📓 pages/SPARQL training course.md by @sparql ☆

All important points from the training course, collected for quick reference. See also [[Tutorial]]s.
SPARQL Interactions
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- See [[SPARQL Tools]]
- See [[Querying with curl]]
Two triple patterns, same subject
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- ```
SELECT ?country ?capital ?population 

WHERE {
?country dbo:capital ?capital .
?country dbp:populationTotal ?population .
} 
```
  #Query #DBpedia
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Making another step in the graph

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SELECT ?country ?population ?capital 

WHERE {
?country a dbo:Country .
?country dbp:populationTotal ?population . 
?country dbo:capital ?capital_URI .
                     ?capital_URI   rdfs:label ?capital .
}

#Query #DBpedia

{:height 373, :width 646}

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PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX skosxl: <http://www.w3.org/2008/05/skos-xl#>

SELECT * 

WHERE {
    
    ?s skosxl:prefLabel ?Label_URI .
    ?Label_URI skosxl:literalForm ?label .

    FILTER (LANG(?label) = "es")
}

#VocBench #Query

Three patterns and two filters

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SELECT ?country ?population ?capital 

WHERE {
?country a dbo:Country; 
            dbo:populationTotal ?population; 
            dbo:capital ?capital_URI .
?capital_URI rdfs:label ?capital .

FILTER ( LANG(?capital) = "en" )
FILTER ( xsd:int(?population) > 10000000 )
} 

ORDER BY DESC(?population)

#Query #DBpedia #FILTER #LANG

Counting and Binding

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SELECT (COUNT (?work_of_Agatha_Christie) AS ?Number_of_AC_works)

{?work_of_Agatha_Christie dbo:author dbr:Agatha_Christie }

#Query #COUNT

See [[Function/Aggregate Function]]

Functions on dates and times
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- [NOW]
- [YEAR]
- [MONTH]
- [DAY]
- [HOURS]
- [MINUTES]
- [SECONDS]
- [[Example]] collapsed:: true
  - ```
  SELECT (MONTH(NOW()) AS ?currentMonth) { }
```
  #Query

Filtering resources with the same namespace

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Find all [[SKOS]] properties in use

SELECT DISTINCT ?property
WHERE {
    ?s ?property ?o .
    FILTER (STRSTARTS(STR(?property), "http://www.w3.org/2004/02/skos/core#" ))
}

#Query #STRSTARTS

Find all classes of things that have author DBpedia

SELECT DISTINCT ?class
WHERE {
  ?work dbo:author ?author . 
  ?work a ?class .
FILTER (STRSTARTS(STR(?class),"http://dbpedia.org/ontology/" ))  
}

#Query #STRSTARTS #DBpedia

Negation
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- NOT EXISTS - Testing for absence of a pattern (recommended in most cases)
- MINUS - Removing possible solutions
- !BOUND - Not bound (produces the same results as NOT EXISTS but works also for SPARQL 1.0)
- #+BEGIN_IMPORTANT NOT EXISTS and MINUS have different logic and may produce different results on the same dataset. #+END_IMPORTANT
- ```
SELECT ?work 
WHERE {
  ?work a dbo:Artwork .
  ?work dbo:museum dbr:Louvre .

  FILTER NOT EXISTS {?work dbo:author ?artist .}
}
```
  #Query #FILTER #[[NOT EXISTS]]

Optional results

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SELECT ?work ?artist
WHERE {
  ?work a dbo:Artwork .
  ?work dbo:museum dbr:Louvre .
  
  OPTIONAL {?work dbo:author ?artist .}
}
ORDER BY ?artist
}

#Query #OPTIONAL #[[ORDER BY]]

Combining results

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PREFIX dbr: <http://dbpedia.org/resource/>
PREFIX dbo: <http://dbpedia.org/ontology/>

SELECT ?Influenced

WHERE { 
{ ?Influenced dbo:influencedBy  dbr:Ludwig_Wittgenstein.} 

  UNION 

{ dbr:Ludwig_Wittgenstein dbo:influenced ?Influenced .} 
}

#Query #UNION

Search for string patterns

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SELECT DISTINCT ?MusicalWork ?Artist

WHERE {
?MusicalWorkURI a dbo:MusicalWork ;
               rdfs:label ?MusicalWork ;
               dbo:artist ?ArtistURI .

?ArtistURI rdfs:label ?Artist .

FILTER (lang(?MusicalWork) = "en")
FILTER (lang(?Artist) = "en")
FILTER REGEX (?MusicalWork, "broken", "i")
}
ORDER BY ?MusicalWork

#Query #REGEX #FILTER #LANG #[[ORDER BY]]

Assembling strings

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PREFIX cdm: <http://publications.europa.eu/ontology/cdm#>

SELECT ?reg (IRI(CONCAT(STR(?eli),"/eng/pdf")) AS ?pdf_URL)

{
  ?reg cdm:resource_legal_eli ?eli .
}

LIMIT 1000

#Query #IRI #CONCAT #Cellar

Property paths

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[[Syntax]]

#Inverse Path:
    ^:property #Inverse path (object to subject)
#Sequence Path:
    :property1/:property2  #A sequence path of :property1 followed by :property2
#Alternative Path:
    :property1|:property2  #:property1 or property2 (all possibilities are tried)
#Zero Or More:
    :property*  #A path that connects the subject and object of the path by zero or more matches of :property
#One Or More:
    :property+  #A path that connects the subject and object of the path by one or more matches of :property
#Zero Or One Path:
    :property?  #A path that connects the subject and object of the path by zero or one matches of :property

Property paths from the SPARQL 1.1 spec

[[Example]] collapsed:: true

SELECT (COUNT (DISTINCT ?child) AS ?Number_of_children)

{
?MS a dbo:Country; 
    dct:subject dbc:Member_states_of_the_European_Union ;
    dbp:leaderName ?leader . 

?leader dbo:child|^dbo:parent  ?child.

#Works the same as 
#  {?leader dbo:child ?child.}
#  UNION
#  {?child dbo:parent ?leader}
}

#Query #| #^ #UNION

SELECT
(COUNT (DISTINCT ?Influencer) AS ?Num_Influencer) 
(COUNT (DISTINCT ?Influenced) AS ?Num_Influenced) 

WHERE {

     {dbr:Ludwig_Wittgenstein dbo:influencedBy|^dbo:influenced ?Influencer .} 

   UNION 

     {dbr:Ludwig_Wittgenstein dbo:influenced|^dbo:influencedBy ?Influenced .} 

}

#Query #DBpedia #| #^ #COUNT #UNION

Language tag
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- The current best practice for language tags is defined in RFC5646.
- [[langMATCHES]]
  - FILTER (LANG(?label) = "fr") will only return results where the language tag of ?label is @fr, while FILTER langMATCHES( LANG(?label), "fr" ) will also include those with regions such as @fr-BE.
Wikibase data model
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Wikidata label service
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- Adding "Label" to a variable will get the label of the respective item if the Wikidata Label service is called in the query. For example, for ?item, ?itemLabel will get the labels in the selected language.
- ```
SELECT ?item ?itemLabel WHERE { ?item wdt:P31 wd:Q146 . 

