Querying Linked Data

Querying Linked Data
Presented by:
Barry Norton

Motivation: Music!
2
Visualization
Module
Metadata
Streaming providers
Physical Wrapper
Downloads
Dataacquisition
D2R Transf.LD Wrapper
Musical Content
Application
Analysis &
Mining Module
LDDatasetAccess
LD Wrapper
RDF/
XML
Integrated
Dataset
Interlinking Cleansing
Vocabulary
Mapping
SPARQL
Endpoint
Publishing
RDFa
Other content

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
3EUCLID - Querying Linked Data

INTRODUCTIONTO SPARQL
EUCLID - Querying Linked Data 4

SPARQL
Semantic Web Stack
Berners-Lee (2006)
* Protocol and RDF Query Language
Declarative query language

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/

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, A
dd
• Aggregates, Subqueries, Negation, E
xpressions 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

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.}

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

QUERYING LINKED DATA WITH
SPARQL

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

SPARQL Query
?album
dbpedia:
The_Beatles
foaf:made
dbpedia:
The_Beatlesfoaf:made
<http://
musicbrainz.org
/record/...>
<http://
musicbrainz.org
/record/...>
foaf:made
Data:
Graph pattern:
Results:
"Help!" "Let It Be"
dc:title dc:title
<http://
musicbrainz.org
/record/...>
"Abbey Road"
dc:title
foaf:made
?album
<http://musicbrainz.org...>

SPARQL Query
?album
dbpedia:
The_Beatles
dbpedia:
<http://
musicbrainz.org
/record/...>
<http://
musicbrainz.org
/record/...>
foaf:made
Data:
Graph pattern:
Results:
"Help!" "Let It Be"
dc:title dc:title
<http://
musicbrainz.org
/record/...>
"Abbey Road"
dc:title
foaf:made
?album ?title
<http://...> "Help!"
<http://...> "Abbey Road"
<http://...> "Let It Be"
?title
dc:title

SPARQL Query
?album
dbpedia:
The_Beatles
dbpedia:
<http://
musicbrainz.org
/record/...>
<http://
musicbrainz.org
/track/...>
foaf:made
Data:
Graph pattern:
Results:
"Help!" "Help!"
dc:title dc:title
mo:track
a
mo:Record mo:Track
mo:Record
?album

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 ?album
FROM <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

Query form:
• ASK, SELECT, DESCRIBE or CONSTRUCT
• SELECT retrieves variables and their bindings as a table
SELECT ?album
WHERE {
}
ORDER BY ?title

Data set specification:
• This clause is optional
• FROM or FROM NAMED
• Indicates the sources for the data against which to find matches
SELECT ?album
WHERE {
}
ORDER BY ?title

Query pattern:
• Defines patterns to match against the data
• Generalises Turtle with variables and keywords – N.B. final period optional
SELECT ?album
WHERE {
}
ORDER BY ?title

Solution modifier:
• Modify the result set
• ORDER BY, LIMIT or OFFSET re-organise rows;
• GROUP BY combines them
SELECT ?album
WHERE {
}
ORDER BY ?title

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

Query Form: ASK
• Namespaces are added with the ‘PREFIX’ directive
• Statement patterns that make up the graph are
specified between brackets (“{}”)
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 mo: http://purl.org/ontology/mo/
ASK WHERE { dbpedia:The_Beatles mo:member
dbpedia:Elvis_Presley.}

Query Form: SELECT
• The solution modifier projection nominates which
components of the matches should be returned
• “*” means all components should be returned
SELECT ?album_name ?track_title
WHERE {
?album dc:title ?album_name ;
mo:track ?track .
?track dc:title ?track_title .}
Query: What albums and tracks did ‘The Beatles’ make?

Filter expressions
• Different types of filters and functions may be used
Query Form: SELECT (2)
SELECT ?album_name ?track_title ?date ?duration
WHERE {
mo:track ?track .
?track dc:title ?track_title ;
mo:duration ?duration;
FILTER (?duration>300000 && ?duration<400000) }
Query:
Filter: Comparison and logical operators
Retrieve 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.

