A Study of Context-Awareness: Gaia & SOCAM Presented by Dongjoo Lee IDS Lab., Seoul National University Gaia: A Middleware Infrastructure to Enable Active Spaces Manuel Roman, Christopher Hess, Renato Cerqueira, Anand Ranganathan, Roy H. Campbell, Klara Nahrstedt Department of Computer Science, University of Illinois at Urbana-Champaign, USA A Service-oriented Middleware for Building Context-aware Services Tao Gu a,b, Hung Keng Pung a, Da Qing Zhang b a Network Systems and Services Laboratory, Department of Computer Science, National University of Singapore, Singapore b Context-Aware System Department, Institute for Inforcomm Research, Singapore

Copyright  2008 by CEBT Contents  Gaia Introduction Architecture Services Application Framework  SOCAM Introduction Context Modeling and Reasoning Architecture Components Performance Evaluation  Comparison  Discussion 2

Copyright  2008 by CEBT Gaia: Introduction  Active Space an extension to physical space – Homes, offices, and meeting rooms capable of sensing user actions and equipped with a large variety of devices will assist users with different tasks. require a middleware infrastructure that supports the development and execution of user-centric mobile applications  Gaia a distributed middleware infrastructure that coordinates software entities and heterogeneous networked devices contained in a physical space encapsulates the heterogeneity of active spaces, and presents them as a programmable environment, instead of a collection of individual and disconnected heterogeneous devices Similar to traditional OS 3

Copyright  2008 by CEBT Physical and Active Space 4

Copyright  2008 by CEBT Gaia Architecture  Component Management Core dynamically loads, unloads, transfers, creates, and destroys all the components and applications of Gaia  Gaia components are distributed objects so that require communication middleware to support remote interaction uses CORBA to communicate with each other 5

Copyright  2008 by CEBT Services  Event service distributes events in the active space and implements a decoupled communication model based on suppliers, consumers, and channels.  Context service allows applications to query and register for particular context information so that they may adapt to their environment. consists of context providers that provide information about the current context.  Presence service detects digital and physical entities present in an active space. four basic types of entities: application, service, device, and person.  Space repository stores information about all software and hardware entities contained in the space (e.g., name, type, and owner) and provides functionality to browse and retrieve entities based on specific attributes.  Context file system incorporates context into the traditional file system model to provide support for mobile users, device heterogeneity, and data organization. /type:/papers/current: /location:/RM2401/situation:/meeting 6

Copyright  2008 by CEBT Application Framework  Distributed component-based infrastructure Model View Controller – model – presentation – controller – coordinator  Mapping mechanism customizes applications to different active spaces application description file – Application Generic Description (AGD) – Application Customized Description (ACD): generated by specialization mechanism using AGD  Policies customize different aspects of the applications define different sets of rules to customize several aspects of applications including instantiation, mobility, reliability, and composition (number of components and their bindings) 7

Copyright  2008 by CEBT Lua: Gaia’s Scripting Language  LuaOrb high level scripting language based on the Lua used to program and configure active spaces and to coordinate the active entities they contain simplifies management and configuration tasks allows for rapid prototyping and testing  Example: instantiate and assemble an MP3 application 8

Copyright  2008 by CEBT SOCAM: Introduction  Context any information that can be used to characterize the situation of an entity [Dey and Abowd, 2000]  A context-aware service is a network service which uses various contexts and adapts itself to the change of environment dynamically and automatically  Architectural Requirements A common context model that can be shared by all devices and services A set of services that perform context acquisition, context discovery, context interpretation and context dissemination 9

Copyright  2008 by CEBT Context Modeling and Reasoning  An ontology-based context modeling using OWL formal context model represented as first-order predicate calculus extendable to complex context or a set of contexts by combining the predicate and Boolean algebra  Two-layer hierarchical approach Common upper ontology Domain-specific ontologies  Context classification and dependency Direct Context – sensed context: acquired from physical sensors -> sensed – defined context: defined by a user -> defined Indirect Context -> deduced – derived by interpreting direct context through context reasoning – (Person,Location,Bathroom) ˄ (WaterHeater,Status,On) ˄ (Door,Status,Closed) => (Person,Status,Showering) different reliability 10

Copyright  2008 by CEBT Common Upper Ontology  defines basic concepts person, place, physical or computational object  14 classes, 6 properties 11

Copyright  2008 by CEBT Domain Specific Ontology  defines the details of general concepts and their properties  Example: IndoorSpace 12

Copyright  2008 by CEBT SOCAM Architecture  Context providers, Context interpreter, Context database, Context-aware services, and Service locating service 13

Copyright  2008 by CEBT Service Components  Context providers abstract useful contexts from heterogeneous sources—External or Internal. convert them to OWL representations so that contexts can be shared and reused by other service components.  Context interpreter provides logic reasoning services to process context information. Tasks – deriving high level contexts from low level contexts – give querying capability of context knowledge – maintaining the consistency of context knowledge – resolving context conflicts – provide deduced contexts Context Reasoner, Knowledge Base Reasoning – Ontology reasoning – User defined rule based reasoning: forward chaining, backward chaining, and hybrid execution model 14

Copyright  2008 by CEBT Service Components (cont’d)  Context database stores context ontologies and past contexts for a sub-domain.  Context-aware services agents, applications, and services make use of different level of contexts and adapt the way they behave according to the current context. pre-defined rules that specify actions triggered by a set of rules whenever the current context changes 15

Copyright  2008 by CEBT Service Components (cont’d)  Service locating service provides a mechanism where context providers and the context interpreter can advertise their presence and enables users or applications to locate these services. Implementation [Gu et al. (2003)]: features – scalability – dynamism – multiple matching capability  Communication and interaction between components Java RMI – interoperability between heterogeneous platforms – security 16

Copyright  2008 by CEBT Performance Evaluation  Implementation SOCAM Middleware: J2SE1.3.1 Context Interpreter: Jena2-HP’s Semantic Web Toolkit Ontology: OWL – Home domain: 89 classes, 156 properties – Vehicle domain: 32 classes, 57 properties Context provider: emulated in laptop  Performance Evaluation Logic reasoning is a bottleneck It is acceptable for running non-time-critical context-aware applications Overhead of the two-layer ontology design The reasoning performanceReasoning comparison Average time for concurrent requests 17

Copyright  2008 by CEBT Comparison GaiaSOCAM Architecture Middleware infrastructure (OS) Service oriented middleware Target Active space Semantic space Context Model No common context model Ontology based model (OWL) Deduced context Context Storing Context File System Knowledge Base, Context database App. Framework Partitioned App. based on MVC n/a Supporting Heterogeneity App. description file (AGD, ACD) Java Communication among Components CORBA JAVA RMI Service Triggering Depends on implementation of App. Pre-defined rule Security Future work partially with Java RMI Performance Evaluation n/a need to be improved acceptable for running non-time-critical context-aware applications 18

Copyright  2008 by CEBT Discussion  There are already many good architectures for enabling context aware services. Therefore we have to refer them profoundly.  SOCAM is much similar to our approach Service locating service Ontology based context model – reasoning  Needs more consideration about Personalization Security & Privacy Distributed control – cf) centralized control Synchronization of context information among devices 19