Preface	6
	Contents	9
	Peer-to-Peer and Semantic Web	12
	1 The Semantic Web	12
	1.1 Infrastructure for Machine-Readable Metadata	13
	1.2 Representing Local and Shared Meaning	13
	2 Peer-to-Peer	14
	2.1 Peer-to-Peer and Knowledge Management	15
	2.2 Peer-to-Peer and the (Semantic) Web	17
	3 Aspects of Semantics-Based Peer-to-Peer Systems	17
	3.1 Data Storage and Access	18
	3.2 Querying the Network	20
	3.3 Integration Mechanism	22
	3.4 Building and Maintaining Semantic P2P Applications	25
	3.5 Other Issues	26
	4 Conclusions	27
	References	27
	Part I Data Storage and Access	29
	Overview: Data Storage and Access	30
	1 An RDF Query and Transformation Language	32
	1.1 Introduction	32
	1.2 Query Language requirements	33
	1.2.1 Expressive power	33
	1.2.2 Schema awareness	34
	1.2.3 Program manipulation	34
	1.2.4 Compositionality	34
	1.2.5 Semantics	34
	1.3 The Syntax of SeRQL	35
	1.3.1 Path Expressions	35
	1.3.2 Filters and operators	39
	1.4 Formal Interpretation of SeRQL	40
	1.4.1 Mapping Basic Path Expressions to Sets	40
	1.4.2 Functions	42
	1.4.3 Reducing Composed Expressions	44
	1.5 Related work	45
	1.6 Conclusions	46
	References	46
	2 RDF and Traditional Query Architectures	49
	2.1 Introduction	49
	2.2 Motivation	50
	2.3 Hierarchical mediator architecture	52
	2.3.1 Indexing Sources	54
	2.3.2 Index Creation and Maintenance	54
	2.3.3 Query Planning and Optimization	56
	2.3.4 Object Identity	56
	2.3.5 HMA Advantages and Limitations	57
	2.4 Cooperative Mediator Architecture	59
	2.4.1 Paradigm Shift	59
	2.4.2 Query Processing and Query Optimization	60
	2.4.3 Making the Query Plan Robust	61
	2.5 Summary and Discussion	63
	References	64
	3 Query Processing in RDF/S-Based P2P Database Systems	67
	3.1 Introduction	67
	3.2 The SQPeer Middleware	69
	3.2.1 RDF/S-based P2P databases and RQL Queries	70
	3.2.2 RVL Advertisements of Peer Bases	71
	3.2.3 Query Routing and Fragmentation	73
	3.2.4 Query Planning and Execution	74
	3.2.5 Query Optimization	76
	3.3 P2P Architectures and SQPeer	79
	3.3.1 Hybrid P2P SONs	80
	3.3.2 Structured P2P SONs	82
	3.4 Related Work	84
	3.5 Summary	86
	References	87
	Part II Querying the Network	90
	Overview: Querying the Network	91
	4 Cayley DHTs - A Group-Theoretic Framework for Analyzing DHTs Based on Cayley Graphs	94
	4.1 DHTs and Static DHT Topologies	94
	4.2 Cayley DHTs - A Group-Theoretic Model for Analyzing DHTs	95
	4.2.1 Groups and Cayley Graphs	95
	4.2.2 Non-constant Degree Cayley DHTs	96
	4.2.3 Constant Degree Cayley DHTs	98
	4.2.4 Non-Cayley DHTs	102
	4.3 Cayley Graph Properties and DHTs	102
	4.3.1 Symmetry and Load Balancing	102
	4.3.2 Hierarchy, Fault Tolerance, and Proximity	104
	4.3.3 Connectivity and Fault Tolerance	104
	4.3.4 Hamiltonicity and Cyclic Routing	106
	4.4 Discussion and Related Work	106
	4.5 Conclusions	108
	References	108
	5 Semantic Query Routing in Unstructured Networks Using Social Metaphors	111
	5.1 Introduction	111
	5.2 SWAP Platform	113
	5.2.1 Meta-information	113
	5.2.2 Querying for Data	114
	5.3 Algorithm	114
	5.3.1 The Social Metaphors	114
	5.3.2 Protocol Scenario	115
	5.3.3 Peer selection algorithm	116
	5.4 Evaluation Setting	117
	5.4.1 Data Source and Peer setup	117
	5.4.2 Generation of queries in experiment	118
	5.4.3 Initial con.guration of the Peer-to-Peer network simulation	118
	5.4.4 Evaluation measures	119
	5.5 Results	120
	5.5.1 Hypotheses	120
	5.5.2 Evaluation	120
	5.6 Related Work	124
	5.7 Conclusion	125
	References	125
	6 Expertise-Based Peer Selection	128
