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Super-Peer-Based Routing and Clustering Strategies
forRDF-Based Peer-To-Peer Networks
Alexander Löser
Technische Universität Berlin, Germany
Wolfgang Nejdl, Martin Wolpers, Wolf Siberski, Christoph Schmitz, Mario Schlosser, Ingo Brunkhorst
Learning Lab Lower Saxony,Hannover/Karlsruhe, Germany
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3
PADLR: Personalized Access to Digital Learning Resources
Heterogeneous Applicatio
ns Repositori
es Platforms
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4
Edutella: Introduction
Main Goal: Achieve interoperability between heterogeneous metadata-driven (e-learning) systems
Provides metadata only, not the resources resources are fetched via http
Foundations Semantic Web Peer-to-Peer Federated Databases
Open source project (http://edutella.jxta.org) Uses other OSS: JXTA Platform, Jena, JUnit, Ant
Uses: Xerces, Jetty, ICU4J, XIndice, ...
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6
Schema-Based Peer-to-Peer Networks
User-definable schemas Structured schemas Query language
(system list not complete)
No central control Node autonomy Self organization
Database Systems
P2P
Sys
tem
s
Schema-based P2PSystems
schema-based
peer-to-peer
CANCHORD
DIRECTCONNECT
GNUTELLA
KAZAAP-GRID
NAPSTER
AMOSIIOBJECTGLOBE
TSIMMISTUKWILA
CHATTY WEB
EDUTELLA
PIAZZA
ANY RDBMSCONCEPTBASE
ONTOBROKER
fixedschema/
keywords
key
local distributed
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7
Problem and Approach
Broadcasting all queries to all information sources obviously doesn‘t scale
Problem: How to distribute queries in a scalable fashion?
Optimal solution: distribute a query only to peers which have results for it
Approach Use Super-Peer network Introduce Query Routing Indices
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8
Super-Peer Networks
Observation: Peers vary significantly in availability, bandwith, processing power, etc.
Create network backbone from highly available and powerful peers to distribute load better.
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0
0
10
1
11
0
2
2 2
2
SP1
Super-Peer Topology
Super-peers are arranged as HyperCuP
Broadcast needs n-1 messages, log2(n) hops
High connectivity, resilient against node failures
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Routing Indices
On joining the network, each peer provides self-description
Based on this information, super-peers maintain indexes of schemas/schema elements used at each peer
Super-peer/peer indices Super-peer/super-peer indices
Index Granularity Schema Property Property + value range Property + individual values
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0
0
10
1
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0
2
2 2
2
SP1
SP3
SP2
SP4
P0
P1
P4
P2 P3
dc:languagelom:contextdc:subject
„de“„undergrad“ccs:sw-eng
<s><s><s>
dc:languagelom:contextdc:subject
„de“„undergrad“ccs:sw-eng
<r><r><r>
dc:subject ccs:ethernet<p> dc:subject ccs:clientserver<p>
Index Sample
...
dc SP1, SP3,SP4
lom SP1,SP4
SP2
lom:context P1
dc:subject ccs:sw-eng P1
dc:language „de“ P1
...
SP1
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0
0
10
1
11
0
2
2 2
2
SP1
SP3
SP2
SP4
P0
P1
P4
P2 P3
dc:languagelom:contextdc:subject
„de“„undergrad“ccs:sw-eng
<s><s><s>
dc:languagelom:contextdc:subject
„de“„undergrad“ccs:sw-eng
<r><r><r>
dc:subject ccs:ethernet<p> dc:subject ccs:clientserver<p>
Query Routing Sample
Find any resource with dc:subject=ccs:sw-eng and lom:context=“undergrad”
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13
Clustering
If peers are randomly assigned to super-peers, we often still have to broadcast queries within the super-peer network
Two approaches: Static: super-peer administrators define constraints which
peers have to fulfill to be accepted Dynamic: based on query statistics, peers are continually
reassigned to optimize query distribution
Work in progress
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14
Schema Mapping
Peers may use different schemas to annotate their resources
Use federated database techniques for mapping Super-peers acts as Mediators Mapping rules have to be specified manually
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15
Super-peer/Peer implementationB
ind
Ser
vice
Ad
v
Qu
ery
Ser
vice
Ad
v
Ro
urt
ing
Ser
vice
Ad
v
QueryService
JXTAEndpoint
Routing Service
Peer Service Registry
BindingService
ExecutionPool
JXTAEndpoint
ExecutionPool
JXTA Endpoint
SP/SPRouting
Processor
ExecutionPool
ExecutionPool
SP/PRouting
Processor
Bind Service Routing Service Query Service
SP/P RIs
QueryProcessor
BindingProcessor
To
po
log
y S
ervi
ce A
dv
JXTAEndpoint
TopologyService
Topology Service
SP/SP RIs
PeerSuper-Peer
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16
Further Work
Quantitative evaluation (by simulation) Exploration of clustering approaches Integration of other mediation techniques