Semantic Web Programming

Foreword xxiii

Introduction xxv

Part One Introducing Semantic Web Programming 1

Chapter 1 Preparing to Program a Semantic Web of Data 3

Defining the Semantic Web 4

Identifying the Major Programming Components 10

Determining Impacts on Programming 13

Establishing a Web Data–Centric Perspective 13

Expressing Semantic Data 14

Sharing Data 16

Making Data Dynamic and Flexible 18

Avoiding the Roadblocks, Myths, and Hype 19

Semantic Web Roadblocks 19

Semantic Web Myths 21

Semantic Web Hype 22

Understanding Semantic Web Origins 23

Exploring Semantic Web Examples 26

Semantic Wikis (semantic-mediawiki.org) 26

Twine (www.twine.com) 27

The FOAF Project (www.foaf-project.org) 28

RDFa and Microformats 30

Semantic Query Endpoint (dbpedia.org/sparql) 32

Semantic Search (www.trueknowledge.com) 32

Summary and Onward 34

Notes 34

Chapter 2 Hello Semantic Web World 35

Setting Up Your Semantic Web Development Environment 36

Programming the Hello Semantic Web World Application 38

Summary 58

Part Two Foundations of Semantic Web Programming 61

Chapter 3 Modeling Information 63

Modeling Information in Software 64

Sharing Information: Syntax and Semantics 65

Serialized Objects 66

Relational Databases 66

Extensible Markup Language (XML) 66

Metadata and Data in Information Sharing 67

The Semantic Web Information Model: The Resource Description Framework (RDF) 68

Nodes: Resources and Literals 69

Edges: Predicates 71

Exchanging Information with RDF 72

Statements as Points 73

RDF Serializations 74

RDF/XML 74

Terse RDF Triple Language (Turtle) 78

N-Triples 81

Quick Hack 82

More RDF 84

Blank Nodes 84

Reification 88

RDF Organizational Constructs 88

Summary 91

Chapter 4 Incorporating Semantics 93

Semantics on the Web 94

Motivating Factors 94

Understanding the World WideWeb 95

Knowledge Domain Integration 97

Expressing Semantics in RDF 98

Vocabularies, Taxonomies, and Ontologies 99

A Vocabulary Language for RDF 100

An Ontology Language for the Web 101

Introduction to Ontologies 102

Distributed Knowledge 102

Open World Assumption 103

No Unique Names Assumption 104

Overview of Ontology Elements 104

Ontology Header 105

Classes and Individuals 105

Properties 106

Annotations 106

Data types 106

Elements of an Ontology 107

OWL 2 Typing 107

Ontology Header 108

Annotations 109

Basic Classification 110

Classes and Individuals 110

rdfs:SubClassOf 111

Instance versus Subclass 112

owl:Thing and owl:Nothing 113

Defining and Using Properties 113

Property Domain and Range 114

Describing Properties 115

rdfs:subPropertyOf 115

Top and Bottom Properties 116

Inverse Properties 116

Disjoint Properties 117

Property Chains 118

Symmetric, Reflexive, and Transitive Properties 119

Functional and Inverse Functional Properties 120

Keys 121

Datatypes 122

Data type Restrictions 122

Defining Datatypes in Terms of Other Datatypes 124

Negative Property Assertions 126

Property Restrictions 127

Value Restrictions 127

Cardinality Restrictions 130

Qualified Cardinality Restrictions 132

Advanced Class Description 134

Enumerating Class Membership 134

Set Operators 134

Disjoint Classes 136

Equivalence in OWL 137

Equivalence among Individuals 138

Equivalence among Classes and Properties 139

Summary 139

Chapter 5 Modeling Knowledge in the Real World 141

Exploring the Components of the Semantic Web 141

Semantic Web Frameworks 143

Storing and Retrieving RDF 144

RDF Store Implementations 144

Retrieving Information in a Knowledgebase 146

Realizing the Semantics of OWL 147

Understanding Forward Chaining Inference 148

Understanding Backward Chaining Inference 152

Choosing the Right Inference Method 153

Common Frameworks and Components 153

RDF Store Implementations 154

Retrieval Components 156

Reasoning Engines 156

Knowledgebase Performance 157

Exploring the Profiles of OWL 158

OWL Full and OWL DL 159

The Profiles of OWL 160

OWL EL 160

OWL QL 161

