Handling spatial data in distributed environments

Handling spatial data in distributed environments is an intriguing issue. We consider autonomous sites of an overlay network that are bound to specific spatial information. We assume that each site has partial knowledge of the overlay. Actually, the sites are aware of and can communicate with some other sites, according to the spatial data to which they are bound to. We are interested in routing queries about spatial data in such overlays, solely by exploiting local knowledge on sites, i.e. based on locality and directionality in space. For such a system, we explore the parameters that can make search for any spatial information realizable and efficient. In this work we focus on the management of grid-partitioned space. In such a system there is a necessity for a mechanism that provides even knowledge of space to each site of the overlay. We investigate two different ways to define the directions of grid knowledge on each site and we propose a new distance metric. Moreover, we consider a new locality function that is specifically constructed in order to achieve even knowledge of space towards all directions. Furthermore, we present an experimental study that evaluates the theoretical propositions and verifies the theoretical results

Query processing in P2P overlays

We are interested in query processing problems that occur in peer-to-peer (hereafter P2P) overlays. We consider both structured and unstructured overlays that handle structured or unstructured data. While structured frameworks provide reliable and efficient solutions, in many realistic scenarios the P2P topology cannot be controlled and, thus, structured overlays are not applicable. Since P2P file sharing is so popular in successful commercial applications and P2P data management systems are a new promising trend, we investigate competitive frameworks in object management. We study the heterogeneity and the data coordination problem that arise in unstructured overlays that consist of peer databases. We present GrouPeer, an adaptive, automated approach for the problem of sharing structured data in a P2P network in the absence of a standard mediated schema. By allowing peers to individually choose which rewritten version of a query to answer and evaluate the received answers, information-rich sources left hidden otherwise are discovered. Gradually, the overlay is restructured as semantically similar peers are clustered together. Extending the capabilities of GrouPeer, we propose a scheme that automates the process of creating schema synopses from semantic clusters of peers which own autonomous relational databases. The resulting mediated schemas can be used as global interfaces for relevant queries. For the data coordination problem in peer databases we describe distributed triggers. We present an SQL3 compatible trigger language for the P2P setting. We also extend the SQL3 processing mechanism to this setting. Our trigger processing mechanism consists of an execution semantics, a set of termination protocols to deal with peer transiency, and a set of protocols for managing peer acquaintances in presence of distributed triggers. Moreover, we discuss problems that arise in unstructured fast evolving overlays both in content and connectivity. We investigate the issues related to the above problem and propose a P2P and Mobile Agent architecture based on Active Database technology. Finally, we consider the problem of handling spatial data in distributed environments, focusing on applications of structured P2P overlays. We perform a general study on the construction of a framework for autonomous sites that are bound to spatial information. We investigate the parameters of such a distributed environment in order to perform search guided by locality and directionality in space. Furthermore, we present SpatialP2P, a totally decentralized indexing and routing technique that is suitable for P2P applications, in which spatial information of various sizes can be dynamically inserted or deleted, and peers can join or leave. The proposed technique preserves well locality and directionality of space

A Standards-based Framework To Foster Geospatial Data And Process Interoperability

The quest for interoperability is one of the main driving forces behind international organizations such as OGC and W3C. In parallel, a trend in systems design and development is to break down GIS functionalities into modules that can be composed in an ad hoc manner. This component-driven approach increases flexibility and extensibility. For scientists whose research involves geospatial analysis, however, such initiatives mean more than interoperability and flexibility. These efforts are progressively shielding these users from having to deal with problems such as data representation formats, communication protocols or pre-processing algorithms. Once scientists are allowed to abstract from lower level concerns, they can shift their focus to the design and implementation of the computational models they are interested in. This paper analyzes how interoperability and componentization efforts have this underestimated impact on the design and development perspective. This discussion is illustrated by the description of the design and implementation of WebMAPS, a geospatial information system to support agricultural planning and monitoring. 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