Msc. Thesis -Active Web Alert Service for Rule Based Alerting
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Active Web Alert Service for Rule Based Alerting in Sensor Web An Event Based Approach Anish Joshi March, 2005 Active Web Alert Service for Rule Based Alerting in Sensor Web An Event Based Approach by Anish Joshi Thesis submitted to the International Institute for Geo-information Science and Earth Observation in partial fulfilment of the requirements for the degree in Master of Science in Geoinformatics. Degree Assessment Board Thesis advisor Dr. Andreas Wytzisk Drs. Barend J. Kobben¨ Thesis examiners Chairman: Prof. Dr. Menno Jan Kraak External examiner: Ingo Simonis Supervisor: Dr. Andreas Wytzisk Second supervisor: Drs. Barend J. Kobben¨ INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION ENSCHEDE, THE NETHERLANDS Disclaimer This document describes work undertaken as part of a programme of study at the International Institute for Geo-information Science and Earth Observation (ITC). All views and opinions expressed therein remain the sole responsibility of the author, and do not necessarily represent those of the institute. Abstract The recent developments in sensor, computing, communication and soft- ware technologies have brought about a new concept: the Sensor Web.A Sensor Web is a macro-instrument consisting of a heterogeneous, intelli- gent, spatially distributed sensors deployed to monitor and explore the envi- ronment. Open Geospatial Consortium’s (OGC) Sensor Web Enablement (SWE) initiative provides an infrastructural framework to integrate au- tonomous sensor webs into Spatial Data Infrastructure (SDI). The integra- tion of sensor web-based real/near real time information into SDI would culminate in a new level of spatio-temporal decision support for critical application scenarios for climate, natural resources, environment, disas- ter management, critical infrastructure protection, homeland security and emergency response issues. This new level of decision support is achieved by the formalized knowledge of the facts and circumstances of the environment. However, there lacks a system in current SWE architecture that incorporates the rule based facts of the real world scenarios. This research work is an effort to conceptual- ize and develop an alerting geo-service that is capable of incorporating real world environmental, spatial and temporal rules that will help to get an in-depth insight of the real world phenomena for better decision making. Based on the use case scenario of flood early warning, a service is envisioned and designed that allows definition of spatio-temporal and observational rules pertaining to a flood event. The service communicates with underlying Sensor Collection Services (SCS) for sensor observation data and validates the data against predefined threshold rules. The service dispatches alert notifications to the subscribers based on the fulfillment of these threshold rules. Such an alerting service is realized through an Active Web Alert Ser- vice (AWAS). The AWAS extends current SWE components by incorporating a new service for alert notification as envisioned by Open Web Service 2 (OWS 2). The AWAS is built on top of event based communication model, a new com- munication paradigm for distributed GI-Services. The event based commu- nication model enables proactive communication pattern between the AWAS and SCS(s), enabling active dispatch of sensor observation data when the rules are satisfied. The event based model enables anonymous and asyn- chronous communication between SCS(s) and the AWAS. SCS(s) publishes its observations as events to the event service and the AWAS subscribes to the events defined by rules with the event service. A notification is sent to the subscriber AWAS when the published and subscribed events are matched. i Abstract This research work is an effort to conceptualize and design AWAS based on event based communication model as well as to investigate on enhance- ments required on current SWE components to support incorporation of the AWAS in SWE framework. Keywords Sensor Web, Rule Based Alerting, Active Web Alert Service, Event Based Communication, Emergency Warning ii Contents Abstract i List of Figures vii List of Tables ix Acknowledgements xi 1 Introduction 1 1.1 Background .............................. 1 1.2 Research Scenario ........................... 3 1.3 Problem Statement .......................... 3 1.4 Research Objective .......................... 4 1.5 Research Question .......................... 4 1.6 Research Scope ............................ 5 1.7 Thesis Structure ............................ 5 2 Interoperability Framework for Sensor Web 7 2.1 Integrating Sensor Web into SDI .................. 7 2.2 Interoperability Framework ..................... 8 2.2.1 Service Oriented Architecture ................ 