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ISWC04 11.11.04

GridVine: Building Internet-Scale Semantic Overlay

NetworksKarl Aberer, Philippe Cudré-Mauroux, Manfred Hauswirth

School of Computer and Communication Sciences (I&C)Swiss Federal Institute of Technology (EPFL)

Tim van PeltDepartment of Computer and Information Science

Linköpings Universitet, Sweden

NCCR-MICS KnowledgeWeb

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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. Demo5. Conclusions

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1. Motivations

• Schema-based searches in P2P networks

– Fixed set of schemas• Ok for searching mp3s, trailers…

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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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 SettingsAuthors: Philippe Cudre-Mauroux, Karl Aberer, Manfred HauswirthDate: 4 11 2004Published by IP: IP5Document: publicAttachments: publicDoc. Reference: Poster04-1Owner Group: IP5

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Goal

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

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Our proposition: GridVine

• Principle of data independence– Scalable physical layer– Semantic logical layer

• Semantic Gossiping (Chatty Web)

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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

www.p-grid.org

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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

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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"> <Year xmlns="pgrids://CF0C052CE4…Pdf.rdfs#">2001</Year></rdf:Description>

<rdfs:Class rdf:ID="Pdf" rdfs:comment="New schema class"> <rdfs:subClassOf rdf:resource="http://www.p-grid.org/p-grid.rdfs#PGridDataFile"/></rdfs:Class>

<rdf:Property rdf:ID="Year"> <rdfs:domain rdf:resource="#Pdf"/> <rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema#string"/></rdf:Property>

<Title xmlns="pgrids://CF0C052…PDFFIle.rdfs#”> <owl:equivalentProperty rdf:ID=“map1” rdf:resource="pgrids://AF..Pdf.rdfs#Titre" /></Title> <rdf:Description rdf:about=“#map1" /> <pgrids://owl/CycleAnalysis> 0.7 </pgrids://owl/CycleAnalysis></rdf:Description>

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Mapping annotations onto P-Grid

00? 01? 10? 11?

0?? 1??

???

000 010 100 011

<rdf:Description rdf:about="urn:x-pgrid:F59F92C8BC…lucene_green_100.gif"> <Year xmlns="pgrids://CF0C052CE4…Pdf.rdfs#">2001</Year></rdf:Description>

User-defined annotations (RDF triples)

<rdfs:Class rdf:ID="Pdf" rdfs:comment="New schema class"> <rdfs:subClassOf rdf:resource="http://www.p-grid.org/p-grid.rdfs#PGridDataFile"/></rdfs:Class><rdf:Property rdf:ID="Year"> <rdfs:domain rdf:resource="#Pdf"/> <rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema#string"/></rdf:Property>

User-defined categories (RDFS)<Title xmlns="pgrids://CF0C052CE418FC78…PDFFIle.rdfs#"> <owl:equivalentProperty rdf:resource="pgrids://CF…Pdf.rdfs#Title" /> <rdf:Statement> <rdf:subject rdf:resource="pgrids://CF0…PDFFIle.rdfs#Title" /> <rdf:predicate rdf:resource="pgrids://owl/hasCorrectness" /> <rdf:object rdf:resource="1.0" /> </rdf:Statement></Title>

User-defined category translations (OWL)

• Flexible (sub)string searches on– Annotations

• Subject, Predicate, Object

– Categories • Creator + name

– Translations• Category names

RDQL queries

P-Grid

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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

Author

Creator

Creator

Creator

WinFS Images peersAuthor, Keyword…

Photoshop Images peersCreator, Subject …

Familiy X Images peerEvent

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

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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)

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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

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4. Demo

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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

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Some References…

P-GridP-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 2002.

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 2003.

Semantic Gossiping A Framework for Semantic Gossiping Karl Aberer, Philippe Cudré-Mauroux, Manfred HauswirthSIGMOD Record, 31(4), December 2002.

The Chatty Web: Emergent Semantics through GossipingKarl 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.