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|Title:||Query Processing In P2p Overlays(διαχείριση Ερωτημάτων Σε Δίκτυα Ομοτιμών)|
|Abstract:||We are interested in query processing problems that occur in peer-to-peer (hereafterP2P) overlays. We consider both structured and unstructured overlays thathandle structured or unstructured data. While structured frameworks provide reliableand efficient solutions, in many realistic scenarios the P2P topology cannot becontrolled and, thus, structured overlays are not applicable. Since P2P file sharingis so popular in successful commercial applications and P2P data management systemsare a new promising trend, we investigate competitive frameworks in objectmanagement.We study the heterogeneity and the data coordination problem that arise inunstructured overlays that consist of peer databases. We present GrouPeer, anadaptive, automated approach for the problem of sharing structured data in aP2P network in the absence of a standard mediated schema. By allowing peersto individually choose which rewritten version of a query to answer and evaluatethe received answers, information-rich sources left hidden otherwise are discovered.Gradually, the overlay is restructured as semantically similar peers are clusteredtogether. Extending the capabilities of GrouPeer, we propose a scheme that automatesthe process of creating schema synopses from semantic clusters of peers whichown autonomous relational databases. The resulting mediated schemas can be usedas global interfaces for relevant queries.For the data coordination problem in peer databases we describe distributedtriggers. We present an SQL3 compatible trigger language for the P2P setting. Wealso extend the SQL3 processing mechanism to this setting. Our trigger processingmechanism consists of an execution semantics, a set of termination protocols to dealwith peer transiency, and a set of protocols for managing peer acquaintances inpresence of distributed triggers.Moreover, we discuss problems that arise in unstructured fast evolving overlaysboth in content and connectivity. We investigate the issues related to the aboveproblem and propose a P2P andMobile Agent architecture based on Active Databasetechnology.Finally, we consider the problem of handling spatial data in distributed environments,focusing on applications of structured P2P overlays. We perform a generalstudy on the construction of a framework for autonomous sites that are boundto spatial information. We investigate the parameters of such a distributed environmentin order to perform search guided by locality and directionality in space.Furthermore, we present SpatialP2P, a totally decentralized indexing and routingtechnique that is suitable for P2P applications, in which spatial information of varioussizes can be dynamically inserted or deleted, and peers can join or leave. Theproposed technique preserves well locality and directionality of space.|
|Appears in Collections:||Διδακτορικές Διατριβές - Ph.D. Theses|
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