1 ISWC GridVine: Building Internet-Scale Semantic Overlay Networks Karl Aberer, Philippe Cudré-Mauroux, Manfred Hauswirth School of Computer and Communication Sciences (I&C) Swiss Federal Institute of Technology (EPFL) Tim van Pelt Department of Computer and Information Science Linköpings Universitet, Sweden NCCR-MICSKnowledgeWeb

2 Overview 1.Motivations Sharing resources in decentralized settings 2.The physical P2P layer: P-Grid 3.The logical semantic layer: GridVine Mapping annotations onto P-Grid Fostering semantic interoperability 4.Demo 5.Conclusions

3 1. Motivations Schema-based searches in P2P networks –Fixed set of schemas Ok for searching mp3s, trailers…

4 Peer Data Production Local documents –E.g., poster for Swiss NCCR-MICS project  Local schema creation –Retrieval performance (e.g., recall) w.r.t. global resources –Semantic interoperability? Title: Semantic Integration in Decentralized Settings Authors: Philippe Cudre-Mauroux, Karl Aberer, Manfred Hauswirth Date: Published by IP: IP5 Document: public Attachments: public Doc. Reference: Poster04-1 Owner Group: IP5

5 Goal Creating a scalable semantic P2P system supporting local schema creation while enforcing global semantic interoperability

6 Our proposition: GridVine Principle of data independence –Scalable physical layer –Semantic logical layer Semantic Gossiping (Chatty Web)

7 2. P-Grid Virtual, distributed binary search tree Totally decentralized, scalable, self-organizing access structure –Search-cost: O(log(n)) hops (even for unbalanced trees) Dynamic load-balancing Key-based searches –Prefix searches –Range searches Decentrlized public key infrastructure Freely available implementation 

8 3. GridVine: annotating shared resources End-users create annotations / ”categories” / ”translation links” –Constraining the annotation mechanism We do not expect them to write ontologies, views… Annotations –Predicate + value w.r.t. shared resource Categories –Atomic classes –Semi-structured collections of properties –No constraint on semantics of the hierarchies (mereologic? taxonomic?) –Possibility to derive (extend) sub-categories from super- categories Translation links –Relate properties from one schema to another

9 GridVine (2) Support of Semantic Web standards –RDF annotations –RDFS categories –OWL translation links <rdf:Description rdf:about="urn:x-pgrid:F59F92C8BC…lucene_green_100.gif">

10 Mapping annotations onto P-Grid 00?01?10?11? 0??1?? ??? <rdf:Description rdf:about="urn:x- pgrid:F59F92C8BC…lucene_green_100.gif"> 2001 User-defined annotations (RDF triples) User-defined categories (RDFS) User-defined category translations (OWL) Flexible (sub)string searches on –Annotations Subject, Predicate, Object –Categories Creator + name –Translations Category names  RDQL queries P-Grid

11 Semantic Interoperability (1): Creating sub-categories Super-category subsumed by sub-category Fostering semantic interoperability through reuse of conceptualizations Few popular base categories  Semantic interoperability on base properties

Semantic Interoperability (2): Semantic Gossiping (Chatty Web) Author Creator WinFS Images peers Author, Keyword… Photoshop Images peers Creator, Subject … Familiy X Images peer Event Creator  Event Creator  Author Author  Creator Why creating translation links? –Local mappings enabling global agreements  Extending traditional data integration techniques (e.g., LAV/GAV) to decentralized settings

13 Semantic Interoperability (2): Semantic Gossiping (Chatty Web) Heterogeneous, decentralized setting –Heterogeneous categories –Few really equivalent classes Local PHBs to forward queries iteratively –Distance(query, mapping(mapping…(query))) –Syntactic distance Information (e.g., predicates) lost –Semantic distances: agreements on mappings Analysis of transitive closure of mappings –Results Analysis –Cycles Analysis Forwarding stops when Distance>Threshold  Query forwarding by selecting the right links Experimental Results: cf. Journ. Web Semantics 1(1)

14 Traversals of the Semantic Overlay Network GridVine: structured P2P network! Distributed index! –No more constraints on gossiping Different query forwarding paradigms –Iterative forwarding –Recursive forwarding

15 4. Demo

16 5. Conclusions GridVine –Based on a scalable, decentralized access structure –Supports local creation of schemas –Fosters global semantic interoperability through schema inheritance and Semantic Gossiping On-going efforts –Implementation… –Improved GUI standard property values, property value types… –Richer (?) translation links syntactic / semantic constructs –Automatic creation / correction of schemas Cf. PicShark -- joint project with Microsoft Research –Deployment on PlanetLab

17 Some References… P-Grid P-Grid: A Self-Organizing Access Structure for P2P Information Systems Karl Aberer Cooperative Information Systems (CoopIS 2001), Trento, Italy Improving Data Access in P2P Systems Karl Aberer, Manfred Hauswirth, Magdalena Punceva, Roman Schmidt IEEE Internet Computing, 6(1), January/February P-Grid: A Self-organizing Structured P2P System Karl Aberer, Philippe Cudré-Mauroux, Anwitaman Datta, Zoran Despotovic, Manfred Hauswirth, Magdalena Punceva, Roman Schmidt SIGMOD Record, 32(2), September Semantic Gossiping A Framework for Semantic Gossiping Karl Aberer, Philippe Cudré-Mauroux, Manfred Hauswirth SIGMOD Record, 31(4), December The Chatty Web: Emergent Semantics through Gossiping Karl Aberer, Philippe Cudré-Mauroux, Manfred Hauswirth, International World Wide Web Conference (WWW03), Budapest, Hungary Start making sense: The Chatty Web approach for global semantic agreements Karl Aberer, Philippe Cudré-Mauroux, Manfred Hauswirth, Journal of Web Semantics, 1 (1), December 2003.