Querying Trust
in RDF Data with
tSPARQL
Olaf Hartig
http://olafhartig.de/foaf.rdf#olaf

● The Semantic Web is a reality
● Large amount of semantically interlinked data
● Applications emerge
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 2

Is the data
trustworthy?
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 3

SELECT ?hotel ?hotelName
WHERE {
?hotel rdf:type umbel:HotelBuilding ;
p:location dbpedia:Heraklion ;
rdfs:label ?hotelName .
TRUST AS ?t
}
ORDER BY ?t
Returns a list of hotels
in Heraklion ordered by the
trustworthiness of the data.
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 4

SELECT ?hotelName ?reviewText
WHERE {
?hotel rdf:type umbel:HotelBuilding ;
p:location dbpedia:Heraklion ;
rdfs:label ?hotelName .
{
?hotel rev:hasReview ?review .
?review rev:text ?reviewText .
SELECT ?hENSURE TRUST ( 0.7 , 1.0 )
?name WHERE {
?h rdf:type umbel:HotelBuilding ;
}
p:location dbpedia:Heraklion ;
} rdfs:label ?name .
TRUST AS ?t
}
ORDER BY ?t
Returns trustworthy reviews
of hotels in Heraklion.
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 5

Outline
Trust model
for RDF data
Trust-aware
tSPARQL query processing
Evaluating trust
requirements
Query optimization
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 6

Trustworthiness of RDF Data
● The trustworthiness of RDF statements is the subjective
belief or disbelief in the truth of the statements.
● Represented by trust values in the interval [-1,1]
rdfs:label
<http://.../data/KnossosRoyal> Aldemar Knossos Royal Village
ex:
loc
rd
ate
f:t
d At t 5.5378
geo:la
yp
e
geo:l
umbel:HotelBuilding ong
−0.2274
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 7

Atomic Trust
● A trust function associates single RDF statements with a
subjective trust value.
<http://.../data/KnossosRoyal>
TrustFct ( , ) = 0.8
rd
f:t
yp
e
umbel:HotelBuilding
Trust weighted statement • Trust weighted RDF graph
rdfs:label
<http://.../data/KnossosRoyal> Aldemar Knossos Royal Village
[0.9]
ex: [0.1]
loc
rd
ate [0.75]
f:t
[0.8] dA t 5.5378
t geo:la
yp
e
geo:l
umbel:HotelBuilding ong
−0.2274
[0.75]
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 8

Aggregated Trust
● A trust aggregation function calculates an aggregated
trust value for a trust weighted RDF graph.
● Minimum (cautious): tamin = 0.1
● Median (more optimistic):
tamedian = 0.75
rdfs:label
<http://.../data/KnossosRoyal> Aldemar Knossos Royal Village
[0.9]
ex: [0.1]
loc
rd
ate [0.75]
f:t
[0.8] dA t 5.5378
t geo:la
yp
e
geo:l
umbel:HotelBuilding ong
−0.2274
[0.75]
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 9

Outline
Trust model
for RDF data
Trust-aware
tSPARQL query processing
Evaluating trust
requirements
Query optimization
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 10

Trust-aware query processing
● SPARQL does not consider trust values
● Basic idea:
● Extend the notion of solutions
● Redefine the algebra operators
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 11

Basic graph pattern matching
<http://.../data/KnossosRoyal> rev:hasReview
<http://revyu.../R457>
re v
rd
:ha rev
sR :tex
f:t
e vie t
yp
w
e
What a lovely ...
umbel:HotelBuilding <http://revyu.../R337>
rev:te
xt A surprisingly ...
BGP
<http://.../data/KnossosRoyal> rev:hasReview
?r
rev:text ?t
µ
Solution mappings ?r ?t
that are solutions: http://revyu.../R457 \"What a lovely ...\"
http://revyu.../R337 \"A surprisingly ...\"
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 12

Basic graph pattern matching
<http://.../data/KnossosRoyal> rev:hasReview
<http://revyu.../R457>
re v
rd
:ha rev
sR :tex
f:t
e vie t
yp
w
e
What a lovely ...
umbel:HotelBuilding <http://revyu.../R337>
rev:te
xt A surprisingly ...
BGP
<http://.../data/KnossosRoyal> rev:hasReview
?r
rev:text ?t
µ
Solution mappings ?r ?t
that are solutions: http://revyu.../R457 \"What a lovely ...\"
http://revyu.../R337 \"A surprisingly ...\"
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 13

