querying linked data

Querying Linked Data

Presented by:Barry Norton

2

Motivation: Music!

Visualization Module

Metadata

Streaming providers

Physical Wrapper

Downloads

Dat

a ac

quis

ition

D2R Transf.LD Wrapper

Musical Content

Appl

icati

on

Analysis & Mining Module

LD D

atas

etAc

cess

LD Wrapper

RDF/ XML

Integrated Dataset

Interlinking CleansingVocabulary Mapping

SPARQL Endpoint

Publishing

RDFa

Other content

EUCLID - Querying Linked Data 3

Agenda

1. Introduction to SPARQL

2. Querying Linked Data with SPARQL

3. SPARQL Algebra

4. Updating Linked Data with SPARQL 1.1

5. SPARQL Protocol

6. Reasoning over Linked Data

4

INTRODUCTION TO SPARQL

EUCLID - Querying Linked Data

5

SPARQL


Semantic Web StackBerners-Lee (2006)

* Protocol and RDF Query Language

Declarative query language

6

SPARQL


• SPARQL Query– Declarative query language for RDF data– http://www.w3.org/TR/rdf-sparql-query/

• SPARQL Algebra– Standard for communication between SPARQL services and clients– http://www.w3.org/2001/sw/DataAccess/rq23/rq24-algebra.html

• SPARQL Update– Declarative manipulation language for RDF data– http://www.w3.org/TR/sparql11-update/

• SPARQL Protocol– Standard for communication between SPARQL services and clients– http://www.w3.org/TR/sparql11-protocol/

7

SPARQL Query 1.1


• SPARQL 1.0 only allows accessing the data (query)

• SPARQL 1.1 introduces:

Query extensions

Updates

• Data management: Insert, Delete, Delete/Insert

• Graph management: Create, Load, Clear, Drop, Copy, Move, Add

• Aggregates, Subqueries, Negation, Expressions in the SELECT clause, Property paths, assignment, short form for CONSTRUCT, expanded set of functions and operators

Federation extension • Service, values, service variables (informative) CH 5

8

SPARQL Basics


• RDF triple: Basic building block, of the form subject, predicate, object. Example:

• RDF triple pattern: Contains one or more variables. Examples:

• RDF quad pattern: Contains graph name: URI or variable. Examples:

dbpedia:The_Beatles foaf:name "The Beatles" .

dbpedia:The_Beatles foaf:made ?album.

?album mo:track ?track .

?album ?p ?o .

GRAPH <:g> {:s :p :o .}GRAPH ?g {dbpedia:The_Beatles foaf:name ?o.}

9

SPARQL Basics


• RDF graph: Set of RDF assertions, manipulated as a labeled directed graph.

• RDF data set: set of RDF triples. It is comprised of:• One default graph• Zero or more named graphs

• SPARQL protocol client: HTTP client that sends requests for SPARQL Protocol operations (queries or updates)

• SPARQL protocol service: HTTP server that services requests for SPARQL Protocol operations

• SPARQL endpoint: The URI at which a SPARQL Protocol service listens for requests from SPARQL clients

10

QUERYING LINKED DATA WITH SPARQL


11

SPARQL Query


Main idea: Pattern matching• Queries describe sub-graphs of the queried graph• Graph patterns are RDF graphs specified in Turtle

syntax, which contain variables (prefixed by either “?” or “$”)

• Sub-graphs that match the graph patterns yield a result

?albumdbpedia: The_Beatles

foaf:made

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SPARQL Query


?albumdbpedia: The_Beatles

foaf:made

dbpedia: The_Beatlesfoaf:made

<http://musicbrainz.org

/record/...>


/record/...>

foaf:madeData:

Graph pattern: Results:

"Help!" "Let It Be"

dc:title dc:title


/record/...>

"Abbey Road"

dc:title

foaf:made

?album

<http://musicbrainz.org...>



13

SPARQL Query


?album

dbpedia: The_Beatles

foaf:made



/record/...>


/record/...>

foaf:madeData:


"Help!" "Let It Be"

dc:title dc:title


/record/...>

"Abbey Road"

dc:title

foaf:made

?album ?title

<http://...> "Help!"

