SPARQL In-Class Shared Exercise

1. SPARQL In-Class Shared Exercise

2. Pop Quiz • If you have a large knowledge store, why should you not issue: SELECT ?s ?p ?o WHERE { ?s ?p ?o } Ans: It returns the entire knowledge store (i.e. all triples)

3. Answer: 3 Pop Quiz 1. How many triples? <rdf:Description rdf:about="http://www.example.org/index.html"> <exterms:creation-date>August 16, 1999</exterms:creation-date> <dc:language>en</dc:language> <dc:creator rdf:resource="http://www.example.org/staffid/85740"/> </rdf:Description>

4. Pop Quiz 2. What is the query result? What is the query result: PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX ex: <http://www.example.orgterms/> SELECT ?o WHERE { ?s dc:creator ?p. ?s ex:creation-date ?o } Answer: 3 August 16, 1999

5. Pop Quiz 3. What is the query result? What is the query result: PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX ex: <http://www.example.orgterms/> SELECT ?o WHERE { ?s dc:creator ?p. ?s ex:creation-date ?o. ?p dc:language “en” } Answer: 3 <empty>

6. Ans: 7 Pop Quiz • 1. How many triples? • <rdf:Description rdf:about="http://example.org/courses/6.001"> • <s:students> • <rdf:Bag> • <rdf:li rdf:resource="http://example.org/students/Amy"/> • <rdf:li rdf:resource="http://example.org/students/Mohamed"/> • <rdf:li rdf:resource="http://example.org/students/Johann"/> • <rdf:li rdf:resource="http://example.org/students/Maria"/> • <rdf:li rdf:resource="http://example.org/students/Phuong"/> • </rdf:Bag> • </s:students> • </rdf:Description>

7. Pop Quiz 2. What is the query result? What is the query result: PREFIX ex: <http://example.org/students/> PREFIX exv: <http://example.org/students/vocab#> PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> SELECT ?o WHERE { ?s a rdf:Bag. ?s2 exv:students ?s. { ?s rdf:_1 ?o. } UNION { ?s rdf:_2 ?o. } } http://example.org/students/Amy http://example.org/students/Mohamed

8. http://example.org/students/Johann Returns the last of every list in the knowledge store - > Not generally useful. Pop Quiz 2. What is the query result? What is the query result: PREFIX ex: <http://example.org/students/> PREFIX exv: <http://example.org/students/vocab#> PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> SELECT ?o WHERE { (?o2) rdf:first ?o. }

9. http://example.org/students/Mohamed Returns the next to last of every list in the knowledge store. Pop Quiz 3. What is the query result? What is the query result: PREFIX ex: <http://example.org/students/> PREFIX exv: <http://example.org/students/vocab#> PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> SELECT ?o WHERE { ?s2 rdf:rest (?o2); rdf:first ?o. }

10. Exercise Preliminaries • Have Gruff installed and working (item 3 of Lab 2) • Get example rdf files (on eLearning Lecture 5 directory)

11. Start-up (Together) • Start GRUFF • Create a new triple store • Put somewhere convenient • Name it funtoday • Use default estimate of size • Load rdf files • Load one at a time • ericMiller.rdf • smallSet.rdf • Display Both Graphs • Add->Display all triples

12. First SPARQL • Switch to gruff Query view • View->Query view • Create a query that returns all triples (using the SELECT construct) • Run it - How many triples? • Shows at bottom just after query runs • Hit ‘Do Query’ again SELECT ?s ?p ?o WHERE { ?s ?p ?o. }

13. Sub-selection • Return the objects and properties for ‘…Me’ • Windows help: Shift+LeftClick, then Ctrl-C can copy a field (Ctrl-V to paste) (See View menu for shortcuts) • Run it - How many triples? SELECT ?p ?o WHERE { <http://www.w3.org/People/EM/contact#me> ?p ?o }

14. PREFIX • Add a prefix statement for …Me • Call the prefix em • Change the where clause to use the prefix • Run the query • How many triples • Same answer as before? PREFIX em: <http://www.w3.org/People/EM/contact#> SELECT ?p ?o WHERE { em:me ?p ?o }

