Nested Queries in SPARQL

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August Phillips
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2 Motivation for nested queries Query nesting enables: composition / reuse of queries rewriting / distributed execution optimization 1 / 21

3 Motivation for nested queries Query nesting enables: composition / reuse of queries rewriting / distributed execution optimization Approaches for nesting SQL: allows nesting in FROM and WHERE clauses XQuery: (arbitrary) nesting of expressions 1 / 21

4 Motivation for nested queries Query nesting enables: composition / reuse of queries rewriting / distributed execution optimization Approaches for nesting SQL: allows nesting in FROM and WHERE clauses XQuery: (arbitrary) nesting of expressions 1 / 21

5 Datasets foaf: < xmlns.com/foaf/0.1/ >. < nunolopes.org/foaf.rdf#me> a foaf:person; foaf:name "Nuno Lopes"; foaf:mbox <mailto:nuno. lopes@deri.org >; foaf:nick "nl"," nunolopes"," nlopes"; foaf:age 30; foaf:knows < < a foaf:person; foaf:name "Axel Polleres"; foaf:nick "droxel","xel","xl"; foaf:mbox <mailto:axel. polleres@deri.org >; foaf: givenname "Axel"; foaf: familyname "Polleres". 2 / 21

6 Datasets bibtex: < zeitkunst.org/bibtex /0.1/ bibtex.owl#>. < example.org/bibtex#xsparql > a bibtex:article ; bibtex: hasjournal "DERI Journal" ; bibtex:hastitle "XSPARQL" ; bibtex: hasauthor < nunolopes.org/foaf.rdf#me> ; bibtex: hasauthor < www. polleres.net/foaf.rdf#me>. 2 / 21

7 SPARQL in a nutshell 3 / 21

8 Query example Names of people age or names having (or not) an SELECT DISTINCT?Name FROM <foaf.ttl > WHERE { { {?X foaf:name?name.?x foaf:age?age FILTER (? Age >= 18 &&?Age <= 30) UNION { {?X foaf:name?name OPTIONAL {?X foaf:mbox? 4 / 21

9 Query example Names of people age or names having (or not) an SELECT DISTINCT?Name FROM <foaf.ttl > WHERE { { {?X foaf:name?name.?x foaf:age?age FILTER (? Age >= 18 &&?Age <= 30) UNION { {?X foaf:name?name OPTIONAL {?X foaf:mbox? 4 / 21

10 Query example Names of people age or names having (or not) an SELECT DISTINCT?Name FROM <foaf.ttl > WHERE { { {?X foaf:name?name.?x foaf:age?age FILTER (? Age >= 18 &&?Age <= 30) UNION { {?X foaf:name?name OPTIONAL {?X foaf:mbox? 4 / 21

11 Query example Names of people age or names having (or not) an SELECT DISTINCT?Name FROM <foaf.ttl > WHERE { { {?X foaf:name?name.?x foaf:age?age FILTER (? Age >= 18 &&?Age <= 30) UNION { {?X foaf:name?name OPTIONAL {?X foaf:mbox? 4 / 21

12 Query example Names of people age or names having (or not) an SELECT DISTINCT?Name FROM <foaf.ttl > WHERE { { {?X foaf:name?name.?x foaf:age?age FILTER (? Age >= 18 &&?Age <= 30) UNION { {?X foaf:name?name OPTIONAL {?X foaf:mbox? 4 / 21

13 Preliminaries: compatible substitutions {?X foaf:name?name.?x foaf:age?age 5 / 21

14 Preliminaries: compatible substitutions {?X foaf:name?name.?x foaf:age?age X < < Name Nuno Lopes Axel Polleres 5 / 21

15 Preliminaries: compatible substitutions {?X foaf:name?name.?x foaf:age?age X < < Name Nuno Lopes Axel Polleres X Age < / 21

16 Preliminaries: compatible substitutions {?X foaf:name?name.?x foaf:age?age X Name < Nuno Lopes < Axel Polleres X Age < / 21

17 Preliminaries: compatible substitutions {?X foaf:name?name.?x foaf:age?age X < < Name Nuno Lopes Axel Polleres X Age < 30 = X Name Age < Nuno Lopes 30 5 / 21

18 SPARQL 1.1 features Noteworthy new features in SPARQL 1.1 Aggregates Subqueries Federation Extensions Negation Expressions in the SELECT clause Property Paths Assignment 6 / 21

19 SPARQL 1.1 features Noteworthy new features in SPARQL 1.1 Aggregates Subqueries Federation Extensions Negation Expressions in the SELECT clause Property Paths Assignment 6 / 21

20 SPARQL 1.1 features Noteworthy new features in SPARQL 1.1 Aggregates Subqueries Federation Extensions Negation Expressions in the SELECT clause Property Paths Assignment 6 / 21

