1. Semantic Web for the Working Ontologist Dean Allemang Jim Hendler SNU IDB laboratory Last modified, 2014.11.03

2. Semantic Web for the Working OntologistDean Allemang, Jim Hendler Chapter 6 RDF and Inferencing ■ 1. Inference in the Semantic Web 1.1 SPARQL and inference 1.2 Virtues of Inference-Based Semantics ■ 2. Where are the Smarts? 2.1 Asserted Triples versus Inferred Triples ■ 3. When Does Inferencing Happen? 3.1 Inferencing as specification 2/16

3. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Inference in the Semantic Web [1/6] chamois search shirts category results nothing chamois search Henleys category results 3/16

4. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Inference in the Semantic Web [2/6] ■ Solution leverage the power of the query ▶ E.g. “Show me all items in category ‘Shirts’, or in any subcategory of ‘Shi rts’, or any sub-subcategory of ‘Shirts’, and so on” 4/16

5. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Inference in the Semantic Web [3/6] ■ To make data seem more connected and integrated Add relationships into data “shirts” is a broader term than “Henleys” “Henleys” is a subclass of the “Shirts” 5/16

6. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Inference in the Semantic Web [4/6] ■ subClassOf “B is subClassOf C” ▶ “Every member of class B is also a member of class C” ▶ This specification is based on the notion of inference − “x is a member B” → “x is a member of C” ■ The pattern for the subClassOf in RDFS IF ? A rdfs:subClassOf ?B AND ?x rdf: type ?A THEN ?x rdf: type ?B type propagation 6/16

7. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Inference in the Semantic Web [5/6] ■ Virtues of Inference-Based Semantics Informal thesaurus setting ▶ Needs discussions and design decisions Inference-based system ▶ Defined by the interaction of the basic inference patterns − “If A is subClassOf B and A is also subClassOf C, then any individual x that is a member of A will be a member of B and C” 7/16

8. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 1. Inference in the Semantic Web [6/6] ■ RDF Store shop:Henleys rdfs:subClassOf shop:Shirts. shop:ChamoisHenley rdf:type shop:Henleys. ■ Query SELECT ?item WHERE {?x rdf:type shop:Shirts. } ■ Plain RDF -> No match ■ RDFS inferencing query engine -> Shop:ChamoisHenley 8/15

9. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 2. Where are the Smarts? [1/4] ■ Triples = asserted triples + inferred triples ■ Asserted Triples vs Inferred Triples Asserted triples - asserted in the original RDF store Inferred triples - additional triples that are inferred by inference rules No logical distinction 9/16

10. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 2. Where are the Smarts? [2/4] ■ Example shop:MensWear shop:Oxfords shop:Shirts shop:Henleys shop:Tshirts shop:ChamoisHenley shop:ClassicOxford rdfs:subClassOf rdf:type 10/16

11. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 2. Where are the Smarts? [3/4] ■ Example shop:Henleys rdfs:subClassOf shop:Shirts. shop:Shirts rdfs:subClassOf shop:MensWear. shop:Blouses rdfs:subClassOf shop:WomensWear. shop:Oxfords rdfs:subClassOf shop:Shirts. shop:Tshirts rdfs:subClassOf shop:Shirts. shop:ChamoisHenley rdfs:type shop:Henleys. shop:ClassicOxford rdfs:type shop:Oxfords. shop:ClassicOxford rdfs:type shop:Shirts. shop:BikerT rdfs:type shop:TShirts. shop:BikerT rdfs:type shop:Menswear. shop:ChamoisHenley rdf:type shop:Shirts. shop:ChamoisHenley rdf:type shop:MensWear. shop:ClassicOxford rdf:type shop:Shirts. shop:ClassicOxford rdf:type shop:MensWear. shop:BikerT rdf:type shop:Shirts. shop:BikerT rdf:type shop:MensWear. inference 11/16

12. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 2. Where are the Smarts? [4/4] ■ Example shop:MensWear shop:Oxfords shop:Shirts shop:Henleys shop:Tshirts shop:ChamoisHenley shop:ClassicOxford Inferred triples 12/16

13. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3. When does Inferencing happen? [1/2] ■ When does Inferencing happen? The simplest approach ▶ Quite simple to describe and implement ▶ Risks an explosion of triples in the triple store Store all triples in a single store Any inferred triples are inserted into the store Asserted & Inferred inferencing 13/16

14. Semantic Web for the Working OntologistDean Allemang, Jim Hendler 3. When does Inferencing happen? [2/2] ■ When does inferencing happen? Another approach ▶ Risks duplicating inference work ▶ Parsimonious in terms of persistent storage Never store any inferred triples Inferencing is done in response to queries only Asserted inferencing query 14/16

15. Thank you