Elimination of duplicates
SELECT MODIFIER ?album_name
WHERE {
?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:
REDUCED
MODIFIER= MODIFIER=

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
SELECT ?album (SUM(?track_duration) AS ?album_duration)
WHERE {
?track mo:duration ?track_duration .
} GROUP BY ?album
HAVING (SUM(?track_duration) > 3600000)
Retrieve the duration of the albums recorded by ‘The Beatles’.Query:

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
DESCRIBE ?member
WHERE {
dbpedia:The_Beatles mo:member ?member .}
DESCRIBE dbpedia:Paul_McCartney

• CONSTRUCT WHERE: In order to query for a
subgraph, without change, it is no longer necessary
to repeat the graph pattern in the template
CONSTRUCT WHERE {
?album mo:track ?track .}
Example:
Query Form: CONSTRUCT

Query Form: CONSTRUCT (2a)
dbpedia:
<http://
musicbrainz.org
/record/...>
<http://
musicbrainz.org
/record/...>
foaf:made
Data:
Query: Result:
"Help!" "Let It Be"
dc:title dc:title
<http://
musicbrainz.org
/record/...>
"Abbey Road"
dc:title
foaf:made
CONSTRUCT {
?album dc:creator dbpedia:The_Beatles .}
WHERE {
dbpedia:The_Beatles foaf:made ?album .}
dbpedia:
The_Beatles
<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
CONSTRUCT {
?album dc:creator dbpedia:The_Beatles .
?track dc:creator dbpedia:The_Beatles .}
WHERE {
?album mo:track ?track .}
Create the dc:creator descriptions for albums and their tracks
recorded by ‘The Beatles’.Query:
Query Form: CONSTRUCT (2b)

Query Form: CONSTRUCT (3)
Subsets of results
• It is possible to combine the query with solution modifiers
(ORDER BY, LIMIT, OFFSET)
CONSTRUCT {
WHERE {
?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:

Union Graph Pattern
• Allows the specification of alternatives (disjunctions)
PREFIX foaf: http://xmlns.com/foaf/0.1/
CONSTRUCT {
WHERE {
?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:

Filter expressions
• Different types of filters and functions may be used
CONSTRUCT {?album dc:creator dbpedia:The_Beatles .}
WHERE {
FILTER (REGEX(?album_name, ".*love.*", i)) }
Query:
Filter: Regular expressions over strings
Create the dc:creator descriptions of the albums recorded by
‘The Beatles’ whose title contains the word ‘love .

Type of function Function Result type
Functional Forms
bound
IF
COALESCE
NOT EXISTS, EXISTS
or, and
RDFTerm-equal (=), sameTerm
IN, NOT IN
xsd:boolean
rdfTerm
rdfTerm
xsd:boolean
xsd:boolean
xsd:boolean
boolean
Functions on RDF Terms
isIRI, isBlank, isLiteral, isNumeric
str, lang,
datatype
IRI
BNODE
xsd:boolean
simple literal
iri
iri
blank node
Functions on Numerics ABS, ROUND, CEIL, FLOOR
RAND
numeric
xsd:double
Filter expressions
Source:http://www.w3.org/TR/sparql11-query/#SparqlOps

Type of function Function Result type
Functions on Strings STRLEN
SUBSTR, UCASE, LCASE
STRSTARTS, STRENDS, CONTAINS
STRBEFORE, STRAFTER
ENCODE_FOR_URI
CONCAT
langMatches
REGEX
REPLACE
xsd:integer
string literal
xsd:boolean
literal
simple literal
string literal
xsd:boolean
xsd:boolean
string literal
Functions on Dates and
Times
now
year, month, day, hours, minutes
seconds
timezone
tz
xsd:dateTime
xsd:integer
xsd:decimal
xsd:dayTimeDuration
simple literal
Filter expressions
Source:http://www.w3.org/TR/sparql11-query/#SparqlOps

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 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:

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 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 .}

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
CONSTRUCT { ?track dbpedia-ont:runtime ?secs .}
WHERE {
?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:

Sub-queries and Aggregate Values
• To combine the CONSTRUCT query form with aggregate values, a
sub-query should be created inside the WHERE clause
CONSTRUCT {?album music-ont:duration ?album_duration .}
WHERE {
SELECT ?album (SUM(?track_duration) AS ?album_duration) {
?track mo:duration ?track_duration .
} GROUP BY ?album
HAVING (SUM(?track_duration) > 3600000)}
Materialize the duration of the albums recorded by ‘The Beatles’.Query:

UPDATING LINKED DATA WITH
SPARQL 1.1

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

Data Management (2)
INSERT data
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 byThe Beatles into the graph
http://musicbrainz.org/20130209-004702
CH 1

Data Management (3)
DELETE data
Delete all the information about the album Casualities of The Beatles.
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

Data Management (4)
DELETE/INSERT data
PREFIX db-ont: <http://dbpedia.org/ontology/>
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.

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

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

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>

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

SPARQL PROTOCOL FOR RDF

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 Endpoint
Request
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:
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)

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

REASONING OVER LINKED DATA

Reasoning for
Linked Data Integration
• Example: Integration of the MusicBrainz data set and
the DBpedia data set
Integration
Data set Data set

Reasoning for
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 .
Integration
Data set Data set
same

Reasoning for
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:

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 entailment
Source: http://www.w3.org/TR/rdf-mt/#RDFSRules

RDFS
Resource Description Framework Schema
Semantic Web Stack
Berners-Lee (2006)
Taxonomies and inferences

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

rdfs2 – rdfs:domain
dbpedia:
The_Beatles
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

rdfs3 – rdfs:range
dbpedia:
The_Beatles
dbpedia:
Paul_McCartney
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:
dbpedia:
John_Lennon
dbpedia:
George_Harrison
dbpedia:
Ringo_Starr
dbpedia-ont:
bandMember
dbpedia-ont:
bandMember
dbpedia-ont:
bandMember

rdfs7 – rdfs:subPropertyOf
dbpedia:
Yesterday
dbpedia:
Paul_McCartney
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:
dbpedia:
John_Lennon
dbpedia:
George_Harrison
dbpedia:
Ringo_Starr
mo:performer mo:performermo:performer
mo:performer

rdfs9 – rdfs:subClassOf
dbpedia:
The_Beatles
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

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 .

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

• 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
inferred:
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’

OWL
Web Ontology Language
Semantic Web Stack
Berners-Lee (2006)
Ontologies and inferences

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

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 .

PropertyAxioms
• 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.
≡
dbpedia:
The_Beatles
dbpedia:
Paul_McCartney
mo:member
dbpedia:
John_Lennon
dbpedia:
George_Harrison
dbpedia:
Ringo_Starr
mo:member
mo:member
mo:member
SELECT ?x {dbpedia:The_Beatles
dbpedia-ont:bandMember ?x.}
Query:
?x
Result set:
?x
dbpedia:John_Lennon
dbpedia:Ringo_Starr
Result set with inference:

PropertyAxioms
• 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
≡
≡

PropertyAxioms (2)
OWL allows the definition of property characteristics to infer new
facts relating to instances and their properties
• Symmetry
• Transitivity
• Inverse
• Functional
• Inverse Functional

Property Axioms:
Symmetry
dbpedia:
The_Beatles
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

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:

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:
dbpedia:
The_Beatles
dbpedia:
Paul_McCartney
mo:member_of
dbpedia:
John_Lennon
dbpedia:
George_Harrison
dbpedia:
Ringo_Starr
mo:member
mo:member_of
mo:member
mo:member_of mo:member_of

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
same
r1

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
same
r1

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 .
≡
≡

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 .
≡
≡

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)
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!

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 Artist
Solo
Group
EquivalentClass(:MusicArtist
ObjectUnionOf(:SoloMusicArtist
:MusicGroup))
:MusicArtist owl:equivalentClass
[owl:unionOf (:SoloMusicArtist :MusicGroup)]
≡

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
QueryingLinkedData
In this chapter we studied:

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 …
ReasoningoverLinkedData
In this chapter we studied:

For exercises, quiz and further material visit our website:
EUCLID - Providing Linked Data 85
@euclid_project euclidproject euclidproject
http://www.euclid-project.eu
Other channels:
eBook Course

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
86

Querying Linked Data

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