21 SPARQL 1.1: Nested Queries PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?y?minNick WHERE { < nunolopes.org/foaf.rdf#me> foaf:knows?y. { SELECT?y (MIN(? nick) AS?minNick) WHERE {?y foaf:nick?nick. GROUP BY?y 7 / 21

22 SPARQL 1.1: Nested Queries PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?y?minNick WHERE { < nunolopes.org/foaf.rdf#me> foaf:knows?y. { SELECT?y (MIN(? nick) AS?minNick) WHERE {?y foaf:nick?nick. GROUP BY?y 7 / 21

23 SPARQL 1.1: Nested Queries PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?y?minNick WHERE { < nunolopes.org/foaf.rdf#me> foaf:knows?y. { SELECT?y (MIN(? nick) AS?minNick) WHERE {?y foaf:nick?nick. GROUP BY?y y <nunolopes.org/foaf.rdf#me> <polleres.net/foaf.rdf#me> minnick nl droxel 7 / 21

24 SPARQL 1.1: Nested Queries PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?y?minNick WHERE { < nunolopes.org/foaf.rdf#me> foaf:knows?y. { SELECT?y (MIN(? nick) AS?minNick) WHERE {?y foaf:nick?nick. GROUP BY?y y <nunolopes.org/foaf.rdf#me> <polleres.net/foaf.rdf#me> minnick nl droxel 7 / 21

25 SPARQL 1.1: Nested Queries PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?y?minNick WHERE { < nunolopes.org/foaf.rdf#me> foaf:knows?y. { SELECT?y (MIN(? nick) AS?minNick) WHERE {?y foaf:nick?nick. GROUP BY?y y <nunolopes.org/foaf.rdf#me> <polleres.net/foaf.rdf#me> minnick nl droxel y <polleres.net/foaf.rdf#me> 7 / 21

26 SPARQL 1.1: Nested Queries PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?y?minNick WHERE { < nunolopes.org/foaf.rdf#me> foaf:knows?y. { SELECT?y (MIN(? nick) AS?minNick) WHERE {?y foaf:nick?nick. GROUP BY?y y <nunolopes.org/foaf.rdf#me> <polleres.net/foaf.rdf#me> minnick nl droxel y <polleres.net/foaf.rdf#me> y <polleres.net/foaf.rdf#me> minnick droxel 7 / 21

27 SPARQL 1.1: Nested Queries PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?y?minNick WHERE { < nunolopes.org/foaf.rdf#me> foaf:knows?y. { SELECT?y (MIN(? nick) AS?minNick) WHERE {?y foaf:nick?nick. GROUP BY?y FROM and FROM NAMED are not allowed in subqueries! 7 / 21

28 SPARQL 1.1: Federation extensions PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?name?bDay WHERE { SERVICE < example.org/foaf > {?uri foaf:name?name. SERVICE < example.org/birthdays > {?uri foaf:birthday?bday. 8 / 21

29 SPARQL 1.1: Federation extensions PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?name?bDay WHERE { SERVICE < example.org/foaf > {?uri foaf:name?name. SERVICE < example.org/birthdays > {?uri foaf:birthday?bday. 8 / 21

30 SPARQL 1.1: Federation extensions PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?name?bDay WHERE { SERVICE < example.org/foaf > {?uri foaf:name?name. SERVICE < example.org/birthdays > {?uri foaf:birthday?bday. Execution method is undefined 8 / 21

31 SPARQL 1.1: Bindings SELECT?name?bDay WHERE { SERVICE < example.org/foaf > {?uri foaf:name?name. SERVICE < example.org/birthdays > {?uri foaf:birthday?bday. BINDINGS?uri { (< nunolopes.org/foaf.rdf#me >) (< >) 9 / 21

32 SPARQL 1.1: Bindings SELECT?name?bDay WHERE { SERVICE < example.org/foaf > {?uri foaf:name?name. SERVICE < example.org/birthdays > {?uri foaf:birthday?bday. BINDINGS?uri { (< nunolopes.org/foaf.rdf#me >) (< >) allows to specify filters for a query without changing the graph pattern (good for reuse of queries) does not allow to specify values that are taken from another SPARQL query 9 / 21

33 SPARQL 1.1: Negation Negation PREFIX rdf: < - rdf -syntax -ns#> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?nick WHERE {?person foaf:nick?nick. FILTER NOT EXISTS {?uri foaf:nick "nl" 10 / 21

34 SPARQL 1.1: Negation Negation PREFIX rdf: < - rdf -syntax -ns#> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?nick WHERE {?person foaf:nick?nick. FILTER NOT EXISTS {?uri foaf:nick "nl" unbound filters remove all solutions! 10 / 21

