according to the context in which they are issued
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Context-triggered actions: rules to specify how the system should adapt

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Extend browsers to refer to dynamic contextual information
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Dynamic URLs with contextual/environment variables
Variables get bound to current context when the URL is referenced
 Also support active documents
As the context changes, the document is automatically updated
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What types of context can be useful here?
Active or passive?
9

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Scenario: you are at home depot trying to figure out what you need to finish your basement
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Shopping assistant can
Tell you what parts you need
Where to find them relative to your location in the store
What is on sale
Do comparative pricing
Use your previous profile information to customize shopping and delivery

What context? Active/passive?
10

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Characteristic
From Georgia Tech
Provide information services to a tourist
Direction
Background information
Travel diary (automatically recorded)
Indoor and Outdoor Version
Indoor
Using IR (infrared)
Outdoor
Using GPS
Figure : Outdoor
Cyberguide
Screenshot, etc.
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How to get context information?
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How to model and represent the information collected?
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How to obtain high level information from raw/low level information?

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Outdoor
GPS
Alternatives?
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Indoor ?
Need to build our own location tracking system difficult problem
Use ideas similar to GPS: compute distances from known locations that send beacons

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Time?
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Physical sensors possible
Light, acceleration, tilt, sound, temperature, pressure, proximity of humans
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Nearby objects?
If system keeps track of location of objects, query to a database
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Bandwidth?
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Orientation?
Orientation sensor based on two mercury switches
Directional antennas/directional transmitters?
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Context Modeling
To define and evaluate context information
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Context Reasoning, to derive new context facts from existing context facts and/or reason about high-level context abstractions that model real world situations.

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Early approaches
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Key-value models
List of attributes and their values
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Markup models
Use a variety of markup languages including XML

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To model context for specific domains
E.g. context-aware browsing
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Using tuples to represent context
Who, What, Where, When
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With interface to store and query such tuples

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Context Modeling Language (CML)
Developed for modeling of databases
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It can capture the different classes and sources of context specifically, static, sensed, derived, and user-supplied
(''profiled'') information; capture imperfect information using quality metadata and the concept of ''alternatives'' for capturing conflicting assertions (such as conflicting location reports from multiple sensors; capture dependencies between context fact types; and capture histories for certain fact types and constraints on those histories.

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'' Fitzwilliam Darcy located at Kitchen''

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Space is an (maybe the most) important context
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Predefined (static) vs. obtained from positioning sys.
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Two kinds of coordinate sys.
Geometric coordinates
E.g. latitude, longitude, and elevation above sea level
Support range query, distance query
Symbolic coordinates
Represented by an identifier, e.g. a room number
No spatial relation offered
Explicit relation information should be provided additionally to support range/distance query

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Context is a kind of knowledge
Can be represented and handled by knowledge framework
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Ontology: 本体，物体的本质、抽象
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OWL （ Web Ontology Language ）
W3C 开发的一种网络本体语言，用于对本体进行语
义描述。
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Context modeling using OWL classes, individuals, characteristics of individuals (data type properties), and relations between individuals
(object properties)

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For example, given two atomic classes Person and
Female, the class Male can be defined as:
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For example, BusinessMeeting can be defined as:

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Low-level context
Information from physical sensors
Meaningless, trivial, vulnerable to changes, uncertian
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High-level context: situational context, situation

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Hybrid models
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Uncertainty

Security

Privacy

 What’s Middleware?
Widely used and popular term
“A set of service elements above the operating system and the communications stack”
“Software that provides a programming model above the basic building blocks of processes and message passing”

 Application development is complex and time-consuming
Should every developer code their own protocols for directories, transactions, ..?
How to cope with heterogeneous environments?
Networks, operating systems, hardware, programming languages
 „
To cut down development time
Rapid application development
Simplify the development of applications
Support heterogeneous environments and mask differences in OS/languages/hardware

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Transactional Middleware
Offers a tuple abstraction (SQL)
Distributed transaction processing (DTP protocol)
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Message-Oriented Middleware (MOM)
Offers a mailbox abstraction
Asynchronous messages
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Procedural (RPC)
Offers a procedure abstraction
Synchronous client/server interaction
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Object and Component-oriented Middleware
Offers an object abstraction
(A)synchronous client/server interaction
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Event Based Middleware
Trading, brokering

Device Control


Distributed transparency

Scalability
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Openness
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Heterogeneity
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Reliability
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Resource sharing

Security

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Necessity
Diversity of mobile device
Diversity of mobile OS
Diversity of communication standards
Constraints of mobile resources
Diversity/Dependency on environments/contexts
 Additional requirement
Light weight
Asynchrony
Self-adaptation
Visibility (to some extent)
Coordination support
Component support


Service discovery
To find the service required with respect to mobility, context
Service advertising + service discovering
SLP, UPnP, Jini, etc.
 Disconnection support
Replication and cache
 Context awareness
Sensing and reasoning

Self-adaptation
Adapting behavior/configuration of app.
Based on context changes
At different levels


Agents can be defined to be autonomous, problemsolving computational entities capable of effective operation in dynamic and open environments
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Additional characteristics
Reactivity for reacting to the change of environment
Veracity for prohibiting wrong information

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Agent-based management of context information
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Context-awareness via learning, inferencing and cooperation
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Providing context information
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Support autonomous service via complex sensing information


SOMA
Mobile agent based
Using Java
Mobility support: user mobility, device mobility
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CARISMA
For context-awareness
Based on reflection technique

PDAgent
Agent based
To execute tasks on behalf of users

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Concepts
Context
Context model
Middleware

Different context models
Key-value and Markup
Domain specific
Object-role based: CML
Spatial
Ontology based

Mobile middleware
Purpose
Requirement

1. Self-adaptation to context changes can be realized in different levels, in terms of system architecture. Please tell and discuss such levels.
2. Can context-awareness be done at a set of nodes cooperatively? What’s the key issue then, compared with that at a single node?