Context-Awareness on Mobile Devices – the Hydrogen Ap-proach

Sangkeun Lee

Context-Awareness for Mobile De-vices

• 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– 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-struc-ture)– 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

– 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 & Infer-ence

• CASS uses a database for persistent data store– The database is server-based that does not

suffer from the storage space and perfor-mance

– Data can be read and manipulated using SQL– Not only context, domain knowledge and

rules can be stored too

• Inference Engine– Forward Chaining