35 SPARQL 1.1: Negation Negation PREFIX rdf: < - rdf -syntax -ns#> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?nick WHERE {?person foaf:nick?nick. FILTER NOT EXISTS {?uri foaf:nick "nl" EXISTS filter also available 10 / 21

36 SPARQL 1.1: Negation Negation PREFIX rdf: < - rdf -syntax -ns#> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?nick WHERE {?person foaf:nick?nick. FILTER NOT EXISTS {?uri foaf:nick "nl" Removing solutions PREFIX : < example/> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT DISTINCT?name WHERE {?person foaf:name?name. MINUS {?person foaf: givenname "Axel". 10 / 21

37 SPARQL 1.1: Negation Negation PREFIX rdf: < - rdf -syntax -ns#> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?nick WHERE {?person foaf:nick?nick. FILTER NOT EXISTS {?uri foaf:nick "nl" Removing solutions PREFIX : < example/> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT DISTINCT?name WHERE {?person foaf:name?name. MINUS {?person foaf: givenname "Axel". Removes compatible solutions: requires shared variables! 10 / 21

38 SPARQL 1.1: Expressions in SELECT Creating new values PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?person (CONCAT(?given, " ",?family) AS?fullName) FROM <foaf.ttl > WHERE {?person foaf: givenname?given; foaf: familyname?family 11 / 21

39 Nested Queries in SPARQL: Extensions Types of nesting SPARQL From : Subqueries in dataset clauses SPARQL SubS : Subqueries as graph patterns. SPARQL Filter : Subqueries in filter constraints. 12 / 21

40 SPARQL from Query in the FROM clause SELECT?M1?M2 FROM <foaf.ttl > FROM ( CONSTRUCT {?A1 co-author?a2 FROM <bib.ttl > WHERE {?Pub author?a1.?pub author?a2. FILTER (!(?A1 =?A2)) ) WHERE {?P1 co-author?p2.?p1 mail?m1.?p2 mail?m2 13 / 21

41 SPARQL from Query in the FROM clause SELECT?M1?M2 FROM <foaf.ttl > FROM ( CONSTRUCT {?A1 co-author?a2 FROM <bib.ttl > WHERE {?Pub author?a1.?pub author?a2. FILTER (!(?A1 =?A2)) ) WHERE {?P1 co-author?p2.?p1 mail?m1.?p2 mail?m2 Natural extension: CONSTRUCT returns an RDF graph Side effect: adds construction of values 13 / 21

42 SPARQL SubS Nested query in the graph pattern SELECT?Mail FROM <foaf.ttl > WHERE { {?X mail?mail. {( SELECT DISTINCT?X FROM <bib.ttl > WHERE {?Pub author?x) 14 / 21

43 SPARQL SubS Nested query in the graph pattern SELECT?Mail FROM <foaf.ttl > WHERE { {?X mail?mail. {( SELECT DISTINCT?X FROM <bib.ttl > WHERE {?Pub author?x) projection of variables in graph patterns datasets in nested queries 14 / 21

44 SPARQL filter Nested queries in FILTER expressions SELECT?Name FROM <bib.ttl > WHERE {?Aut name?name.?pub author?aut.?pub conf?conf FILTER (? Conf IN ( SELECT?ConfX FROM <bib.ttl > WHERE {?ConfX series "ISWC" )) 15 / 21

45 SPARQL filter Nested queries in FILTER expressions SELECT?Name FROM <bib.ttl > WHERE {?Aut name?name.?pub author?aut.?pub conf?conf FILTER (? Conf IN ( SELECT?ConfX FROM <bib.ttl > WHERE {?ConfX series "ISWC" )) Duplicate elimination (without DISTINCT) Similar to subqueries in SQL: introduces IN, SOME, ALL and EXITS operators 15 / 21

46 Shameless self-promotion: Nesting in XSPARQL XSPARQL follows a different semantics for nesting Based on XQuery nesting Variables are correlated Top-down evaluation 16 / 21

47 XSPARQL Nested Queries: XSPARQL From Nesting in FROM clauses prefix : < zeitkunst.org/bibtex /0.1/ bibtex.owl#> prefix foaf: < xmlns.com/foaf/0.1/ > let $ds := construct { $A1 :co-author $A2 from <bib.ttl > where { $Pub : hasauthor $A1. $Pub : hasauthor $A2. filter (!($A1 = $A2)) for $M1 $M2 from <foaf.ttl > from $ds where { $P1 :co-author $P2. $P1 foaf:mbox $M1. $P2 foaf:mbox $M2 return ($M1, $M2) 17 / 21