	6.1 Introduction	128
	6.2 Related Work on Semantic Overlay Networks	129
	6.3 A Model for Expertise Based Peer Selection	131
	6.3.1 Semantic Description of Expertise	131
	6.3.2 Matching and Peer Selection	132
	6.3.3 Semantic Overlay	132
	6.4 Expertise Based Peer Selection in Bibster	133
	6.5 Results of Simulation Experiments	135
	6.6 Results of Field Study	141
	6.7 Comparison with Results from Simulation Experiments	142
	6.8 Conclusion	143
	References	144
	7 Personalized Information Access in a Bibliographic Peer-to-Peer System	146
	7.1 Introduction	146
	7.1.1 Example Scenarios	147
	7.2 Ontology Based Similarity	148
	7.2.1 The Bibliographic Ontologies	148
	7.2.2 Semantic Similarity	150
	7.3 Semantic User Profile	153
	7.3.1 User Profile Representation	153
	7.3.2 Initial User Profile and Profile Adaptation	155
	7.4 Recommender Functions	156
	7.4.1 Recommending Similar Items	156
	7.4.2 Recommending Potentially Relevant Items	157
	7.4.3 Recommending Similar Peers	157
	7.5 Related Work	158
	7.6 Conclusion	159
	References	159
	8 Designing Semantic Publish/Subscribe Networks Using Super-Peers	161
	8.1 Introduction	161
	8.2 A Formalism for Pub/Sub Systems Based on RDF	162
	8.3 The Super-Peer Architecture	165
	8.4 Processing Advertisements, Subscriptions and Notifications	168
	8.4.1 Processing Advertisements	168
	8.4.2 Processing Subscriptions	171
	8.4.3 Processing Notifications	172
	8.5 Dynamics of P2P Pub/Sub Networks	173
	8.5.1 Of.ine Noti.cations and Rendezvous at Super-Peers	173
	8.5.2 Peer Authentication	174
	8.6 Related Work	176
	8.7 Conclusions	177
	8.8 Acknowledgements	178
	References	178
	Part III Semantic Integration	182
	Overview: Semantic Integration	183
	9 Semantic Coordination of Heterogeneous Classifications Schemas	185
	9.1 Introduction	185
	9.2 Our Approach	186
	9.3 The Algorithm:	189
	9.3.1 Semantic Elicitation	192
	9.3.2 Semantic Comparison	194
	9.4 Related Work	195
	9.5 Conclusions	197
	References	198
	10 Semantic Mapping by Approximation	201
	10.1 Introduction	201
	10.2 Application in Peer-to-Peer	203
	10.3 Internet Music Schemas	205
	10.4 Approximate Matching	206
	10.4.1 Normal Forms	207
	10.5 Experiment with Approximate Matching	208
	10.5.1 Example of an Approximate Matching	209
	10.5.2 Comparison with Instance Data	210
	10.6 Future Work	212
	10.6.1 Improvements of Approximation Accuracy	213
	10.6.2 Sources of Background Knowledge	213
	10.7 Conclusion	214
	Acknowledgements	214
	References	214
	11 Satisficing Ontology Mapping	216
	11.1 Introduction	216
	11.2 Terminology	218
	11.2.1 Ontology	218
	11.2.2 Mapping	218
	11.2.3 Example	218
	11.3 Process	219
	1. Feature engineering	219
	2. Selection of Next Search Steps.	219
	3. Similarity Computation	219
	4. Similarity Aggregation.	219
	5. Interpretation	220
	6. Iteration.	220
	11.4 A Toolbox of Data Structures and Methods	220
	11.4.1 Features of Ontological Entities	220
	11.4.2 Similarity Computation	221
	11.4.3 Similarity Aggregation	222
	11.4.4 Interpretation	222
	11.5 Approaches to Determine Mappings	222
	11.5.1 Standard Mapping Approaches	222
	11.5.2 QOM - Quick Ontology Mapping	224
	11.6 Comparing Run-time Complexity	226
	11.7 Empirical Evaluation and Results	227
	11.7.1 Test Scenario Metrics	227
	11.7.2 Results and Discussion	228
	11.8 Related Work	230
	11.9 Conclusion	230
	References	231
	12 Scalable, Peer-Based Mediation Across XML Schemas and Ontologies	233
	12.1 Introduction	233
	12.2 System Overview	235
