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

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

…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.

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.

What are they for?

SELECT Equivalent to SQL SELECT Returns a nice, regular table

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

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

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!)

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

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. }

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

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

Applied Uses Beyond the basics

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

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

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

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. }

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

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

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

In Combination?

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

Questions?