Context-Awareness on Mobile Devices – the Hydrogen Approach
Sangkeun Lee
Context-Awareness for Mobile
Devices
• Support context-awareness for considering
– Special requirements of mobile devices regarding the
limitations of network connections, computing power
• Requirements for an architecture of a framework to
support context-awareness on mobile devices
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Lightweightness
Extensibility
Robustness
Meta-Information
Context-Sharing
• Separiting the concerns of context sensing from the
application is needed
Hydrogen Context-Framework
• Three architecture
– Application Layer
– Management Layer : Context Server
• Provide simple methods for the applications for
retrieving or subsribing to a context
– Adaptor Layer
• Responsible to get information from sensors
– Reusability, Exchangeability of sensors &
adoptors
Implementation – the Hydrogen
Approach
• Prototype Implementation
– PersonalJava virtual machines Jeode, J2ME, iPAQs, PocketPC 2002
• Context
– Time, Location, Device, User, Network
• ContextClient
– Responsible for communication : open ports, queries data
• Context Server
– Java Executable object
– Communication in two forms : XML-streams, serialized Java objects
• Extensibility
– toXML(), fromXML()
• Open Issues
– Comprehensive Context Model
– XML Protocols
– Context Sharing
CASS- Middleware for Mobile Context-Aware Applications
Sangkeun Lee
General
• CASS (Context-awareness sub-structure)
– Server based extensibile middleware to
support context-aware applications on
mobile devices
• High-level context data abstraction
• Separation of context based inferences from
application code
• Configurable by users
CASS Overview
• Requirements
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Support many of context sources
Provision for context history
Support for context interpretation
Support higher-level abstraction of contexts
Should be event-based, extensible framework
Transparent use of distributed sources of context
Separation of application procedure
• Architecture
– CASS Applications do not need to store low-level details of context
sources and communicate with individual source
– CASS Middleware does that
• Design
– SensorListener listens for updates and stores context information
– ContextRetriever retrieves stored context
– ChangeListener allows a mobile computer to listen for context events
Data Management & Inference
• CASS uses a database for persistent data
store
– The database is server-based that does not
suffer from the storage space and performance
– Data can be read and manipulated using SQL
– Not only context, domain knowledge and rules
can be stored too
• Inference Engine
– Forward Chaining