<http://...> "Abbey Road"

<http://...> "Let It Be"?title

dc:title

14

SPARQL Query


?album


foaf:made



/record/...>


/track/...>

foaf:madeData:


"Help!" "Help!"

dc:title dc:title

mo:track

a

mo:Record mo:Track

mo:Record

?album


15

SPARQL Query: Components


PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX mo: <http://purl.org/ontology/mo/>

SELECT ?albumFROM <http://musicbrainz.org/20130302>WHERE { dbpedia:The_Beatles foaf:made ?album . ?album a mo:Record ; dc:title ?title} ORDER BY ?title

Prologue:• Prefix definitions• Subtly different from Turtle syntax - the final period is not used

16



Query form:• ASK, SELECT, DESCRIBE or CONSTRUCT• SELECT retrieves variables and their bindings as a table



17



Data set specification:• This clause is optional• FROM or FROM NAMED• Indicates the sources for the data against which to find matches



18



Query pattern:• Defines patterns to match against the data• Generalises Turtle with variables and keywords – N.B. final period optional



19

Solution modifier:• Modify the result set• ORDER BY, LIMIT or OFFSET re-organise rows; • GROUP BY combines them





20

Query Forms


SPARQL supports different query forms:

• ASK tests whether or not a query pattern has a solution. Returns yes/no

• SELECT returns variables and their bindings directly

• CONSTRUCT returns a single RDF graph specified by a graph template

• DESCRIBE returns a single RDF graph containing RDF data about resource

21

Query Form: ASK


• Namespaces are added with the ‘PREFIX’ directive• Statement patterns that make up the graph are

specified between brackets (“{}”)

PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX dbpedia-ont: <http://dbpedia.org/ontology/>PREFIX mo: http://purl.org/ontology/mo/ASK WHERE { dbpedia:The_Beatles mo:member dbpedia:Paul_McCartney.}

Is Paul McCartney member of ‘The Beatles’?Query: true

Results:

Is Elvis Presley member of ‘The Beatles’?Query: false

Results: PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX dbpedia-ont: <http://dbpedia.org/ontology/>PREFIX mo: http://purl.org/ontology/mo/ASK WHERE { dbpedia:The_Beatles mo:member dbpedia:Elvis_Presley.}

22

Query Form: SELECT


• The solution modifier projection nominates which components of the matches should be returned

• “*” means all components should be returned

PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX mo: <http://purl.org/ontology/mo/>SELECT ?album_name ?track_titleWHERE { dbpedia:The_Beatles foaf:made ?album . ?album dc:title ?album_name ; mo:track ?track . ?track dc:title ?track_title .}

Query: What albums and tracks did ‘The Beatles’ make?

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Filter expressions• Different types of filters and functions may be used

Query Form: SELECT (2)


PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX mo: <http://purl.org/ontology/mo/>SELECT ?album_name ?track_title ?date ?durationWHERE { dbpedia:The_Beatles foaf:made ?album . ?album dc:title ?album_name ; mo:track ?track . ?track dc:title ?track_title ;

mo:duration ?duration; FILTER (?duration>300000 && ?duration<400000) }

Query:

Filter: Comparison and logical operatorsRetrieve the albums and tracks recorded by ‘The Beatles’, where the duration of the song is more than 300 secs. and no longer than 400 secs.

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Elimination of duplicates

PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX mo: <http://purl.org/ontology/mo/>SELECT MODIFIER ?album_nameWHERE { dbpedia:The_Beatles foaf:made ?album . ?album dc:title ?album_name .

mo:track ?track1 . mo:track ?track2 .

FILTER (?track1 != ?track2) }

Retrieve the name of the albums recorded by ‘The Beatles’ which have at least two different songs.Query:

?album

“Revolver”

“Sessions”

“Abbey Road”

?album

“Revolver”

“Revolver”

“Revolver”

“Sessions”

“Abbey Road”

“Abbey Road”

DISTINCT

Results:

REDUCEDMODIFIER= MODIFIER=

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Aggregates• Calculate aggregate values: COUNT, SUM, MIN, MAX, AVG,

GROUP_CONCAT and SAMPLE• Built around the GROUP BY operator• Prune at group level (cf. FILTER) using HAVING



PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX mo: <http://purl.org/ontology/mo/>SELECT ?album (SUM(?track_duration) AS ?album_duration)WHERE { dbpedia:The_Beatles foaf:made ?album . ?album mo:track ?track . ?track mo:duration ?track_duration .} GROUP BY ?album HAVING (SUM(?track_duration) > 3600000)

Retrieve the duration of the albums recorded by ‘The Beatles’.Query:

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Query Form: DESCRIBE


Takes the resources within the solution, and provides information about them as RDF statements. They can be identified by:• Specifying explicit IRIs

• Bindings of variables in the WHERE clause

PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX mo: <http://purl.org/ontology/mo/>DESCRIBE ?memberWHERE { dbpedia:The_Beatles mo:member ?member .}

PREFIX dbpedia: <http://dbpedia.org/resource/>DESCRIBE dbpedia:Paul_McCartney

27EUCLID - Querying Linked Data

• CONSTRUCT WHERE: In order to query for a subgraph, without change, it is no longer necessary to repeat the graph pattern in the template

PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX mo: <http://purl.org/ontology/mo/>PREFIX dc: <http://purl.org/dc/elements/1.1/>CONSTRUCT WHERE { dbpedia:The_Beatles foaf:made ?album . ?album mo:track ?track .}

Example:

Query Form: CONSTRUCT

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Query Form: CONSTRUCT (2a)




/record/...>


/record/...>

foaf:madeData:

Query: Result:

"Help!" "Let It Be"

dc:title dc:title


/record/...>

"Abbey Road"

dc:title

foaf:made

CONSTRUCT { ?album dc:creator dbpedia:The_Beatles .}WHERE { dbpedia:The_Beatles foaf:made ?album .}


<http://musicbrainz

…>

<http://musicbrainz

…><http://

musicbrainz…>

dc:creator

dc:creator

dc:creator


• Returns RDF statements created from variable bindings

• Template: graph pattern with variables from the query pattern

PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX mo: <http://purl.org/ontology/mo/>PREFIX dc: <http://purl.org/dc/elements/1.1/>CONSTRUCT { ?album dc:creator dbpedia:The_Beatles . ?track dc:creator dbpedia:The_Beatles .}WHERE { dbpedia:The_Beatles foaf:made ?album . ?album mo:track ?track .}

Create the dc:creator descriptions for albums and their tracks recorded by ‘The Beatles’.Query:

Query Form: CONSTRUCT (2b)

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Query Form: CONSTRUCT (3)


Subsets of results• It is possible to combine the query with solution modifiers

(ORDER BY, LIMIT, OFFSET)

PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX mo: <http://purl.org/ontology/mo/>PREFIX dc: <http://purl.org/dc/elements/1.1/>CONSTRUCT { ?album dc:creator dbpedia:The_Beatles . ?track dc:creator dbpedia:The_Beatles .}WHERE { dbpedia:The_Beatles foaf:made ?album . ?album mo:track ?track ; dc:date ?date .} ORDER BY DESC(?date) LIMIT 10

Create the dc:creator descriptions for the 10 most recent albums and their tracks recorded by ‘The Beatles’.Query:

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Union Graph Pattern• Allows the specification of alternatives (disjunctions)


PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: http://xmlns.com/foaf/0.1/PREFIX dc: <http://purl.org/dc/elements/1.1/>CONSTRUCT { ?album dc:creator dbpedia:The_Beatles . ?track dc:creator dbpedia:The_Beatles .}WHERE { dbpedia:The_Beatles foaf:made ?album . ?album dc:title ?album_name . {?album dbpedia-ont:recordedIn dbpedia:Abbey_Road_Studios .}

UNION {?album dbpedia-ont:recordedIn dbpedia:Trident_Studios .}}

Create the dc:creator descriptions for the albums recorded by ‘The Beatles’ in ‘Abbey Road Studios’ or ‘Trident Studios’ Query:


http://xmlns.com/foaf/0.1/

32

Filter expressions• Different types of filters and functions may be used


PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc: <http://purl.org/dc/elements/1.1/>CONSTRUCT {?album dc:creator dbpedia:The_Beatles .}WHERE { dbpedia:The_Beatles foaf:made ?album . ?album dc:title ?album_name ; FILTER (REGEX(?album_name, ".*love.*", i)) }

Query:

Filter: Regular expressions over stringsCreate the dc:creator descriptions of the albums recorded by ‘The Beatles’ whose title contains the word ‘love .


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Type of function Function Result type

Functional Forms

boundIFCOALESCENOT EXISTS, EXISTSor, andRDFTerm-equal (=), sameTermIN, NOT IN

xsd:booleanrdfTermrdfTermxsd:booleanxsd:booleanxsd:booleanboolean

Functions on RDF TermsisIRI, isBlank, isLiteral, isNumericstr, lang,datatypeIRIBNODE

xsd:booleansimple literaliriiriblank node

Functions on Numerics ABS, ROUND, CEIL, FLOORRAND

numericxsd:double

Filter expressions

EUCLID - Querying Linked DataSource:http://www.w3.org/TR/sparql11-query/#SparqlOps


34

Type of function Function Result type

Functions on Strings STRLENSUBSTR, UCASE, LCASESTRSTARTS, STRENDS, CONTAINSSTRBEFORE, STRAFTERENCODE_FOR_URICONCATlangMatchesREGEXREPLACE

xsd:integerstring literalxsd:booleanliteralsimple literalstring literalxsd:booleanxsd:booleanstring literal

Functions on Dates and Times

nowyear, month, day, hours, minutessecondstimezonetz

xsd:dateTimexsd:integerxsd:decimalxsd:dayTimeDurationsimple literal

Filter expressions


Source:http://www.w3.org/TR/sparql11-query/#SparqlOps


35

Optional Graph Pattern• OPTIONAL clause encloses the optional parts• If variables in the construct clause are not bound in the optional,

the triple patterns with these variables are not generated


PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX dbpedia-owl: <http://dbpedia.org/ontology/>CONSTRUCT { ?album dc:creator ?artist . ?picture dc:depicts ?artist . }WHERE { ?artist foaf:made ?album . OPTIONAL {?artist foaf:depiction ?picture .}}

Create the dc:creator and dc:depicts descriptions of artists.Query:


36

Optional Graph Pattern• Can test if variables are bound in filter expressions• Solutions that meet the OPTIONAL clause can be filtered out by

using the logical filter NOT (!)


PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX dbpedia-owl: <http://dbpedia.org/ontology/>CONSTRUCT { ?album dc:creator ?artist . }WHERE { ?artist foaf:made ?album . OPTIONAL {?artist dbpedia-owl:deathPlace ?place_of_death .} FILTER (!BOUND(?place_of_death))}

Create the dc:creator descriptions of those artists who are not dead.

Query:


NOT EXISTS {?artist dbpedia-owl:deathPlace ?place_of_death .}

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Assigning Variables • The value of an expression can be added to a solution mapping by

binding a new variable (which can be further used and returned)• The BIND form allows to assign a value to a variable from a BGP


PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX mo: <http://purl.org/ontology/mo/>PREFIX dbpedia-ont: <http://dbpedia.org/ontology/>CONSTRUCT { ?track dbpedia-ont:runtime ?secs .} WHERE { dbpedia:The_Beatles foaf:made ?album . ?album mo:track ?track . ?track mo:duration ?duration . BIND((?duration/1000) AS ?secs) .}

Calculate the duration of the tracks from ms to s, and store the value using the dbpedia-ont:runtime property .

Query:


38

Sub-queries and Aggregate Values• To combine the CONSTRUCT query form with aggregate values, a

sub-query should be created inside the WHERE clause


PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX mo: <http://purl.org/ontology/mo/>CONSTRUCT {?album music-ont:duration ?album_duration .}WHERE { SELECT ?album (SUM(?track_duration) AS ?album_duration) { dbpedia:The_Beatles foaf:made ?album . ?album mo:track ?track . ?track mo:duration ?track_duration . } GROUP BY ?album HAVING (SUM(?track_duration) > 3600000)}

Materialize the duration of the albums recorded by ‘The Beatles’.Query:


39

UPDATING LINKED DATA WITH SPARQL 1.1


40

Data Management


SPARQL 1.1 provides data update operations:

• INSERT data: adds some triples, given inline in the request, into a graph

• DELETE data: removes some triples, given inline in the request, if the respective graphs contains those

• DELETE/INSERT data: uses in parallel INSERT and DELETE

CH 1

CH 1

41

Data Management (2)


INSERT data

PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>

INSERT DATA { GRAPH { <http://musicbrainz.org/20130302> <http://musicbrainz.org/artist/b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d> foaf:made <http://musicbrainz.org/release/3a685770-7326-34fc-9f18-e5f5626f3dc5> ,

< http://musicbrainz.org/release/cb6f8798-d51e-4fa5-a4d1-2c0602bfe1b6 > .

<http://musicbrainz.org/release/3a685770-7326-34fc-9f18-e5f5626f3dc5> dc:title "Please Please Me".

< http://musicbrainz.org/release/cb6f8798-d51e-4fa5-a4d1-2c0602bfe1b6 >

dc:title "Something New". } }

Insert the following albums recorded by The Beatles into the graphhttp://musicbrainz.org/20130209-004702

CH 1

42

Data Management (3)


DELETE data Delete all the information about the album Casualities of The Beatles.

PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>

DELETE { ?album ?predicate ?object . }WHERE {<http://musicbrainz.org/artist/b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d> foaf:made ?album .?album dc:title "Casualities". ?album ?predicate ?object .}

CH 1

43

Data Management (4)


DELETE/INSERT data

PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX db-ont: <http://dbpedia.org/ontology/>PREFIX foaf: <http://xmlns.com/foaf/0.1/>

DELETE { dbpedia:The_Beatles db-ont:currentMember ?x . }INSERT { GRAPH <http://musicbrainz.org/20130209-004702> { dbpedia:The_Beatles db-ont:formerBandMember ?x .} }WHERE { dbpedia:The_Beatles db-ont:currentMember ?x . ?x foaf:name "Peter Best" .}

Delete the status of ‘Peter Best’ as current member of´The Beatles´, and insert his status as former member of the band.

