Table of Contents

1  The Semantic Web   1

1.1 What is the Semantic Web? 3

Indexing and retrieving information 5

Meta data 5

Annotation 6

A huge interoperable database 6

Machine retrieval of data 6

Services 7

Discovery 7

Intelligent agents 8

1.2 Two Semantic Web scenarios 8

Can the Semantic Web work this way? 10

1.3 The Semantic Web’s foundation 10

Resources 11

Standardized addressing 11

Small set of commands 12

Scalability and large networks 12

Openness, completeness, and consistency 13

The Web and the Semantic Web 13

1.4 The Semantic Web layer cake 14

The base 16

Properties and relationships 17

Analysis, verification, and trust 17

1.5 Summary 18

2  Describing data with RDF   19

2.1 Introducing RDF 22

Some terminology 22

Identifying resources 23

Anonymous resources 25

RDF and conventional databases 25

2.2 Working with RDF properties 28

Properties as resources 28

Names, labels, and identifiers 29

Properties of statements 30

2.3 Visualizing statements with RDF graphs 30

Resources with many statements 31

Anonymous nodes 32

Resources as objects of statements 33

Container nodes 34

Graphing properties of statements 35

2.4 Six RDF applications 37

RDF in Mozilla 37

RSS 37

RDF for annotations: Annotea 38

Bibliographic meta data: Dublin Core 39

WebScripter: fusing information 39

Haystack: personal information management 40

2.5 Meshing data and meta data 41

The data model 41

The data in table format 42

The relationships between tables 43

The RDF version of the data 44

Table versions of the data 46

Why bother with RDF? 47

2.6 Sharing data 47

RDF/XML syntax 48

Non-XML formats 56

2.7 RDF in the real world of the Web 56

What does a URI reference indicate? 56

Contradictory statements 58

Incomplete information 58

Limitations 58

2.8 Summary 59

3  Navigating information with topic maps   60

3.1 What are topic maps? 61

An example index 62

The subject of a topic 66

Properties 68

Scopes 69

Summary of key features 70

Collocation, navigation, and representation of information 70

Merging topic maps 71

Maturity of Topic Maps software 72

3.2 Basic models of topic maps 72

Abstract model 73

Implementation approaches 77

3.3 Sharing topic maps between computers 78

3.4 Topic map examples 79

Weather events 80

Conference proceedings 81

3.5 Topic maps and the Web 82

3.6 Topic maps and RDF 84

RDF: information by the atom 84

Topic maps: proteins of knowledge 85

The subject, revisited 85

Theoretical basis 86

Data structures as first-class citizens 86

Strengths and weaknesses 86

3.7 How topic maps are used in practice 87

3.8 Summary 88

4  Annotation   90

4.1 What is annotation? 91

4.2 Annotations at full power 92

4.3 Current web annotation systems 94

Wiki collaboratives 95

Annotea 96

Multivalent browser 99

4.4 Improving annotation 103

4.5 Summary 105

5  Searching   106

5.1 Searching the Web 108

Kinds of searches 108

So near and yet so far 109

Behind the scenes 110

5.2 Search strategies 112

Keywords 112

Ontologies 113

Meta data 114

Semantic analysis 114

Semantic focusing 117

Social analysis 118

Multiple passes 120

Peer to peer 120

Clustering 121

5.3 Distorting results and spoofing search engines 123

5.4 Searching and the Semantic Web 124

Self-describing meta data: no panacea 124

Semantic Web possibilities for improving searching 124

Searching and web services 125

5.5 Summary 126

6  The role of logic   127

6.1 What logic is good for 128

Rules 129

Inferring facts 130

Explanations 131

Contradictions and interpretations 131

Ontologies 133

The representation of knowledge 134

Queries 134

Combining information 135

6.2 All logics aren’t created equal 135

First-order logic: the logic of individual things 136

Second-order logic: the logic of types and relationships 136

Finessing complexity 137

Life beyond first-order logic 137

6.3 Two pitfalls 138

Don’t swallow the whole Web 138

Knowledge pollution 139

6.4 Patchwork quilt or seamless whole? 139

6.5 Summary 140

7  Ontology   141

7.1 Basic classification 143

Lists, hierarchies, and trees 143

Classification groups 145

7.2 Arranging names 148

Names and identifiers 148

Properties 149

7.3 Building ontologies 150

Frameworks 151

On designing ontologies 151

Other considerations 152

7.4 Languages for ontologies 155

RDFS 155

OWL 161

DAML + OIL 168

7.5 Summary 169

8  Semantic Web services   170

8.1 What are web services? 171

Web pages as services 172

Beyond the plain web page 172

How semantic are today’s web services? 173

Elements of web services 173

8.2 Exchanging data 174

Web only? 175

To RDF or not? 175

SOAP 175

RDF with SOAP 177

HTML forms 177

8.3 Invoking services 178

Using HTTP for web services 178

About HTTP messages 178

Remote procedure calls 181

The Web versus RPC 181

The RPC controversy 184

8.4 Describing and finding services 186

Connecting to services 186

Discovering services 194

Describing web service processes 198

8.5 Will web services converge with the Semantic Web? 201

8.6 Summary 202

9  Agents   204

9.1 What is an intelligent agent? 205

9.2 Agents at work 207

9.3 Basic agent types 207

Logic-based agents 208

Reactive agents 209

Belief-desire-intention agents 209

Layered architectures 209

9.4 Agent interactions 210

9.5 Agents on the Semantic Web 212

Beyond factory agents 212

Agent evolution 213

9.6 Frameworks and standards 213

Foundation for Intelligent Physical Agents 213

FIPA-OS and other FIPA implementations 215

Java Agent Services 217

9.7 Summary 217

10  Distributed trust and belief   219

10.1 The territory 221

10.2 Tools of trust 222

Private keys 222

Public keys 223

Digests 223

Public Key Infrastructure 223

Digital signing 227

A trust scorecard 228

10.3 Reliable and believable? 229

All statements aren’t equal 230

Handling contradictory information 230

Dealing with information of uncertain reliability 231

10.4 Agents and the Web of Trust 233

10.5 Summary 234

11  Putting it all together   236

11.1 Just what is the Semantic Web? 237

11.2 Scenarios redux 238

The first scenario 238

The second scenario 242

The scenarios in perspective 244

11.3 Some Key Issues 244

Scalability 245

Ontologies—universal or piecework 245

Identity 246

Strong AI and the role of logical reasoning 247

Embedded semantic markup 247

Web services and the Semantic Web 248

Trust, belief, and confidence 248

11.4 How semantic will it be? 249

11.5 Can it really come about? 250

The technology front 250

Plugging in 251

Growing the Semantic Web 254

Appendix  Case studies   256

A.1 FOAF: Friend of a Friend 257

Sharing a bit of yourself 257

A FOAF example 258

Identification without universal IDs 259

Board of a board 260

Lessons 262

A.2 Browser bookmarks 262

Goals for the case study 263

Conventional bookmark managers 263

Modeling the bookmark collection 264

Simple means 268

A.3 Reflections on the case studies 268

references 269
index 275