An Introduction to SPARQL and Queries over Linked Data · Olaf Hartig - ICWE 2012 Tutorial "An...

ICWE 2012 Tutorial

An Introduction to SPARQL and Queries over Linked Data

● ● ●

Hands-on Exercises

Olaf Hartighttp://olafhartig.de/foaf.rdf#olaf

@olafhartig

Database and Information Systems Research GroupHumboldt-Universität zu Berlin

Olaf Hartig - ICWE 2012 Tutorial "An Introduction to SPARQL and Queries over Linked Data" - Hands-on Exercises 2

Exercise 1

Ask for the title (property: 'dc:title') of each workshop (class: 'swc:WorkshopEvent').

Exercise 1

PREFIX swc: <http://data.semanticweb.org/ns/swc/ontology#>

PREFIX dc: <http://purl.org/dc/elements/1.1/>

SELECT ?wt WHERE {

?w a swc:WorkshopEvent ;

dc:title ?wt .

SELECT ?wt WHERE {

dc:title ?wt .

Ask for the title (property: 'dc:title') of each workshop (class: 'swc:WorkshopEvent').

Exercise 2

Ask for an ordered list of the subjects (property:'dc:subject') of all workshops; each subject must not appear more than once.

Exercise 2

SELECT DISTINCT ?s WHERE {

dc:subject ?s .

ORDER By ?s

SELECT DISTINCT ?s WHERE {

dc:subject ?s .

ORDER By ?s

Ask for an ordered list of the subjects (property:'dc:subject') of all workshops; each subject must not appear more than once.

Exercise 3

Ask for the title of workshops that have "Linked Data" as their subject.

Exercise 3

SELECT ?wt WHERE {

dc:title ?wt ;

dc:subject "Linked Data" .

SELECT ?wt WHERE {

dc:title ?wt ;

dc:subject "Linked Data" .

Ask for the title of workshops that have "Linked Data" as their subject.

Exercise 4

Does the result for the previous query contain the USEWOD workshop? Investigate why (using SPARQL queries similar to the previous ones) and adjust the query so that the USEWOD workshop becomes part of the result.

Exercise 4

SELECT ?wt WHERE {

dc:title ?wt .

{ ?w dc:subject "Linked Data" }

{ ?w dc:subject "linked data" }

SELECT ?wt WHERE {

dc:title ?wt .

{ ?w dc:subject "Linked Data" }

{ ?w dc:subject "linked data" }

Exercise 4 (Alternative)

SELECT ?wt WHERE {

dc:title ?wt ;

dc:subject ?ws .

FILTER regex( ?ws, "linked data", "i" )

SELECT ?wt WHERE {

dc:title ?wt ;

dc:subject ?ws .

FILTER regex( ?ws, "linked data", "i" )

Exercise 5

Each workshop took place in a particular location (property: 'swc:hasLocation'). Ask for the label (property: 'rdfs:label') of these locations; pair them with the title of the corresponding workshop.

Exercise 5

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>

SELECT ?wt ?ll WHERE {

dc:title ?wt ;

swc:hasLocation ?l .

?l rdfs:label ?ll .

SELECT ?wt ?ll WHERE {

dc:title ?wt ;

?l rdfs:label ?ll .

Each workshop took place in a particular location (property: 'swc:hasLocation'). Ask for the label (property: 'rdfs:label') of these locations; pair them with the title of the corresponding workshop.

Exercise 6

Ask for the URI of any event that took place in the same location as the USEWOD workshop; the USEWOD workshop must not be listed

(URI: 'http://data.semanticweb.org/workshop/usewod/2012')

Exercise 6

SELECT ?e WHERE {

<http://data.semanticweb.org/workshop/usewod/2012>

?e swc:hasLocation ?l .

FILTER ( ?e != <http://data.semanticweb.org/workshop/usewod/2012> )

SELECT ?e WHERE {

?e swc:hasLocation ?l .

FILTER ( ?e != <http://data.semanticweb.org/workshop/usewod/2012> )

Ask for the URI of any event that took place in the same location as the USEWOD workshop; the USEWOD workshop must not be listed

(URI: 'http://data.semanticweb.org/workshop/usewod/2012')

Exercise 7

Ask for events that took place before the USEWOD workshop, in the same location as the USEWOD workshop. (Hint: events have properties 'ical:dtstart' and 'ical:dtend')

Exercise 7

PREFIX ical: <http://www.w3.org/2002/12/cal/icaltzd#>

SELECT ?e WHERE {

swc:hasLocation ?l ;

ical:dtstart ?dt1 .