44

Graph Management


SPARQL 1.1 provides graph update operations:

• CREATE: creates an empty graph in the Graph Store

• LOAD: reads the content of a document into a graph in the Graph Store

• CLEAR: removes all triples in one or more graphs

• DROP: removes the graph from the Graph Store

• Other operations: COPY, MOVE, ADD

45

Graph Management (2)


CREATE• Creates a new named graph• Can be used with the DEFAULT and ALL keywords

LOAD• An RDF graph can be loaded from a URL

• LOAD can be used with the SILENT keyword

CREATE GRAPH <http://musicbrainz.org/20130302>

LOAD <http://xmlns.com/foaf/spec/20100809.rdf>

LOAD <http://xmlns.com/foaf/spec/20100809.rdf> INTO <http://xmlns.com/foaf/0.1/>

Named graph

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CLEAR• Removes all triples in the graph (it is emptied but not deleted!) • The graph(s) can be specified with the following keywords:

DEFAULT, NAMED, ALL, GRAPH • Can be used with the SILENT keyword

DROP• The given graph is removed from the Graph Store, including its

content• Can be used with the DEFAULT and ALL keywords

CLEAR GRAPH <http://musicbrainz.org/20130302>

DROP GRAPH <http://musicbrainz.org/20130302>

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SPARQL 1.1 provides other graph management operations:

• COPY … TO …

• MOVE … TO …

• ADD … TO …

COPY GRAPH <http://musicbrainz.org/20130302>TO GRAPH <http://musicbrainz.org/20130303>

MOVE GRAPH <http://musicbrainz.org/temp>TO GRAPH <http://musicbrainz.org/20130303>

ADD GRAPH <http://musicbrainz.org/20130302>TO GRAPH <http://musicbrainz.org/20130303>

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SPARQL PROTOCOL FOR RDF


49

SPARQL 1.1. Protocol


• Consists of two operations: query and update

• An operation defines:• The HTTP method (GET or POST)• The HTTP query string parameters• The message content included in the HTTP request body• The message content included in the HTTP response body

SPARQL Client SPARQL EndpointRequest

alt [no errors]

[else]

Success Response

Failure Response


• Sends a SPARQL query to a service and receives the results of the query

• The response is:

• May be invoked using HTTP GET or HTTP POST. The method POST with URL encoding is mostly used when the query string is too long

Query Operation

XML, JSON, CSV/TSV from a SELECT query

RDF/XML, Turtle from a CONSTRUCT query


Example:

PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX dbpedia-ont: <http://dbpedia.org/ontology/>SELECT ?album WHERE { ?album dbpedia-ont:artist dbpedia:The_Beatles .} LIMIT 3

SPARQL Query:

Query Operation (2)

HTTP GET request:

Try this query! (Click on the hurl icon)

http://www.hurl.it/hurls/901bced6d77240a9dc4c9a11f293e885a639b5e9/b764454c05f3eb3a02f0873ff0403f357e94c743

52

Update Operation


• Sends a SPARQL update request to a service

• Should be invoked using the HTTP PATCH/POST method

• The response consists of a HTTP response status code, which indicates success or failure of the operation

53

REASONING OVER LINKED DATA


54

Reasoning forLinked Data Integration


• Example: Integration of the MusicBrainz data set and the DBpedia data set

IntegrationData set Data set

55



mo:b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d foaf:name The Beatles; mo:member mo:ba550d0e-adac-4864-b88b-407cab5e76af; mo:member mo:4d5447d7-c61c-4120-ba1b-d7f471d385b9; mo:member mo:42a8f507-8412-4611-854f-926571049fa0; mo:member mo:300c4c73-33ac-4255-9d57-4e32627f5e13.

dbpedia:The_Beatles dbpedia-ont:origin dbpedia:Liverpool; dbpedia-ont:genre dbpedia:Rock_music; foaf:depiction .

IntegrationData set Data set

same

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mo:b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d foaf:name The Beatles; mo:member mo:ba550d0e-adac-4864-b88b-407cab5e76af; mo:member mo:4d5447d7-c61c-4120-ba1b-d7f471d385b9; mo:member mo:42a8f507-8412-4611-854f-926571049fa0; mo:member mo:300c4c73-33ac-4255-9d57-4e32627f5e13.

dbpedia:The_Beatles dbpedia-ont:origin dbpedia:Liverpool; dbpedia-ont:genre dbpedia:Rock_music; foaf:depiction .

same

SELECT ?m ?g WHERE { dbpedia:The_Beatles dbpedia-ont:genre ?g; mo:member ?m.}

Query: ?m ?g

mo:ba550d0e-adac-4864-b88b-407cab5e76af

dbpedia:Rock_music

mo:4d5447d7-c61c-4120-ba1b-d7f471d385b9

dbpedia:Rock_music

mo42a8f507-8412-4611-854f-926571049fa0;

dbpedia:Rock_music

mo300c4c73-33ac-4255-9d57-4e32627f5e13

dbpedia:Rock_music

Result set:

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SPARQL 1.1:Entailment Regimes


• SPARQL 1.0 was defined only for simple entailment (pattern matching )

• SPARQL 1.1 is extended with entailment regimes other than simple entailment:– RDF entailment– RDFS entailment– D-Entailment– OWL RL entailment– OWL Full entailment– OWL 2 DL, EL, and QL entailment– RIF entailmentSource: http://www.w3.org/TR/rdf-mt/#RDFSRules

58

RDFS


Resource Description Framework Schema


Taxonomies and inferences

59

RDFS Entailment Regimes


• Contains 13 entailment rules denominated rdfsi for inference over RDFS definitions*:– rdfs:Literal (rdfs1, rdfs13)

– rdfs:domain (rdfs2), rdfs:range (rdfs3)

– rdfs:Resource (rdfs4a, rdfs4, rdfs8)

– rdfs:subPropertyOf (rdfs5, rdfs6, rdfs7, rdfs12)

– rdfs:Class (rdfs8, rdfs10)

– rdfs:subClassOf (rdfs9, rdfs10, rdfs11)

– rdfs:ContainerMembershipProperty (rdfs12)

– rdfs:Datatype (rdfs13)* Source: http://www.w3.org/TR/rdf-mt/#RDFSRules

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rdfs2 – rdfs:domain



dbpedia: Paul_McCartney

SELECT ?x WHERE { ?x a mo:MusicGroup.}

mo:member rdfs:domain mo:MusicGroup .

?x ?x

dbpedia:The_Beatles …

mo:member

Schema: Query:

Result set: Result set with inference:

dbpedia: John_Lennon

dbpedia: George_Harrison

dbpedia: Ringo_Starr

mo:member mo:member

mo:member

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rdfs3 – rdfs:range




SELECT ?x WHERE { ?x a foaf:Agent.}

mo:member rdfs:range foaf:Agent .

?x ?x

dbpedia:Paul_McCartney

dbpedia:John_Lennon

dbpedia:Ringo_Starr

dbpedia:George_Harrison …

dbpedia-ont:bandMember

Schema: Query:








62

rdfs7 – rdfs:subPropertyOf


dbpedia: Yesterday


SELECT ?x WHERE { dbpedia:Yesterday mo:performer ?x.}

mo:singer rdfs:subPropertyOf mo:performer .

?x

dbpedia:John_Lennon

dbpedia:Ringo_Starr

dbpedia:George_Harrison

?x

dbpedia:John_Lennon

dbpedia:Ringo_Starr



mo:singer

Schema: Query:





mo:performer mo:performermo:performer

mo:performer

63

rdfs9 – rdfs:subClassOf



SELECT ?x WHERE { ?x a mo:MusicArtist.}

mo:MusicGroup rdfs:subClassOf mo:MusicArtist .

?x ?x

dbpedia:The_Beatles …

Schema: Query:


mo: MusicArtist

rdf:type

mo: MusicGroup

rdf:type

64

Inference from Schema


• Knowledge encoded in the schema leads to infer new facts

• This is also captured in the set of axiomatic triples, which provide basic meaning for all the vocabulary terms

mo:MusicGroup rdfs:subClassOf mo:MusicArtist .

mo:MusicGroup a rdfs:Class .mo:MusicArtist a rdfs:Class .

Schema:

Inferred

facts:

rdfs:subClassOf rdfs:domain rdfs:Class .

rdfs:subClassOf rdfs:range rdfs:Class .

65

RDFS: Lack of Consistency Check


• It is possible to infer facts that seem incorrect facts, but RDFS cannot prevent this:

Schema: mo:member rdfs:domain mo:MusicGroup ;

rdfs:range foaf:Agent .

Existing :PaulMcCartney a :SoloMusicArtist ; facts: :member :TheBeatles .

Inferred :PaulMcCartney a :MusicGroup . facts:

No contradiction!:The mis-modeling is not diagnosed

rdfs2

66

• We might wish further inferences, but these are beyond the entailment rules implemented by RDFS

RDFS: Inference Limitations


foaf:knows rdfs:domain foaf:Person ; rdfs:range foaf:Person .

foaf:made rdfs:domain foaf:Agent . :PaulMcCartney foaf:made :Yesterday ; foaf:knows :RingoStarr .

:PaulMcCartney a foaf:Agent ; a foaf:Person .:RingoStarr a foaf:Person .

Schema:

Existing fact:

Inferred

facts:

:Yesterday dc:creator :PaulMcCartney.:RingoStarr foaf:knows :PaulMcCartney . These inferences require OWL!