48 XSPARQL Nested Queries: XSPARQL From Nesting in FROM clauses prefix : < zeitkunst.org/bibtex /0.1/ bibtex.owl#> prefix foaf: < xmlns.com/foaf/0.1/ > let $ds := construct { $A1 :co-author $A2 from <bib.ttl > where { $Pub : hasauthor $A1. $Pub : hasauthor $A2. filter (!($A1 = $A2)) for $M1 $M2 from <foaf.ttl > from $ds where { $P1 :co-author $P2. $P1 foaf:mbox $M1. $P2 foaf:mbox $M2 return ($M1, $M2) 17 / 21

49 XSPARQL Nested Queries: XSPARQL SubS Nesting in WHERE clauses for distinct $X from <bib.ttl > where { $Pub author $X return for $Mail from <foaf.ttl > where { $X mail $Mail. return $Mail 18 / 21

50 XSPARQL: endpoint/service queries SPARQL 1.1 SERVICE PREFIX dbpedia2: < dbpedia.org/property/> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?N?MyB FROM < polleres.net/foaf.rdf > WHERE { [ foaf:birthday?myb ]. SERVICE < dbpedia.org/sparql > { SELECT?N WHERE { [ dbpedia2:born?b; foaf:name?n ]. FILTER ( Regex(Str(?B),str(? MyB)) ) 19 / 21

51 XSPARQL: endpoint/service queries SPARQL 1.1 SERVICE PREFIX dbpedia2: < dbpedia.org/property/> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?N?MyB FROM < polleres.net/foaf.rdf > WHERE { [ foaf:birthday?myb ]. SERVICE < dbpedia.org/sparql > { SELECT?N WHERE { [ dbpedia2:born?b; foaf:name?n ]. FILTER ( Regex(Str(?B),str(? MyB)) ) 19 / 21

52 XSPARQL: endpoint/service queries SPARQL 1.1 SERVICE PREFIX dbpedia2: < dbpedia.org/property/> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?N?MyB FROM < polleres.net/foaf.rdf > WHERE { [ foaf:birthday?myb ]. SERVICE < dbpedia.org/sparql > { SELECT?N WHERE { [ dbpedia2:born?b; foaf:name?n ]. FILTER ( Regex(Str(?B),str(? MyB)) ) 19 / 21

53 XSPARQL: endpoint/service queries SPARQL 1.1 SERVICE PREFIX dbpedia2: < dbpedia.org/property/> PREFIX foaf: < xmlns.com/foaf/0.1/ > SELECT?N?MyB FROM < polleres.net/foaf.rdf > WHERE { [ foaf:birthday?myb ]. SERVICE < dbpedia.org/sparql > { SELECT?N WHERE { [ dbpedia2:born?b; foaf:name?n ]. FILTER ( Regex(Str(?B),str(? MyB)) ) Result limits from SPARQL endpoints prevent this query from working! 19 / 21

54 XSPARQL: endpoint/service queries XSPARQL endpoint prefix dbprop: < dbpedia.org/ property/> prefix foaf: < xmlns.com/foaf/0.1/ > prefix : < xsparql.deri.org/bday#> let $MyB := for * from < polleres.net/foaf.rdf > where { [ foaf:birthday $B ]. return $B for * from < dbpedia.org/> endpoint < dbpedia.org/sparql > where { [ dbprop:born $B; foaf:name $N ]. filter ( regex(str($b),str($myb)) ) construct { :axel : samebirthdayas $N 20 / 21

55 XSPARQL: endpoint/service queries XSPARQL endpoint prefix dbprop: < dbpedia.org/ property/> prefix foaf: < xmlns.com/foaf/0.1/ > prefix : < xsparql.deri.org/bday#> let $MyB := for * from < polleres.net/foaf.rdf > where { [ foaf:birthday $B ]. return $B for * from < dbpedia.org/> endpoint < dbpedia.org/sparql > where { [ dbprop:born $B; foaf:name $N ]. filter ( regex(str($b),str($myb)) ) construct { :axel : samebirthdayas $N 20 / 21

56 Conclusions Query nesting is a much needed feature SPARQL 1.1 s nesting is still quite limited (e.g. no injection of values) Other approches for nesting can be considered SPARQL Filter is doable in XSPARQL but ugly! Possible (syntactic) extensions of nesting for XSPARQL 21 / 21

SPARQL. Fausto Giunchiglia and Mattia Fumagallli. University of Trento

SPARQL. Fausto Giunchiglia and Mattia Fumagallli. University of Trento SPARQL Fausto Giunchiglia and Mattia Fumagallli University of Trento Roadmap Introduction Basic query forms SELECT CONSTRUCT ASK DESCRIBE Other clauses and modifiers SPARQL Federated Query Exercises 2