programming_the_semantic_web.pdf

reword ................................................................... xi Preface .................................................................... xiii Part I. Semantic Data 1.Why Semantics? ........................................................ 3 Data Integration Across the Web 4 Traditional Data-Modeling Methods 5 Tabular Data 6 Relational Data 7 Evolving and Refactoring Schemas 9 Very Complicated Schemas 11 Getting It Right the First Time 12 Semantic Relationships 14 Metadata Is Data 16 Building for the Unexpected 16 “Perpetual Beta” 17 2.Expressing Meaning .................................................... 19 An Example: Movie Data 21 Building a Simple Triplestore 23 Indexes 23 The add and remove Methods 24 Querying 25 Merging Graphs 26 Adding and Querying Movie Data 28 Other Examples 29 Places 29 Celebrities 31 Business 33 v Download at Boykma.Com 3.Using Semantic Data ................................................... 37 A Simple Query Language 37 Variable Binding 38 Implementing a Query Language 40 Feed-Forward Inference 43 Inferring New Triples 43 Geocoding 45 Chains of Rules 47 A Word About “Artificial Intelligence” 50 Searching for Connections 50 Six Degrees of Kevin Bacon 51 Shared Keys and Overlapping Graphs 53 Example: Joining the Business and Places Graphs 53 Querying the Joined Graph 54 Basic Graph Visualization 55 Graphviz 55 Displaying Sets of Triples 56 Displaying Query Results 57 Semantic Data Is Flexible 59 Part II. Standards and Sources 4.Just Enough RDF ....................................................... 63 What Is RDF? 63 The RDF Data Model 64 URIs As Strong Keys 64 Resources 65 Blank Nodes 66 Literal Values 68 RDF Serialization Formats 68 A Graph of Friends 69 N-Triples 70 N3 72 RDF/XML 73 RDFa 76 Introducing RDFLib 80 Persistence with RDFLib 83 SPARQL 84 SELECT Query Form 86 OPTIONAL and FILTER Constraints 87 Multiple Graph Patterns 89 CONSTRUCT Query Form 91 vi|Table of Contents Download at Boykma.Com ASK and DESCRIBE Query Forms 91 SPARQL Queries in RDFLib 92 Useful Query Modifiers 94 5.Sources of Semantic Data ............................................... 97 Friend of a Friend (FOAF) 97 Graph Analysis of a Social Network 101 Linked Data 105 The Cloud of Data 106 Are You Your FOAF file? 107 Consuming Linked Data 110 Freebase 116 An Identity Database 117 RDF Interface 118 Freebase Schema 119 MQL Interface 121 Using the metaweb.py Library 123 Interacting with Humans 125 6.What Do You Mean, “Ontology”? ........................................ 127 What Is It Good For? 127 A Contract for Meaning 128 Models Are Data 128 An Introduction to Data Modeling 129 Classes and Properties 129 Modeling Films 132 Reifying Relationships 134 Just Enough OWL 135 Using Protégé 140 Creating a New Ontology 140 Editing an Ontology 141 Just a Bit More OWL 145 Functional and Inverse Functional Properties 146 Inverse Properties 146 Disjoint Classes 146 Keepin’ It Real 148 Some Other Ontologies 148 Describing FOAF 148 A Beer Ontology 149 This Is Not My Beautiful Relational Schema! 152 7.Publishing Semantic Data .............................................. 155 Embedding Semantics 155 Table of Contents|vii Download at Boykma.Com Microformats 156 RDFa 158 Yahoo! SearchMonkey 160 Google’s Rich Snippets 161 Dealing with Legacy Data 162 Internet Video Archive 162 Tables and Spreadsheets 167 Legacy Relational Data 169 RDFLib to Linked Data 172 Part III. Putting It into Practice 8.Overview of Toolkits ................................................... 183 Sesame 183 Using the Sesame Java API 184 RDFS Inferencing in Sesame 193 A Servlet Container for the Sesame Server 196 Installing the Sesame Web Application 196 The Workbench 197 Adding Data 199 SPARQL Queries 200 REST API 202 Other RDF Stores 203 Jena (Open Source) 204 Redland (Open Source) 204 Mulgara (Open Source) 204 OpenLink Virtuoso (Commercial and Open Source) 204 Franz AllegroGraph (Commercial) 205 Oracle (Commercial) 205 SIMILE/Exhibit 205 A Simple Exhibit Page 206 Searching, Filtering, and Prettier Views 209 Linking Up to Sesame 211 Timelines 212 9.Introspecting Objects from Data ......................................... 215 RDFObject Examples 215 RDFObject Framework 217 How RDFObject Works 225 10.Tying It All Together ................................................... 227 A Job Listing Application 227 viii|Table of Contents Download at Boykma.Com Application Requirements 228 Job Listing Data 228 Converting to RDF 228 Loading the Data into Sesame 231 Serving the Website 232 CherryPy 232 Mako Page Templates 233 A Generic Viewer 234 Getting Data from Sesame 236 The Generic Template 236 Getting Company Data 237 Crunchbase 238 Yahoo! Finance 241 Reconciling Freebase Connections 243 Specialized Views 244 Publishing for Others 248 RDFa 248 RDF/XML 250 Expanding the Data 251 Locations 251 Geography, Economy, Demography 252 Sophisticated Queries 253 Visualizing the Job Data 255 Further Expansion 258 Part IV. Epilogue 11.The Giant Global Graph ................................................ 261 Vision, Hype, and Reality 262 Participating in the Global Graph Community 264 Releasing Data into the Commons 265 License Considerations 266 The Data Cycle 267 Bracing for Continuous Change 268 Index ..................................................................... 271