NOT inferre

d:

Cannot model with RDFS that ‘x knows y’ implies ‘y knows x’

Cannot model with RDFS that if ‘x makes y’ implies that ‘the creator of y is x’

67

OWL


Web Ontology Language


Ontologies and inferences

68

Introduction to OWL


• Provides more ontological constructs and avoids some of the potential confusion in RDFS

• OWL 2 is divided into sub-languages denominated profiles:– OWL 2 EL: Limited to basic classification,

but with polynomial-time reasoning

– OWL 2 QL: Designed to be translatable to relational database querying

– OWL 2 RL: Designed to be efficiently implementable in rule-based systems

• Most triple stores concentrate on the use of RDFS with a subset of OWL features, called OWL-Horst or RDFS++

More restrictive than OWL DL

69

OWL Properties


OWL distinguishes between two types of properties:• OWL ObjectProperties: resources as values• OWL DatatypeProperties: literals as values

:plays rdf:type owl:ObjectProperty;rdfs:domain :Musician;

rdfs:range :Instrument .

:hasMembers rdf:type owl:DatatypeProperty; rdfs:domain :MusicGroup

rdfs:range xsd:int .

70

Property Axioms


• Property axioms include those from RDF Schema• OWL allows for property equivalence. Example:EquivalentObjectProperties(dbpedia-ont:bandMember mo:member)

dbpedia-ont:bandMember owl:equivalentProperty mo:member.

≡



mo:member




mo:member

mo:member

mo:member

SELECT ?x {dbpedia:The_Beatles dbpedia-ont:bandMember ?x.}

Query:

?xResult set:

?x


dbpedia:John_Lennon

dbpedia:Ringo_Starr


Result set with inference:

71

Property Axioms


• Property axioms include those from RDF Schema• OWL allows for property equivalence. Example:EquivalentObjectProperties(dbpedia-ont:bandMember mo:member)

dbpedia-ont:bandMember owl:equivalentProperty mo:member.

• OWL allows for property disjointness. Example: DisjointObjectProperty(dbpedia-ont:length mo:duration)

dbpedia-ont:length owl:propertyDisjointWith mo:duration.

• There is no standard for implementing inconsistency reports under SPARQL

≡

≡

72

Property Axioms (2)


OWL allows the definition of property characteristics to infer new facts relating to instances and their properties

• Symmetry

• Transitivity

• Inverse

• Functional

• Inverse Functional

73

Property Axioms: Symmetry



dbpedia: Billy_Preston

dbpedia: Plastic_Ono_

Band :associatedMusicalArtist a owl:SymmetricProperty .

?genre

dbpedia:Plastic_Ono_Band

?genre

dbpedia:Plastic_Ono_Band

dbpedia:Billy_Preston

:associatedMusicalArtist

Schema:


SELECT ?x WHERE { dbpedia:The_Beatles :associatedMusicalArtist ?x.}

Query:

:associatedMusicalArtist

74

Property Axioms: Transitivity


:Rock

:Heavy_ metal

:Black_ metal

:Punk_ rock SELECT ?genre WHERE {

:Rock :subgenre ?genre .}

:subgenre a owl:TransitiveProperty .

?genre

:Heavy_metal

:Punk_rock

?genre

:Heavy_metal

:Punk_rock

:Black_metal

:subgenre :subgenre

:subgenre :subgenre

Schema:

Query:


75

Property Axioms: Inverse


SELECT ?x WHERE { ?x mo:member_of dbpedia:The_Beatles .}

mo:member_of owl:inverseOf mo:member.

?x

dbpedia:John_Lennon


?x

dbpedia:John_Lennon



dbpedia:Ringo_Starr

Schema:

Query:




mo:member_of




mo:member

mo:member_of

mo:member

mo:member_of mo:member_of

76

Example: Every artist primarily plays only one musical instrument

mo:primary_instrument rdf:type owl:FunctionalProperty .

dbpedia:Jimi_Hendrix mo:primary_instrument dbpedia:Electric_Guitar.dbpedia:Jimi_Hendrix mo:primary_instrument dbpedia:E-Guitar.

Conclusion dbpedia:Electric_Guitar

owl:sameAs dbpedia:E-Guitar .

Property Axioms:Functional


It refers to a property that can have only one (unique) value for each instance

r2

mo:primary_

instrument

same

r1

mo:primary_ instrument

77

Example: Every recording has a unique ISRC(International Standard Recording Code)

mo:isrc rdf:type owl:InverseFunctionalProperty .

mo:21047249-7b3f-4651-acca-246669c081fd mo:isrc "GBAYE6300412" .dbpedia:She_Loves_You mo:isrc "GBAYE6300412" .