SERVICE wikibase:label { 
               bd:serviceParam wikibase:language “en" } 
} 
```
  #Query #Wikidata
- #+BEGIN_TIP To include a call to the Label Service in your query, just press Ctrl-Space and start typing "label" until you see the query fragment. Then change the language if needed.
  
  Check the Label service manual for other capabilities. #+END_TIP
Wikidata visualization service
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- Influence graph in the age of Enlightenment
  - pull</button> style=”width:100%;max-width:100%;height:450px” frameborder=”0”> #Wikidata #Query #FILTER #&&
- Roman diaties
  - pull</button> style=”width:100%;max-width:100%;height:450px” frameborder=”0”> #| #^ #Wikidata #Query
Properties for statements (Wikidata)
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- Item - Statement - Value - Qualifier Value
  - #Wikidata
- [[Example]]: US Presidents
  - {:height 502, :width 680}
  - With ?statement variable <iframe src="https://w.wiki/4wNL" <button class="pull-url autopull" value="https://w.wiki/4wNL"">pull style="width:100%;max-width:100%;height:450px" frameborder="0"> #Query #Wikidata #Qualifiers
  - With blank nodes <iframe src="https://w.wiki/wsi" <button class="pull-url autopull" value="https://w.wiki/wsi"">pull style="width:100%;max-width:100%;height:450px" frameborder="0"> #Query #Wikidata #Qualifiers
- See also ((61fe46bb-6fc5-4d5e-b917-d0da5b02a96a))
Providing list of input VALUES
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- ```
# Example with a block of values, where the third block in the list has no value for ?v2
VALUES (?v1 ?v2) {(:c11 :c21) (:c21 :c22) (:c21 UNDEF)}

# When value for only one variable are provided, () can be omitted 
VALUES ?v1 {:c1 :c2 :c3 :cN}
```
  #VALUES
- Get the list of notable books on linked data, semantic technologies, and semantic knowledge graphs.
  - pull</button> style=”width:100%;max-width:100%;height:450px” frameborder=”0”>
Grouping results with GROUP_CONCAT
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- ```
(GROUP_CONCAT (?V; SEPARATOR = ", ") AS ?groupV)
```
  #GROUP_CONCAT
- pull</button> style=”width:100%;max-width:100%;height:450px” frameborder=”0”> #Wikidata #Query #GROUP_CONCAT #|| #OPTIONAL
Federated queries
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Default and named graphs
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- Default graph FROM <> Used when not explicitly specified
- Named graph FROM NAMED <> Can be directly specified or through a variable
- Available named graphs at an endpoint
  - ```
  SELECT DISTINCT ?g 
   WHERE { 
      GRAPH ?g {?s ?p ?o .} 
   } 
```
  #Query #GRAPH
Other query forms
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- ASK
  - If there is at least one result
    - ASK WHERE {...}
- DESCRIBE
  - Describes a particular resource
  - All directly linked nodes
  - Not strictly specified
- [[CONSTRUCT]]
  - Create new graph from a template
  - Use SPARQL as template to
    - Copy
    - Create
    - Convert
      - From RDF to RDF
        
        Applying different ontologies
        
        Generating URIs
        
        From non-RDF to RDF (see ((654767de-a5ef-494d-8abe-66216362dd61)))
  - Result
    - Triples (virtual graph)
  - [[Example]]
    - SKOS from SKOS-XL
      - CONSTRUCT { ?concept skos:prefLabel ?prefLabel_ES .} WHERE { ?concept skosxl:prefLabel ?prefLabel . ?prefLabel skosxl:literalForm ?prefLabel_ES . FILTER (LANG(?prefLabel_ES) = "es") }
        #Query #CONSTRUCT #FILTER #LANG

SPARQL Interactions

Two triple patterns, same subject

Making another step in the graph

Three patterns and two filters

Counting and Binding

Functions on dates and times

Filtering resources with the same namespace

Negation

Optional results

Combining results

Search for string patterns

Assembling strings

Property paths

Language tag

Wikibase data model

Wikidata label service

Wikidata visualization service

Properties for statements (Wikidata)

[[Example]]: US Presidents

Providing list of input VALUES

Grouping results with GROUP_CONCAT

Federated queries

Default and named graphs

Other query forms