1. An Ontology-based Approach to Context Modeling and Reasoning in Pervasive Computing
Dejene Ejigu, Marian Scuturici, Lionel Brunie Laboratoire INSA de Lyon, France
Fifth Annual IEEE International Conference Pervasive Computing and Communications Workshops (PerComW 07), 2007
Summarized and Presented by Seungseok Kang IDS Lab.

2. Outline Introduction Related Works Context Modeling
What is context?
Using reification in context modeling
The need for semantic context model
Ontology based context management model
Case study on reasoning
Conclusion and Future Work

3. Conceptual framework of pervasiveness
Introduction
The emergence of pervasive computing environment
Context and context-awareness are the key components in pervasive computing
Pervasive environment
Dynamicity
Heterogeneity
Ubiquity
Goals
Propose and investigate ontology based semantically rich, reusable and scalable context management model
Support collaborative reasoning in a multi-domain pervasive context-aware application
Conceptual framework of pervasiveness

4. Related Works CoolTown CoBra-ONT CONON CSCP
development of application specific context-aware systems
CoBra-ONT
Context model based on semantic web approach with context broker
CONON
Ontology for reasoning and representation
CSCP
Resource description framework for representation and manipulation of context data

5. Context Modeling What is Context?
Computational entities should be able to adapt themselves to changing situations
Dey et al.’s definition of context
The most widely referenced definition
“Any information that can be used to characterize the situation of an entity. An entity is a user, a place, or a physical or computational object that is considered relevant to the interaction between a user and an application, including the user and application themselves.“
Context Definition
Operation terms
Inherent characteristics of the entity
Interpretation of the operations involved on an entity

6. Context Modeling (cont.)
Hierarchy of context entities and relations
Primary characteristics of a context : Actor (subject)
Type and value of context is expressed by predicate and object
Ontology Representation
Basic RDF Triple <subject predicate object>
hierarchical classification of context
All descriptors have some properties to inherit from the root ContextEntity
Lower entities indicates context on the specific domain if application (instances)

7. RDF data model on context reification
Using Reification
Context modeling requires additional information
time, place, validity, claims, doubts, proofs, …
Extend the context model towards probabilistic models
RDF reification
Method to represent additional context attributes
Four properties used to model the original statement
Subject, predicate, object, type
Example
“Bob is located in the library” - “is reported by sensor #5” - “has accuracy of 88%” - “has occurred at 11:40 today”
RDF data model on context reification

8. The Need for Semantic Context Model
Example
Need for a context model that describe concepts, concept hierarchies, relationships between concepts
Using OWL to define properties, relations, and axioms
Enhance the potential of semantic context reasoning
“if user1 is located in a roomN and user2 is also located in roomN then conclude that they are coLocatedWith each other or according to the above similarity definition they are together” a
SELECT subject FROM table.context WHERE predicate=“isLocatedIn” AND object=“Room-305”
……Result?

9. Ontology Based Context Management Model
Generic Context Management (GCoM) Model
Context Ontology
semantics, concepts, relationships in the context data
Context Data
Instances of context
Context Related Rules
Derivation axioms that are used by systems to reason out and derive decisions about the actions that follow
explicit rules (by user) / implicit rules (by system itself)
General Components of the GCoM model

10. Ontology Based Context Management Model (cont.)
Example : cell phone ringing tone management service
Student must have their cell phones set to non disturbing modes (automatically) during different activities
Attending lecture
Consultation with their professors
In libraries
Student need to have their phones automatically switched to silent or vibrating mode when they are engaged in activities
It must be switched back when they are engaged in none of activities
Student like to use a decent ringing tone when in the vicinity of the campus
They also like to use musical ringing tone when outside the campus

11. Ontology Based Context Management Model (cont.)
Part of context ontology for the scenario (OWL)
Context representation for the scenario (RDF/XML) (Can be stored in any standard database format)

12. Ontology Based Context Management Model (cont.)
Domain specific rules (using Jena)
For student’s explicit wishes in the scenario
Rule representation for the scenario

13. Case Study on Reasoning
Context-aware service platform with GCoM model
Interface Manager
Manages a user interface and other modules
GCoM model
Provide the data necessary to provide proactive or reactive context-aware service
Rules
Plays an important role in the process of reasoning about context
Implicit rules (derived from the ontology)
Explicit rules (defined by user in the specific domain)
GCoM in a context-aware platform

14. Case Study on Reasoning (cont.)
Context-aware Service
Provide the core context-aware services
Reasoning, decision making, action selecting
Supplementary Service
Types of service which use the information from context-aware service
Knowledge Discovery, Collaboration, Security, …
Revise: campus cell phone ringing tone management
Three GCoM element
OWL for context ontology (cellphone.owl)
RDF/XML for context data representation (cellphone.ctxt)
RDQL/SparQL for rule management and reasoning (cellphone.rules)

15. Conclusion
Propose the GCoM model based on ontology representation of context data, its semantics, context instances and rules
Rules are either derived or defined by user based on the requirement and policies
Breaking down of context in to semi-independent components is a unique contribution of GCoM
Context Instance, Context Semantics, Context Rules
GCoM make the context dynamic and reusable in a pervasive computing environment
Future work
Incorporate and use GCoM model with CoCA service platform
Evaluate the performance of proposed model and platform
Guarantee Scalability by separating relevant context data