Conclusion mo:21047249-7b3f-4651-acca-246669c081fd

owl:sameAs :dbpedia:She_Loves_You .

Property Axioms:Inverse Functional


It is useful for specifying unique properties identifying an individual

r2

mo:isrc

mo:isrcsam

e

r1

78

Individual Axioms


OWL Individuals represent instances of classes. They are related to their class by the rdf:type property

• We can state that two individuals are the same SameIndividual(<artist/ba550d0e-adac-4864-b88b-407cab5e76af#_> dbpedia:PaulMcCartney)

<artist/ba550d0e-adac-4864-b88b-407cab5e76af#_> owl:sameAs dbpedia:PaulMcCartney .

• We can state that two individuals are different DifferentIndividuals(:TheBeatles_band :TheBeatles_TVseries)

:TheBeatles_band owl:differentFrom :TheBeatles_Tvseries .

≡

≡

79

Class Axioms


Axioms declare general statements about concepts which are used in logical inference (reasoning). Class axioms:

• Sub-class relationship (from RDF Schema)

• Equivalent relationship: classes have the same individuals EquivalentClass(:Musician :MusicArtist)

:Musician owl:equivalentClass :MusicArtist .

• Disjointness: classes have no shared individuals DisjointClasses(:SoloMusicArtist :MusicGroup)

:SoloMusicArtist owl:disjointWith :MusicGroup .≡

≡

80

Class Construction


• OWL classes are defined by the OWL term owl:Class

• OWL classes can be subclassed as in RDFS:

• OWL classes may be combined with class constructs to build new classes

Music Artist

Artist:MusicArtist rdfs:subClassOf :Artist .

Class Construction (2)

EUCLID - Querying Linked Data 81

These class constructs are available in OWL, not in RDFS The class of female music artists ObjectIntersectionOf(:Female :MusicArtist) [a owl:Class; owl:intersectionOf(:Female :MusicArtist)]

The class of music artists ObjectUnionOf(:SoloMusicArtist :MusicGroup) [a owl:Class; owl:unionOf(:SoloMusicArtist :MusicGroup)]

Everything that’s not instrumental music ObjectComplementOf(:InstrumentalMusic) [a owl:Class; owl:complementOf(:InstrumentalMusic)]

Female

Music Artist

Solo

Group

Instrumental

≡

≡

≡NOTE: Anonymous classes!

82

Naming Class Constructions


• Direct naming can be achieved via owl:equivalentClass

• This construction provides necessary and sufficient conditions for class membership

• Class naming can be also achieved using rdfs:subClassOf, it provides a necessary but insufficient condition for class membership

Music ArtistSolo

Group

EquivalentClass(:MusicArtist ObjectUnionOf(:SoloMusicArtist :MusicGroup))

:MusicArtist owl:equivalentClass [owl:unionOf (:SoloMusicArtist :MusicGroup)]

≡

83

Summary


• Basic concepts: triple patterns, graph patterns, SPARQL endpoint ...

• SPARQL Query:

• Query forms: ASK, SELECT, DESCRIBE, CONSTRUCT

• Query patterns: BGP, UNION, OPTIONAL, FILTER

• Sequence modifiers: DISTINCT, REDUCED, ORDER BY, LIMIT, OFFSET

• SPARQL 1.1 Update:

• Data management: INSERT, DELETE; DELETE/INSERT

• Graph management: LOAD, CLEAR, CREATE, DROP, COPY/MOVE/ADD

• SPARQL Protocol: query operation, update operation

Qu

ery

ing

Lin

ked

Data

In this chapter we studied:

84

Summary (2)


• Reasoning over Linked Data:

• SPARQL 1.1 entailment regimes

• RDFS: entailment regimes, lacks of consistency check, inference limitations

• OWL: properties, property axioms (symmetry, transitivity, inverse, functional, inverse functional), individual axioms, class axioms, class constructions, naming classes …

Reason

ing

over

Lin

ked

DataIn this chapter we studied:

EUCLID - Providing Linked Data 85

For exercises, quiz and further material visit our website:

@euclid_project euclidproject euclidproject

http://www.euclid-project.eu

Other channels:

eBook Course

86

Acknowledgements

• Alexander Mikroyannidis• Alice Carpentier• Andreas Harth• Andreas Wagner• Andriy Nikolov• Barry Norton• Daniel M. Herzig• Elena Simperl• Günter Ladwig• Inga Shamkhalov• Jacek Kopecky• John Domingue

• Juan Sequeda• Kalina Bontcheva• Maria Maleshkova• Maria-Esther Vidal• Maribel Acosta• Michael Meier• Ning Li• Paul Mulholland• Peter Haase• Richard Power• Steffen Stadtmüller

People who have contributed to creating Euclid training content:

querying linked data

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