9 2.2.2 Web Service .......................... 10 2.2.3 Open Geospatial Consortium ................ 11 2.2.4 OGC Specification ....................... 12 2.3 OGC Web Service Architecture ................... 16 2.3.1 OWS Framework ....................... 16 2.4 Sensor Web Enablement ....................... 18 2.4.1 SensorML ........................... 18 2.4.2 Observations & Measurements ............... 20 2.4.3 Sensor Collection Service .................. 25 2.4.4 Sensor Planning Service ................... 27 2.4.5 Web Notification Service ................... 29 2.5 Synopsis ................................ 31 3 Sensor Web for Spatio-Temporal Decision Support 33 3.1 Sensor Web in Emergency Management .............. 34 3.2 Use Case Scenario–Flood Management & Early Warning .... 35 iii Contents 3.2.1 Role of Sensor Web ...................... 37 3.3 Rule Based Alerting Service for Sensor Web ............ 37 3.3.1 General Concept ........................ 39 3.4 Requirements ............................. 40 3.4.1 Rule Registration ....................... 40 3.4.2 Communication Model .................... 42 3.4.3 Encodings of Alert Messages ................ 43 3.4.4 Extension of SWE components ............... 46 3.5 Open Issues .............................. 47 3.6 Synopsis ................................ 48 4 Event Based Communication Model 51 4.1 Event Based Communication .................... 51 4.1.1 Participants of Event Based Communication ....... 51 4.1.2 Characteristics of Event Based Communication ..... 51 4.1.3 Event .............................. 53 4.1.4 Event Notification ....................... 54 4.1.5 Filter .............................. 54 4.1.6 Pattern ............................. 55 4.1.7 Event Service ......................... 56 4.1.8 Advertise/Publish/Subscribe ................. 57 4.1.9 Event Notification Schemes ................. 57 4.1.10 Interaction Pattern ...................... 58 4.2 Synthesis: AWAS and Event Based Communication Model ... 60 4.2.1 AWAS Object Model ...................... 60 4.2.2 AWAS Event Model ...................... 60 4.2.3 Event Generation Schemes ................. 61 4.3 Open Issues .............................. 63 4.4 Synopsis ................................ 64 5 Active Web Alert Service - Architecture 65 5.1 Architectural Concept ......................... 65 5.1.1 Layered View ......................... 65 5.1.2 Structural View ........................ 66 5.1.3 Interface Operations ..................... 68 5.1.4 Behavioral View ........................ 71 5.2 Functional Design Components ................... 73 5.2.1 Event .............................. 73 5.2.2 Event Filter/Pattern ..................... 75 5.2.3 Event Publish/Subscribe ................... 75 5.2.4 Event Notification ....................... 75 5.2.5 Event Handling and Parsing ................ 76 5.3 Non-Functional Design Components ................ 76 5.3.1 Quality of Service ....................... 76 5.3.2 Temporal Synchronization of Events ............ 77 5.4 Deployment Concept ......................... 77 5.4.1 Process View .......................... 77 iv Contents 5.4.2 Deployment View ....................... 79 5.5 Open Issues .............................. 80 5.6 Synopsis ................................ 81 6 Proof of Concept 83 6.1 Implementation Framework ..................... 83 6.2 Implementation Technology ..................... 84 6.2.1 Java ............................... 84 6.2.2 Servlet ............................. 85 6.2.3 JDBC .............................. 85 6.2.4 XForm ............................. 85 6.2.5 XML Parser .......................... 86 6.3 Prototype ................................ 86 6.3.1 Siena Event Service ...................... 86 6.3.2 Implementation ........................ 88 6.3.3 Result .............................. 90 6.4 Synopsis ................................ 91 7 Conclusion and Recommendation 93 7.1 Conclusion ............................... 93 7.2 Recommendation for Future Work ................. 98 A 101 A.1 User rules expressed in Filter Encodings ............. 101 A.2 Common Alerting Protocol(CAP)Document Object Model .... 102 A.3 Example of user form for rule registration ............. 103 B 105 B.1 Results of prototype .......................... 105 B.1.1 Event Publishing ....................... 105 B.1.2 Event Subscription ...................... 106 Bibliography 107 Glossary 117 v Contents vi List of Figures 2.1 Publish-Find-Bind Pattern [11] ................... 10 2.2 Web Service interoperability stack ................. 11 2.3 UML Class diagram of OpenGIS Geodata Model adopted from [6] 14 2.4 UML Class diagram of Abstract and Implementation Service Spec- ifications adopted from Percivall [53] ................ 15 2.5 The OWS Service Framework [11] ................. 17 2.6