OWL RL 162

Demonstrating OWL Inference 163

The Ontology 163

The Example Application 165

The Results 169

Performing No Inference 169

Performing RDFS Inference 170

Performing OWL Inference 171

Working with Ontologies 172

Decoupling the Knowledge Model from the Application 173

Sharing across Domain and Application Boundaries 174

What Is a Foundational Ontology? 175

Common Foundational Ontologies 177

BFO 177

Cyc and OpenCyc 178

DOLCE 179

SUMO 179

Dublin Core Metadata Initiative 179

FOAF 180

GeoRSS and OWL-Time 180

Finding Ontologies to Reuse or Extend 181

Choosing the Right Foundational Ontologies 183

Summary 184

Chapter 6 Discovering Information 185

Navigating the Semantic Web 186

Searching the Semantic Web 190

Querying the Semantic Web 192

Quickstart with SPARQL 192

Four Foundational Query Forms 196

SELECT Essentials 197

RDF Datasets, FROM and FROM NAMED 202

Query Modifiers 208

DISTINCT 209

REDUCED 210

ORDER BY 210

Data Streaming with OFFSET and LIMIT 211

Flexible Querying with FILTER and OPTIONAL 213

FILTER 213

OPTIONAL 215

UNION 219

CONSTRUCT Essentials 222

DESCRIBE Essentials 224

ASK Essentials 225

SPARQL Entailment 226

Unsupported Functionality 228

Data Modification 228

Subqueries 228

Aggregation 228

Summary 229

Chapter 7 Adding Rules 231

What Are Rules? 232

Reasons for Rules 232

No Support for Property Composition 232

Use of Built-ins 232

Ontological Mediation 233

Limiting Assumptions 233

Rule Languages 233

SWRL Essentials 234

The Abstract Syntax 235

The XML Concrete Syntax 237

var 238

imp 239

_rlab 239

_body 239

_head 240

classAtom 240

datarangeAtom 241

individualPropertyAtom 241

datavaluedPropertyAtom 242

sameIndividualAtom 242

differentIndividualsAtom 243

builtinAtom 243

The RDF Concrete Syntax 243

Built-ins 244

Examples 244

DL-Safe Rules 245

Ontological Mediation 252

Mapping Friends without Upsetting Any of Them 253

The Power of Rules 256

Jena Rules 257

Rule Interchange Format 259

Delving into the Details 260

The Future of RIF 260

Summary 261

Part Three Building Semantic Web Applications 263

Chapter 8 Applying a Programming Framework 265

Framing the Semantic Web 266

The Jena SemanticWeb Framework 269

Defining Jena Programming Concepts 269

Programming with Jena 273

Establishing the Jena Development Environment 276

Establishing the Knowledgebase: Setting Up the Model 276

Populating the Model with Semantic Web Data 279

Combining Semantic Web Data 282

Interrogating Semantic Web Data 283

Reasoning across Semantic Web Data 285

Exporting Semantic Web Data 290

Deallocating Semantic Web Data Resources 290

Managing Semantic Web Data 291

Getting Information Regarding Your Semantic Web Data 291

Generating Events Based on Semantic Web Data 292

Dealing with Concurrency and Your Semantic Web Data 293

Customizing the Jena Framework 295

Serializing Semantic Web Data 297

Common App Overview: FriendTracker 298

Summary 299

Chapter 9 Combining Information 301

Combining Information 303

Representing Information 303

Translating between Representations 304

Addressing the Challenges of Translation 305

Maintaining Fidelity 305

Tracking Provenance Information 305

Reversing the Process 306

Handling Varying Data 306

Managing Data Volume 306

Introducing the FriendTracker Data Sources 307

Facebook XML Web Service 307

Jabber Java Client 308

Upcoming.org XML Web Service 308

WordPress Relational Database 308

Exposing XML-Based Web Services as RDF 309

Introducing the Weather.gov XML Feed 310

Exposing XML Using XSL Transformations 311

Traversing XML Documents with XPath 313

Applying XSLT to a Simple Example 315

Processing XML and XSLT Programmatically 319

Applying XSLT to the Facebook Data Source 322

Weighing the Benefits and the Costs of XSLT 326

Exposing XML Using XML Bindings and Velocity 328

Generating Java Bindings for XML Data 329

Unmarshalling XML Data into Java 331

Introducing the Velocity Template Engine 333

