There are 4 SPARQL query forms: SELECT, ASK, CONSTRUCT, and DESCRIBE. Each form serves a different purpose. SELECT returns variable bindings and is equivalent to an SQL SELECT query. ASK returns a boolean for whether a pattern matches or not. CONSTRUCT returns an RDF graph constructed from templates. DESCRIBE returns an RDF graph that describes resources found. Beyond their basic uses, the forms can be used for tasks like indexing, transformation, validation, and prototyping user interfaces.

1. SPARQL Query Forms Leigh Dodds, Oxford SWIG, March 2008 Photo Credit: Glen Bowman

2. Why are there 4 SPARQL Query Forms? SPARQL Use Cases doesn’t help very much…

3. …neither does the SPARQL specification SELECT Returns all, or a subset of, the variables bound in a query pattern match. CONSTRUCT Returns an RDF graph constructed by substituting variables in a set of triple templates. ASK Returns a boolean indicating whether a query pattern matches or not. DESCRIBE Returns an RDF graph that describes the resources found.

4. What are they for?

5. SELECT Equivalent to SQL SELECT Returns a nice, regular table

6. SELECT PREFIX table: <http://www.daml.org/2003/01/periodictable/PeriodicTable#> SELECT ?name ?weight WHERE { ?element table:name ?name; table:atomicWeight ?weight. } ORDER BY DESC(?weight) LIMIT 10

7. ASK Returns a true/false value Is there data that looks like this ? Do you have any information about that ?

8. ASK PREFIX foaf: <http://xmlns.com/foaf/0.1/> ASK WHERE { ?person a foaf:Person ; foaf:mbox <mailto:leigh@ldodds.com>. } (SPARQL equivalent of a vanity search!)

9. CONSTRUCT Returns an RDF graph Extract a specific subset of the queried data I want this , this , and this

10. CONSTRUCT PREFIX foaf: <http://xmlns.com/foaf/0.1/> CONSTRUCT { ?friend a foaf:Person; foaf:name ?name; foaf:homepage ?home. } WHERE { ?person foaf:mbox <mailto:leigh@ldodds.com>; foaf:knows ?friend. ?friend foaf:name ?name; foaf:homepage ?home. }

11. DESCRIBE Returns an RDF graph Tell me about this or things that look like this … but you decide what’s relevant

12. DESCRIBE PREFIX foaf: <http://xmlns.com/foaf/0.1/> DESCRIBE ?friend WHERE { ?person foaf:mbox “mailto:leigh@ldodds.com”; foaf:knows ?friend. }

13. Applied Uses Beyond the basics

14. DESCRIBE for Prototyping DESCRIBE <http://example.org/someResource> Quickly assembling UIs Web APIs

15. SELECT for Indexing Building an ordering over some data ORDER BY, LIMIT

16. CONSTRUCT for Transformation … and also simple inferencing CONSTRUCT could be the XSLT of RDF Currently limited by lack of expressions in CONSTRUCT triple templates

17. CONSTRUCT for Transformation PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX ex: <http://www.example.org/blogger/> CONSTRUCT { ?person a ex:Blogger. } WHERE { ?person foaf:weblog ?blog. }

18. SPARQL for Validation XSLT can be used for XML Validation (Schematron) SPARQL can be used for RDF Validation

19. Validation – ASK * ASK WHERE { #triple patterns that you don’t want to find } *Source: Talis Platform Field Predicate Map Validation

20. Validation – CONSTRUCT * CONSTRUCT { #some error message or data } WHERE { #triple patterns that you don’t want to find } *Source: Alistair Miles, Schemarama 2 Jena 2 Validation Support

21. In Combination?

22. The ADC Pattern ASK – DESCRIBE – CONSTRUCT Probe endpoint Grab default view of data Refine data extraction and/or apply transformation

23. Questions?