Peer-to-Peer Data Integration Using Distributed Bridges Neal Arthorne B. Eng. Computer Systems (2002) Supervisor: Babak Esfandiari April 12, 2005 Candidate Thesis for M. A. Sc. in Electrical Engineering

2 Introduction Multiple autonomous heterogeneous data sources  E.g. chemistry and genetics databases, digital repositories, astronomy databases Data is distributed and network-accessible Each data source may use a different syntax or query language (SQL, Web Services etc.)

3 Related Work Federated database systems [Sheth, 1990]  Global federated schema Mediator approach [Wiederhold, 1992]  Databases wrapped in a software layer that translates to a common information model  Middleware lies between user applications and data sources Theoretical description of data integration  Schemas mapped with FOL statements – LAV or GAV approach

4 Related Work Cont’d OWL/RDF/RDFS used to describe semantic relationships – ontologies Peer-to-Peer Data Integration – WWW approach to integrating data  PIAZZA (Halevy et al.), Lenzerini, Franconi  Focused on query optimization and decidability in FOL systems

5 Limitations of Related Work Global shared schemas are fragile and not scalable  Centrally located and administered  Changes affect all component databases or middleware P2P data integration is limited  Semantic differences not addressed  Centrally stored mappings  Large databases not compatible with centralized metadata

6 Proposed Solutions User-contributed mappings between schemas (bridges) Fully de-centralized distribution of mappings  Anyone can publish a new mapping  No global schema means improved scalability Provide semantic mappings for data Distributed searching compatible with large databases Use existing Universal Peer-to-Peer (U-P2P) framework

7 Universal Peer-to-Peer (U-P2P) Peers share XML metadata with binary attachments Communities formed around a shared XML Schema Community itself is published – anyone can create a community Flexible deployment – pluggable Network Adapters 0..* Resource Attachments Book Comunity War & Peace file:// * 1 1

8 P2P Data Integration with U-P2P Proposed Bridge Community and bridge schema  Anyone can publish a bridge  Includes simple semantic relation  Attached mappings and/or transforms U-P2P modularized for database proxies Distributed Network Adapter (Gnutella)  Compatible with large databases  No central indexing servers

9 > Shareable Bridges in U-P2P ResourceCommunityBridge 1 0..* Semantic relation - Data mappings

10 Example Bridge DSpace to Fedora bridge … d2a9d6f78dcf91828f68a52f78260e05 134d8f8ecd57acb35206b4cd13e38622 owl:sameAs d2a9d6f78dcf91828f68a52f78260e05 da b7d8890fc7df7f879a0a7db file://… Bridge Source Bridge Target OWL Relation Transform attachments

11 Case Study: Digital Repositories Peer A Peer B Peer C DSpace Community Fedora Community DSpace Community Fedora Community Fedora Community Generic Central Server Gnutella ProtocolCentralized P2P Fedora Database Proxy Bridge

12 Conclusion P2P approach to integration – anyone can create a bridge Fully-distributed network adapter brings in large data sources via proxies Demonstrated integration with digital repositories  Simple semantic relationship (OWL)  Query translation

13 Future Work Manual navigation between schemas  Need to automate retrieving bridges XPath query translation is limited  Need to provide robust query translation modules  Translate instance data Semantic relationships not exploited  Use OWL ontologies to give bridges a context  Software agents can be introduced to discover and use bridges