Abstract
The Worldwide Sensor Web has been applied for monitoring the physical world with spatial and temporal scales that were impossible in the past. With the development of sensor technologies and interoperable open standards, sensor webs generate tremendous volumes of priceless data, enabling scientists to observe previously unobservable phenomena. With its powerful monitoring capability, the sensor web is able to capture time-critical events and provide up-to-date information to support decision-making. In order to harvest the full potential of the sensor web, efficiently processing sensor web data and providing timely notifications are necessary. Therefore, we aim to design a software component applying the publish/subscribe communication model for the sensor web. However, as sensor web data are geospatial in nature, existing topological operators are inefficient when processing a large number of geometries. This paper presents the Aggregated Hierarchical Spatial Model (AHS model) to efficiently determine topological relationships between sensor data and predefined query objects. By using a predefined hierarchical spatial framework to index geometries, the AHS model can match new sensor data with all subscriptions in a single process to improve the query performance. Based on our evaluation results, the query latency of the AHS model increases 2.5 times more slowly than that of PostGIS. As a result, we believe that the AHS model is able to more efficiently process topological operators in a sensor web publish/subscribe system.
Highlights
In recent years, large-scale sensor arrays and the vast datasets produced worldwide have been utilized, shared, and published by a rising number of data providers
With open standards defining data schemas and web service interfaces, such as the Open Geospatial Consortium (OGC) Sensor Web Enablement (SWE) standards, sensors, and their data can be integrated in an interoperable manner, which has become the main idea behind the Worldwide Sensor Web [1,2,3]
We focus on the topological operators, which are used to determine the geospatial relationships defined in the OGC Simple Feature Access specification [16]
Summary
Large-scale sensor arrays and the vast datasets produced worldwide have been utilized, shared, and published by a rising number of data providers. Whenever the system receives new data, it executes the predefined queries and sends the results to users as notifications In this way, the publish/subscribe model can provide notifications more promptly than the request/response model. The aim of this paper is to propose a new approach to efficiently process topological operators in a sensor web publish/subscribe system. It presents the Aggregated Hierarchical Spatial Model (AHS model) for processing topological queries based on the nature of continuous query processing. As queries are predefined and continuous in a publish/subscribe system, the AHS model pre-generates the necessary indices for geometries of subscriptions and reuses them whenever new data arrive.
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