1 What Is a Knowledge Graph? .............................................. 1
1.1 Introduction ............................................................. 1
1.2 Example 1: Academic Domain ......................................... 4
1.3 Example 2: Products and Companies .................................. 5
1.4 Example 3: Geopolitical Events........................................ 6
1.5 Conclusion .............................................................. 7
2 Information Extraction...................................................... 9
2.1 Introduction ............................................................. 9
2.2 Challenges of IE......................................................... 10
2.3 Scope of IE Tasks ....................................................... 11
2.3.1 Named Entity Recognition ..................................... 12
2.3.2 Relation Extraction ............................................. 22
2.3.3 Event Extraction ................................................ 24
2.3.4 Web IE .......................................................... 26
2.4 Evaluating IE Performance ............................................. 29
2.5 Summary ................................................................ 30
3 Entity Resolution............................................................. 33
3.1 Introduction ............................................................. 33
3.2 Challenges and Requirements .......................................... 34
3.3 Two-Step Framework ................................................... 38
3.3.1 Blocking......................................................... 39
3.3.2 Similarity ........................................................ 44
3.4 Measuring Performance ................................................ 47
3.4.1 Measuring Blocking Performance ............................. 48
3.4.2 Measuring Similarity Performance ............................ 50
3.5 Extending the Two-Step Workflow: A Brief Note ..................... 51
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3.6 Related Work: A Brief Review ......................................... 51
3.6.1 Automated ER Solutions ....................................... 52
3.6.2 Structural Heterogeneity........................................ 55
3.6.3 Blocking Without Supervision: Where Do We Stand?........ 56
3.7 Summary ................................................................ 57
4 Advanced Topic: Knowledge Graph Completion ........................ 59
4.1 Introduction ............................................................. 59
4.2 Knowledge Graph Embeddings ........................................ 61
4.2.1 TransE ........................................................... 63
4.2.2 TransE Extensions and Alternatives ........................... 64
4.2.3 Limitations and Alternatives ................................... 66
4.2.4 Research Frontiers and Recent Work .......................... 66
4.2.5 Applications of KGEs .......................................... 72
4.3 Summary ................................................................ 74
5 Ecosystems.................................................................... 75
5.1 Introduction ............................................................. 75
5.2 Web of Linked Data ..................................................... 75
5.2.1 Linked Data Principles ......................................... 77
5.2.2 Technology Stack ............................................... 78
5.2.3 Linking Open Data ............................................. 79
5.2.4 Example: DBpedia.............................................. 80
5.3 Google Knowledge Vault ............................................... 82
5.4 Schema.org .............................................................. 84
5.5 Where is the Future Going? ............................................ 86
Glossary ........................................................................... 89
References......................................................................... 93
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