Lecture07 Context Awareness and Mobile Middleware
第7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
Why Context Aware?
 Create applications that work seamlessly in human
 Understanding of context
How do we effectively infer characteristics of situations
and usefully supplement them with technology?
Museum Audio Guide Example
Museum Patron
Characteristic Info (context)
Education, age, language,
location, artifacts viewed
Mobile Interface
What area of museum
battery life
What is Context?
 By example
Location, time, identities of nearby users …
 By synonym
Situation, environment, circumstance
 By dictionary [WordNet]
The set of facts or circumstances that surround a
situation or event
Context Definition
 Computing context:
network connectivity, communication cost,
communication bandwidth, nearby resource
 User context:
user profile, location, social situation
 Physical context:
lighting, noise, traffic condition, temperature
 Time Context:
time of a day, week, month, season of a year
Operational Definition of Context
“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]
- From point of view of developer
Context-Aware Applications
 “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”
CA Applications
 Proximate selection:
user interface where nearby objects are
emphasized/made easier to choose
 Automatic contextual reconfiguration:
a process of adding/removing components or changing
relationships between components based on context
 Contextual information and commands:
produce different results according to the context in
which they are issued
 Context-triggered actions:
rules to specify how the system should adapt
Mobisaic Web Browser
 Extend browsers to refer to dynamic contextual
 Dynamic URLs with contextual/environment variables
Variables get bound to current context when the URL is
 Also support active documents
As the context changes, the document is automatically
 What types of context can be useful here?
Active or passive?
Shopping Assistant
 Scenario: you are at home depot trying to figure out what
you need to finish your basement
 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?
From Georgia Tech
Provide information services to a
Background information
Travel diary (automatically
Indoor and Outdoor Version
Using IR (infrared)
Using GPS
Figure : Outdoor
Screenshot, etc.
§7.2 Context Sensing, Modeling and Reasoning
 How to get context information?
 How to model and represent the information collected?
 How to obtain high level information from raw/low
level information?
Sensing Location Information
 Outdoor
 Indoor ?
Need to build our own location tracking system
difficult problem
Use ideas similar to GPS: compute distances from known
locations that send beacons
Sensing Other Contexts
 Time?
 Physical sensors possible
Light, acceleration, tilt, sound, temperature, pressure,
proximity of humans
 Nearby objects?
If system keeps track of location of objects, query to a
 Bandwidth?
 Orientation?
Orientation sensor based on two mercury switches
Directional antennas/directional transmitters?
Context Modeling and Reasoning
 Context Modeling
To define and evaluate context information
 Context Reasoning, to
derive new context facts from existing context facts
reason about high-level context abstractions that model
real world situations.
Key-value and Markup Modeling
 Early approaches
 Key-value models
List of attributes and their values
 Markup models
Use a variety of markup languages including XML
Domain-focused Modeling
 To model context for specific domains
E.g. context-aware browsing
 Using tuples to represent context
Who, What, Where, When
 With interface to store and query such tuples
Object-role based Modeling and Reasoning
 Context Modeling Language (CML)
Developed for modeling of databases
 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.
An Example CML Model
Query using a Three-valued Logic
 '' Fitzwilliam Darcy located at Kitchen''
Spatial Modeling and Reasoning
 Space is an (maybe the most) important context
 Predefined (static) vs. obtained from positioning sys.
 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
Ontology-based Modeling and Reasoning
 Context is a kind of knowledge
Can be represented and handled by knowledge
 Ontology: 本体,物体的本质、抽象
 OWL(Web Ontology Language)
 Context modeling using OWL
classes, individuals, characteristics of individuals (data
type properties), and relations between individuals
(object properties)
Ontology-based Modeling and Reasoning
 For example, given two atomic classes Person and
Female, the class Male can be defined as:
 For example, BusinessMeeting can be defined as:
High-level Context Abstractions
 Low-level context
Information from physical sensors
Meaningless, trivial, vulnerable to changes, uncertian
 High-level context: situational context, situation
Other Issues
Hybrid models
§7.3 Mobile Middleware
 What’s Middleware?
Widely used and popular term
„Fuzzy term
„One definition
“A set of service elements above the operating system
and the communications stack”
„Second definition
“Software that provides a programming model above the
basic building blocks of processes and message passing”
What’s Middleware
Why Middleware
 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
 „Middleware is needed
To cut down development time
Rapid application development
Simplify the development of applications
Support heterogeneous environments and mask differences
in OS/languages/hardware
Middleware Categories
 Transactional Middleware
Offers a tuple abstraction (SQL)
Distributed transaction processing (DTP protocol)
 Message-Oriented Middleware (MOM)
Offers a mailbox abstraction
Asynchronous messages
 Procedural (RPC)
Offers a procedure abstraction
Synchronous client/server interaction
 Object and Component-oriented Middleware
Offers an object abstraction
(A)synchronous client/server interaction
Event Based Middleware
Trading, brokering
 Device Control
Requirements for Middleware
Distributed transparency
Resource sharing
Mobile Middleware
 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
Visibility (to some extent)
Coordination support
Component support
Key Technologies in Mobile Middleware
 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
Context-awareness and Self-adaptation
Mobile Agent based Middleware
 Agents can be defined to be autonomous, problemsolving computational entities capable of effective
operation in dynamic and open environments
 Additional characteristics
Reactivity for reacting to the change of environment
Veracity for prohibiting wrong information
Mobile Agent Platform
Agents for context-awareness
 Agent-based management of context information
 Context-awareness via learning, inferencing and
 Providing context information
 Support autonomous service via complex sensing
Case Studies
Mobile agent based
Using Java
Mobility support: user mobility, device mobility
For context-awareness
Based on reflection technique
 PDAgent
Agent based
To execute tasks on behalf of users
A Summary
 Concepts
Context model
 Different context models
Key-value and Markup
Domain specific
Object-role based: CML
Ontology based
 Mobile middleware
Homework Questions
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?
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