15. Classes Used • Change the query to find all the classes being used in the knowledge store • Did the query get to unique answers or was it just our store? SELECT ?o WHERE { ?s a ?o } or rdf:type for ‘a’ NOTE: rdf is predefined for you. Answer: Just our store. Can use DISTINCT SELECT DISTINCT ?o WHERE { ?s a ?o }

16. More Data • Load more rdf files • BagExample.rdf • collectionExample.rdf • Display all nodes • Arrange 6.001 and 6.002, each as top of a path (with some shared resources) • Make note of the types of nodes, which have class types, and names of property types. • Especially that bag uses a type, list doesn’t

17. First Bag Item • Write select query to return the ‘first’ bag item of class 6.001 down the students path. • Use the prefixes: • PREFIX ex: <http://example.org/courses/> • PREFIX exv: <http://example.org/students/vocab#> PREFIX ex: <http://example.org/courses/> PREFIX exv: <http://example.org/students/vocab#> SELECT ?o WHERE { ex:6.001 exv:students ?bn. ?bn rdf:_1 ?o}

18. Bag Iteration • How do you change the query to get the next bag item? Answer: Change _1 to _2 -similar for all others until no return PREFIX ex: <http://example.org/courses/> PREFIX exv: <http://example.org/students/vocab#> SELECT ?o WHERE { ex:6.001 exv:students ?bn. ?bn rdf:_2 ?o}

19. First List Item • Change the query to return the ‘first’ list item of class 6.002 down the students path. • Use the prefixes: • PREFIX ex: <http://example.org/courses/> • PREFIX exv: <http://example.org/students/vocab#> PREFIX ex: <http://example.org/courses/> PREFIX exv: <http://example.org/students/vocab#> SELECT ?o WHERE { ex:6.002 exv:students ?bn. ?bn rdf:first ?o }

20. List Iteration • How do you change the query to get the next list item? Answer: Extend the chain further down -You cannot use the blank node identifier in a new sparql query (per the specification). -You have to extend the chain more for each -rdf:nil return indicates end of list -this can be a fine structure for non-SPARQL graph access PREFIX ex: <http://example.org/courses/> PREFIX exv: <http://example.org/students/vocab#> SELECT ?o WHERE { ex:6.002 exv:students ?bn. ?bn rdf:rest ?bn2. ?bn2 rdf:first ?o. } Last Gruff Example – remainder are verbal exercises

21. Explicit Inference • My ontology says that zebra is a subclass of mammal. Modify the query below to implement the inference. SELECT ?o WHERE { ?s1 a mammal. ?s1 someProperty ?o } SELECT ?o WHERE { {?s1 a mammal} UNION {?s1 a zebra} ?s1 someProperty ?o } The Lesson: SPARQL can be automatically converted to accommodate subClassOf in an ontology.

22. Explicit Inference • My ontology says that endsAtDateTime is a subproperty of endsAt. Modify the query below to implement the inference. SELECT ?o WHERE { ?s1 a event. ?s1 endsAt ?o } SELECT ?o WHERE { ?s1 a event. {?s1 endsAt ?o} UNION {?s1 endsAtDateTime ?o} } The Lesson: SPARQL can be automatically converted to accommodate subPropertyOf in an ontology.

23. Explicit Inference • My ontology says the domain of property ‘teaches’ is class ‘person’. Modify the query below to implement the inference. SELECT ?o WHERE { ?s1 a person. ?s1 someProperty ?o } SELECT ?o WHERE { {?s1 a person} UNION {?s1 teaches ?junk} ?s1 someProperty ?o } The Lesson: SPARQL can be automatically converted to accommodate domain and range in an ontology.

24. Explicit Inference • WARNING • Implementation of inference of complicated ontologies in SPARQL queries can easily make SPARQL queries unreasonably long to execute • There are limits to how much inference can be performed in a SPARQL SELECT • It cannot perform inference over classes, properties, etc. found during the query (i.e. found as a variable like ?p)