May 06 Using Moving Object Databases to Provide Context Information in Mobile Environments Katharina Hahn 1 A. Voisard 1,2, M. Scholz 1, H. Schweppe 1, J. Böse 1 1 Databases and Information Systems, FU Berlin 2 Fraunhofer Institute for Software and Systems Engineering (ISST), Berlin

Katharina Hahn 2 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Support Mobile Transactions

Katharina Hahn 3 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Overview  Motivation  Background  Related Work  Context System  Modeling Context  Storing Context  Querying Context  Exchanging Context  Conclusion  Future Work

Katharina Hahn 4 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Motivation  Support transactions in MANETs [1]  eLearning scenario  Change of electronic goods  Distributed commit  Support atomic commit  Replicate recovery information for failing nodes  Recovering nodes will follow global decision  Provide recovery probability  How to disseminate recovery information to reach high availability?  Disseminate among preferably stable nodes  Avoid flooding the MANET  Determine „stable“ nodes within surrounding

Katharina Hahn 5 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Background  System model  Heterogeneous MANET  Nodes differ according to  Mobility (stable vs. mobile)  Resources (highly vs. poorly equipped)  Context awareness  Gather knowledge of currently surrounding nodes  Enable prediction of behavior of nodes  Consider probability of failure of nodes

Katharina Hahn 6 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Related Work  What is considered to be context?  Schilit (1994)  Three important aspects of context are: where your are, who you are with and what resources are nearby [2].  Dey (1999)  Context is any information that can be used to characterize the situation of an entity [3].  Too general  Mobile peer-to-peer environment with limited resources forces to focus on certain context attributes

Katharina Hahn 7 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06  Context aware systems  Numerous approaches exist  e.g. SOCAM [4], PACE [5]  Predicting Context  Not only deals with recognizing and reasoning on current context  Focuses on prediction of context [6]  Sensing  Feature Extraction  Classification  Labeling  Prediction Related Work (2)

Katharina Hahn 8 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Overview  Motivation  Introduction  Related Work  Context System  Modeling Context  Storing Context  Querying Context  Exchanging Context  Conclusion  Future Work

Katharina Hahn 9 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Context Information  Objectives  MANET system: no central context server  Light-weight to be run on mobile devices  Establish local view on MANET (distributed context)  Enable prediction of future behavior of nodes  For application use  Evaluate nodes and their surrounding according to their stability  Will they be reachable for the duration of the transaction?  Will they be reachable by any recovering node so that they can learn about missed steps?

Katharina Hahn 10 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Context Model  Consider information which indicates  Connection status  Position, movement  Link stability, signal quality, transmission range  Battery power  No (external) environmental sensors considered  Do not focus on modeling user-initiated shut- down probability

Katharina Hahn 11 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Modeling Context Data  Explore different levels of context atomic attribute {attribute, value} e.g. position derived attribute {attributes}  attribute e.g. speed local context LC Source ID {attributes} auxiliary context Owner ID {{Source ID}, attribute} e.g. distance group context GC Owner ID {Source ID, context} group level local level

Katharina Hahn 12 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Storing Context Data  Every nodes, able to sense its context, can originate and send local context data  Nodes interested in their surrounding carry local DB  Relational DB with MOD concepts to model dynamic environment  Dynamic vs. static attributes node_idN103 rbt.updatetimet3 rbt.value00:53:00 rbt.function(t)-(0,0,1)*t rbt.uncertainty(0,10,0)  Dynamic attributes analogous to MOST data model [6]  Enables extrapolation (prediction)  Reduces network load opposed to conventional relational DB  Uncertainty serves as “contract”  Prediction of behavior is administered within local DB

Katharina Hahn 13 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Querying Context  Queries are submitted locally  Conventional querying using SQL  Temporal queries  e.g. querying inter/extrapolated states of dynamic attributes  Given set of temporal queries implemented  e.g. “When will distance be greater than transmission range?” region of interest node uncertainty  Must/may semantic  Strong indicator for probability that nodes stay connected  Use degree of overlapping future whereabouts with uncertainty and transmission range as foundation for probability evaluation

Katharina Hahn 14 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06  Motivation  Introduction  Related Work  Context System  Modeling Context  Storing Context  Querying Context  Exchanging Context  Conclusion  Future Work

Katharina Hahn 15 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Exchanging Context  Before beginning of interaction  Exchange information within certain number of hops  Classify involved nodes  Initiators gather GC  Sources sense LC  Inactive nodes

Katharina Hahn 16 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06  Event-triggered  Explicit update if conventional attribute changes  Dynamic attributes  A.uncertainty serves as contract  An update will be sent, whenever the current deviation exceeds the uncertainty |s ensed(dynAttr) – calculated(dynAttr) | > dynAttr. uncertainty  Adapt uncertainty to nodes behavior, e.g.  Sensible value if movement is fast  Robust value if remaining battery power is low Exchanging Context (2)

Katharina Hahn 17 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06  Time-based  Update all attributes periodically, if no update through event occurred  Learn about leaving and newly arrived nodes  Data in DB ages if no update of the node is received Exchanging Context (3)

Katharina Hahn 18 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06  Evaluation of gathered information using existing approaches [8,9]  Consider combination of energy resources, link stability and movement  Combine through  Weighted metric  Fuzzy logic  Consider failure probability Context Evaluation gather context evaluate node evaluate context

Katharina Hahn 19 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Platform  Implementation  J2ME CDC  OSGi  JAVA database  Platforms  Microsoft Windows Mobile  Navilock NL-216CX Compact Flash Sensors Context Exchange MOD wrapper Context evaluation DB

Katharina Hahn 20 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06  Motivation  Introduction  Related Work  Context System  Modeling Context  Storing Context  Querying Context  Exchanging Context  Conclusion  Future Work

Katharina Hahn 21 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Conclusion  Objectives were  MANET context model  Stability evaluation  Light-weight system  Multi-level context model  Storing, querying and exchanging context  Administrate context prediction within DB  Part of the CoCoDa middleware that supports mobile transactions

Katharina Hahn 22 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Future Work  Establish different prediction schemes on top of context system  Evaluation of system within middleware  Additional storage and network cost  Performance through evaluation of reliable recovery log provider  Does rate of successful recovery increase opposed to choosing nodes randomly at acceptable costs?

Katharina Hahn 23 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 Thank you for your attention!

Katharina Hahn 24 Managing Context Information and Semantics in Mobile Environments (MCISME) May 06 References [1] [2] Schilit et al.: Context-aware Computing Applications, 1st International Conference on Mobile Computing Systems and Applications, [3] Dey, Abowd: Providing Architectural Support for Building Context-Aware Applications, PhD Thesis, College of Computing, Georgia Institute of Technology, [4] Gu et. al: A Middleware for Building Context-Aware Mobile Services, n Proceedings of IEEE Vehicular Technology Conference, [5] Henricksen, Induslka et al.: Middleware for Distributed Context-Aware Systems, In OTM Conferences, [6] Mayrhofer: An Architecture for Context Prediction, Advances in Pervasive Computing, Part of 2nd International Conference on Pervasive Computing, [7] Sistla et. al: Modeling and Querying Moving Objects. 13th International Conference on Data Engineering, [8] Su, Lee, Gerla: Mobility Prediction In Wireless Networks, International Journal of Network Management, [9] Gruenwald and Banik: Power Aware Management Of Mobile Real-Time Database Transactions in ad-hoc Networks.