Generating RDF with Velocity 336

Weighing the Benefits and the Costs 336

Exposing Relational Databases as RDF 337

Exposing a WordPress Blog Using D2RQ 338

Creating D2RQ Mappings for the WordPress Database 339

Wrapping the D2RQ Instance in a Jena Model 341

Querying the D2RQ Exposed WordPress Database 342

Weighing the Benefits and the Costs of D2RQ 345

Exposing Other Sources of Data 346

Exposing Jabber with a Custom Streaming RDF Writer 346

Exposing Java Objects Using Reflection 352

Applying the RDF Generator to the Weather.gov XML Feed 356

Applying the RDF Generator to the Upcoming.org XML Feed 358

Summary 359

Chapter 10 Aligning Information 361

Data Source, Domain, and Application Ontologies 361

Aligning Ontologies 362

Ontology Constructs 363

Translation via Rules 365

Explicit Translation 365

Ad Hoc Approaches to Translation 366

FriendTracker 366

Aligning Ontologies with OWL and SWRL 372

Aligning Ontologies with XSLT 376

Aligning Ontologies with Code 381

Aligning Simple Ontologies with RDFS 382

Record Linkage 385

Summary 388

Chapter 11 Sharing Information 389

Microformats 390

eRDF 392

RDFa 395

Supported Attributes 396

xmlns 396

rel 396

rev 398

content 398

href 399

src 399

about 399

property 399

resource 400

datatype 401

typeof 401

Blank Nodes 402

Language Support 403

Tools and Frameworks 404

RDF Transformational Tools 404

SPARQL Endpoints 404

Joseki Installation and Operation 405

xOperator 408

Installation and Operation 409

Example Query 410

FriendTracker in RDFa 411

Summary 417

Part Four Expanding Semantic Web Programming 419

Chapter 12 Developing and Using Semantic Services 421

Background 422

Discovery 424

Invocation 424

Negotiation 425

Error Handling 425

Monitoring 425

Composition 425

Implementing Semantic Services 426

Semantic Markup for Web Services 427

ServiceProfile 428

ServiceModel 428

ServiceGrounding 428

Web Service Modeling Ontology 429

Semantic Annotations for WSDL 432

SAWSDL Example 433

SAWSDL Tools 434

Summary 435

Chapter 13 Managing Space and Time 437

Space and Time in Software 437

Spatial Information 438

Temporal Information 440

Representing Spatiotemporal Data on the SemanticWeb 441

Spatial and Temporal Software with Jena 450

Working with Spatial Data 452

Example: Spatial Queries 453

Framing the Problem 453

Approach and Rationale 454

Components 454

Example: Transaction Time–Bounded Queries 461

Framing the Problem 461

Approach and Rationale 462

Components 462

Summary 465

Notes 465

Chapter 14 Semantic Web Patterns and Best Practices 467

Aggregating Disparate Data Sources 468

Exposing Data Sources as RDF 469

Bringing Data into the Domain Knowledge Model 470

Storing Information in the Knowledgebase 472

Initiating the Flow of Data 472

Annotating Unstructured Data 472

Annotation Management 474

Ontology Management 475

Unstructured Data Sources and the Client Application 476

Coordinating Semantic Services 478

Applying SemanticWeb Best Practices 480

Creating URIs 480

Making URIs Unique 480

Making URIs Consistent 481

Making URIs Resolvable 483

Specifying Units of Measurement 483

Unit-Specific Properties and Datatypes 484

Statement Reification 485

Value Containers 485

Representing N-ary Relationships 486

Managing Bad Data 487

Summary 487

Chapter 15 Moving Forward 489

Advancing Ontologies 491

Ontology Repositories and Registries 491

Linked Data 492

Versioning 493

Ontology Metrics 495

Advancing Integration 497

Semantic Pipes 497

Distributed Queries 498

Alignment 500

Advancing Reasoning 506

Rule Interchange Format (RIF) 506

Probabilistic Reasoning 507

Trust: Proof Markup Language 510

LarKC: The Large Knowledge Collider 512

Advancing Visualization 513

Summary 516

Appendix A RDF 519

Appendix B The OWL Web Ontology Language 525

Appendix C SWRL 533

Appendix D SPARQL 555

Appendix E Jena Reference Guide 567

Appendix F Installation Reference Guide 577

Index 585