	12.2.1 Data, Schemas, and Queries	235
	12.2.2 Data Sharing and Mediation	237
	12.2.3 Query Processing	237
	12.3 Mapping Requirements for Structured Data	238
	12.4 Schema Mappings in Piazza	239
	12.4.1 Mapping Language and Examples	241
	12.4.2 Semantics of Mappings	245
	12.4.3 Discussion	246
	12.5 Query Answering Algorithm	247
	12.5.1 Query Representation	248
	12.5.2 The Rewriting Algorithm	250
	12.6 Conclusions and Future Work	254
	References	254
	13 Semantic Gossiping: Fostering Semantic Interoperability in Peer Data Management Systems	257
	13.1 Introduction	257
	13.2 Motivation: Sharing Images Meaningfully	259
	13.3 Of Semantic Neighborhoods and Schema Translations	261
	13.4 Semantic Query Routing	263
	13.4.1 Syntactic Measures	263
	13.4.2 Semantic Measures	264
	13.4.3 An illustrating example	266
	13.5 Self-Healing Semantic Networks	267
	13.6 Analyzing Semantic Interoperability in the Large	269
	13.7 GridVine: Implementing Semantic Gossiping on top of a DHT	270
	13.8 Conclusions	272
	References	273
	Part IV Methodology and Systems	274
	Overview: Methodology and Systems	275
	References	277
	14 A Methodology for Distributed Knowledge Management Using Ontologies and Peer-to-Peer	279
	14.1 Introduction	279
	14.2 The Theory of Distributed Knowledge Management	281
	14.3 Methods for Distributed Knowledge Management	284
	14.4 Tools for Distributed Knowledge Management	287
	14.4.1 Analysis	288
	14.4.2 Design	290
	14.4.3 Deployment	293
	14.4.4 Evaluation	294
	14.5 Summary	296
	References	297
	15 Distributed Engineering of Ontologies (DILIGENT)	299
	15.1 Introduction and Motivation	299
	15.2 DILIGENT Process	300
	15.3 AIFB Case Study: An Argumentation Framework for DILIGENT	302
	15.3.1 Threads of Arguments	302
	15.3.2 Hypothesis	303
	15.3.3 Hypothesis Validation	304
	15.4 IBIT Case Study: a running DILIGENT Process	308
	15.4.1 Organizational Setting	308
	15.4.2 Technical Setting	309
	15.4.3 Realizing a DILIGENT Process	309
	15.4.4 Lessons Learned from the Realization	311
	15.4.5 Tool Support for DILIGENT Steps	311
	15.5 Related Work	316
	15.6 Conclusion	316
	References	317
	16 A Peer-to-Peer Solution for Distributed Knowledge Management	319
	16.1 Introduction	319
	16.2 KEx: a P2P Architecture for DKM	320
	16.2.1 K-peers	320
	16.2.2 Roles of K-peers in KEx	323
	16.2.3 K-Services	324
	16.3 Development Framework	327
	16.4 Conclusions and Research Issues	328
	References	329
	17 Xarop, a Semantic Peer-to-Peer System for a Virtual Organization	331
	17.1 Introduction	331
	17.1.1 The Tourism Sector in the Balearic Islands	331
	17.1.2 Decision making in the Destination	332
	17.1.3 Domains of Knowledge	333
	17.2 Requirements Analysis	335
	17.2.1 Organizational Context Analysis	336
	17.2.2 Use Cases Description Searching for Information	337
	17.3 XAROP platform description	338
	17.3.1 Knowledge Providing functionalities	339
	17.3.2 Knowledge Searching Functionalities	340
	17.3.3 Managing Security Permissions	341
	17.4 Conclusions	341
	References	342
	18 Bibster - A Semantics-Based Bibliographic Peer-to-Peer System	344
	18.1 Introduction	344
	18.2 Major Use Cases for Bibster	345
	18.3 Design of Bibster	346
	18.3.1 Ontologies in Bibster	346
	18.3.2 Bibster Architecture and Modules	347
	18.4 Semantic Extraction of Bibliographic Metadata	349
	18.5 Semantic Querying	350
	18.6 Expertise Based Peer Selection	352
	18.7 Semantic Duplicate Detection	354
	18.8 Results	355
	18.9 Related Work	357
	18.10 Conclusion	357
	References	358
	Author Index	359