Florin Dragan

Managing distributed workspaces with active XML

Publisher Summary This chapter discusses the distributed workspaces with active XML. The tremendous evolution of the Web has brought the need for platforms allowing to easily deploy distributed data management applications. The current trend goes towards the de-centralization of such platforms, and in particular to peer-to-peer architectures. The active XML system provides a peer-to-peer data integration platform, based on Web standards such as XML, and Web services. The system is centered on Active XML system (AXML) documents: XML documents where parts of the content are explicit XML data, whereas other parts are dynamically generated by calls to Web services on the same or on other peers. By including web service calls, AXML documents already have an inherent form of distributed computation.

P2P Semantic Mediation of Web Sources

XML Mediators are focused on supporting the XQuery (or sometimes the SQL/XML) query language on XML views of heterogeneous data sources. Wrappers leverage data sources to XML views with basic query capabilities. The data are integrated on demand by the mediator delegating sub-queries to wrappers. Using such information integration platforms to query the semantic web is a challenge both for scalability and data semantic reasons. On another side, semantic Peer-to-peer (P2P) networks are emerging as an important infrastructure to manage distributed data, notably on the web. An important goal concerns improving query facilities of distributed heterogeneous data. Coupling data mediation and P2P technology, P2P data mediation strives to support efficiently advanced queries upon heterogeneous data sources annotated with various metadata and mapping schemes. We analyze the main services provided by mediation systems and discuss their extension to the semantic web in P2P mode. We shortly discuss the annotation service for describing sources syntactically and semantically, the routing service to route data location requests, and the query service to resolve distributed queries. We survey some projects and report on PathFinder, an experimental P2P mediation system developed at University of Versailles in the Context of the Satine European project.

MediaPeer: A Safe, Scalable P2P Architecture for XML Query Processing

Increasing popularity of XML and P2P networks has generated much interest in distributed processing of XML data. We propose a novel solution organized around a mediator capable of processing XQueries over multiple heterogeneous data sources. The solution consists in a hierarchical overlay network formed of peers and super-peers indexing the XML path of data sources. Our solution is: (i) Scalable as the network can grow dynamically with size adaptative trie-based indexes in each super-peer. (ii) Reliable as procedures are developed for recovering from node failures or root saturations. (iii) Efficient as query processing is done by an existing optimized mediator that can track query process progresses and response sizes

A semantic layer for publishing and localizing xml data for a p2p xquery mediator

In this poster, we present the P2P XML data localization layer of XLive, an XQuery mediation system developed at University of Versailles [2]. A major challenge in the evaluation of XQuery over a P2P network in the context of multiple XML sources is to abstract from structural heterogeneity. Most existing approaches have mainly exploited varied types of 1:1 semantic mappings between peer schemas and/or ontologies. Complex query algorithms are required to exploit these semantic links between peers. In contrast, our approach focuses on a simple semantic layer. It is built on a Chord [4] DHT for indexing semantic descriptions of mediated data sources. A mapping process transforms an XML view of a mediator (each peer is equipped with a mediator) to a semantic form that is published into the P2P network and stored in the DHT. For a given user query, a search in the DHT retrieves all relevant data sources able to contribute to the result elaboration. Then, every peer that contains relevant data is directly queried to collect data for elaborating the final answer.

Interrogation de sources XML dans un réseau pair-à-pair par extension d'un médiateur XQuery

XML Mediators are focused on supporting the XQuery query language on XML views of heterogeneous data sources. The data are integrated on demand by the mediator delegating sub-queries to sources. On another side, Peer-to-peer (P2P) networks are emerging as an important infrastructure to manage distributed data, notably on the web. Coupling data mediation and P2P technology improves the facilities of data deployment and exchange in a large scale for business applications, because it requires no centralized administration and should be able to provide good performances. In this paper, we analyze the main services provided by mediation systems and P2P networks. Then, we describe our technical solutions and our XML P2P network based on an extension of the existing XLive centralized mediator.