?e swc:hasLocation ?l ;

ical:dtend ?dt2 .

FILTER (?dt2 < ?dt1)

PREFIX ical: <http://www.w3.org/2002/12/cal/icaltzd#>

SELECT ?e WHERE {

swc:hasLocation ?l ;

ical:dtstart ?dt1 .

ical:dtend ?dt2 .

FILTER (?dt2 < ?dt1)

Ask for events that took place before the USEWOD workshop, in the same location as the USEWOD workshop. (Hint: events have properties 'ical:dtstart' and 'ical:dtend')

Exercise 8

While all events that took place in the same location as the USEWOD workshop have a label (property: 'rdfs:label'), only some of them have a title (property: 'dc:title'). List these labels and if the corresponding event also has a title, then show this title in addition to the label. (Hint: use OPTIONAL)

Exercise 8

SELECT ?el ?et WHERE {

rdfs:label ?el .

OPTIONAL { ?e dc:title ?et }

rdfs:label ?el .

OPTIONAL { ?e dc:title ?et }

While all events that took place in the same location as the USEWOD workshop have a label (property: 'rdfs:label'), only some of them have a title (property: 'dc:title'). List these labels and if the corresponding event also has a title, then show this title in addition to the label. (Hint: use OPTIONAL)

Exercise 9

Adjust the previous query such that it only lists the labels of those events that do not have a title (and that took place in the same location as the USEWOD workshop). (Hint: use the negation by failure pattern)

Exercise 9

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX swc: <http://data.semanticweb.org/ns/swc/ontology#>

<http://data.semanticweb.org/workshop/usewod/2012> swc:hasLocation ?l .

rdfs:label ?el .

OPTIONAL { ?e dc:title ?et . }

FILTER ( ! BOUND(?et) )

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX swc: <http://data.semanticweb.org/ns/swc/ontology#>

<http://data.semanticweb.org/workshop/usewod/2012> swc:hasLocation ?l .

rdfs:label ?el .

OPTIONAL { ?e dc:title ?et . }

FILTER ( ! BOUND(?et) )

Adjust the previous query such that it only lists the labels of those events that do not have a title (and that took place in the same location as the USEWOD workshop). (Hint: use the negation by failure pattern)

Exercise 10

Adjust the previous query such that it lists the labels of those events that do not have a title and it lists the title of those events that have a title (and a label); in both cases use the same variable for the output, that is, the query result should consist of a single column only.

Exercise 10

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>PREFIX swc: <http://data.semanticweb.org/ns/swc/ontology#>PREFIX dc: <http://purl.org/dc/elements/1.1/>

SELECT ?el WHERE {

<http://data.semanticweb.org/workshop/usewod/2012> swc:hasLocation ?l . ?e swc:hasLocation ?l .

{ ?e rdfs:label ?el . OPTIONAL { ?e dc:title ?et } FILTER ( ! BOUND(?et) )

} UNION { ?e dc:title ?el }

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>PREFIX swc: <http://data.semanticweb.org/ns/swc/ontology#>PREFIX dc: <http://purl.org/dc/elements/1.1/>

SELECT ?el WHERE {

<http://data.semanticweb.org/workshop/usewod/2012> swc:hasLocation ?l . ?e swc:hasLocation ?l .

{ ?e rdfs:label ?el . OPTIONAL { ?e dc:title ?et } FILTER ( ! BOUND(?et) )

} UNION { ?e dc:title ?el }

Adjust the previous query such that it lists the labels of those events that do not have a title and it lists the title of those events that have a title (and a label); in both cases use the same variable for the output, that is, the query result should consist of a single column only.

These slides have been created byOlaf Hartig

http://olafhartig.de

This work is licensed under aCreative Commons Attribution-Share Alike 3.0 License

(http://creativecommons.org/licenses/by-sa/3.0/)

An Introduction to SPARQL and Queries over Linked Data · Olaf Hartig - ICWE 2012 Tutorial "An...

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