Basic graph pattern matching
<http://.../data/KnossosRoyal> rev:hasReview
<http://revyu.../R457>
re v [0.86]
rd
:ha rev
sR [0.86] :tex [0.7]
f:t
[0.8] evi t
yp
ew
e
What a lovely ...
umbel:HotelBuilding <http://revyu.../R337> [0.2]
rev:te
xt A surprisingly ...
BGP
<http://.../data/KnossosRoyal> rev:hasReview
?r
rev:text ?t
Trust weighted µ t
solution mappings ?r ?t
that are solutions: http://revyu.../R457 \"What a lovely ...\"
http://revyu.../R337 \"A surprisingly ...\"
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 14

Basic graph pattern matching
<http://.../data/KnossosRoyal> rev:hasReview
<http://revyu.../R457>
re v [0.86]
rd
:ha rev
sR [0.86] :tex [0.7]
f:t
[0.8] evi t
yp
ew
e
What a lovely ...
umbel:HotelBuilding <http://revyu.../R337> [0.2]
rev:te
xt A surprisingly ...
BGP
<http://.../data/KnossosRoyal> rev:hasReview
?r
rev:text ?t
Trust weighted µ t
solution mappings ?r ?t
that are solutions: http://revyu.../R457 \"What a lovely ...\"
http://revyu.../R337 \"A surprisingly ...\"
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 15

Basic graph pattern matching
<http://.../data/KnossosRoyal> rev:hasReview
<http://revyu.../R457>
rev [0.86]
rd
:ha re v
s Re[0.86] :tex [0.7]
f:t
[0.8] v t
yp
iew
e
What a lovely ...
umbel:HotelBuilding <http://revyu.../R337> [0.2]
rev:te
xt A surprisingly ...
BGP
<http://.../data/KnossosRoyal> rev:hasReview
?r
rev:text ?t
Trust weighted µ t
solution mappings ?r ?t
that are solutions: http://revyu.../R457 \"What a lovely ...\" 0.7
http://revyu.../R337 \"A surprisingly ...\"
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 16

Basic graph pattern matching
<http://.../data/KnossosRoyal> rev:hasReview
<http://revyu.../R457>
re v [0.86]
rd
:ha rev
sR [0.86] :tex [0.7]
f:t
[0.8] evi t
yp
ew
e
What a lovely ...
umbel:HotelBuilding <http://revyu.../R337> [0.2]
rev:te
xt A surprisingly ...
BGP
<http://.../data/KnossosRoyal> rev:hasReview
?r
rev:text ?t
Trust weighted µ t
solution mappings ?r ?t
that are solutions: http://revyu.../R457 \"What a lovely ...\" 0.7
http://revyu.../R337 \"A surprisingly ...\" 0.2
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 17

Trust-aware query processing
● SPARQL does not consider trust values
Basic idea:
√
●
● Extend the notion of solutions
● Redefine the algebra operators
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 18

Redefining the SPARQL algebra
{
{
?h rdf:type umbel:HotelBuilding ;
p:location dbpedia:Heraklion .
}
{
?h rev:hasReview [ rev:text ?txt1 ]
}
} Join
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 19

Redefining the SPARQL algebra
µ
?h ?r
ex:KnossosRoyal \"What a lovely …\"
ex:KnossosRoyal \"A surprisingly …\"
ex:SheratonTenerife \"Located direct...\"
Join
µ
µ
?h ?r
?h
ex:KnossosRoyal \"What a lovely …\"
ex:KnossosRoyal ex:KnossosRoyal \"A surprisingly …\"
ex:SheratonTenerife ex:SheratonTenerife \"Located direct...\"
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 20

Redefining the SPARQL algebra
µ t
?h ?r
ex:KnossosRoyal \"What a lovely …\"
ex:KnossosRoyal \"A surprisingly …\"
ex:SheratonTenerife \"Located direct...\"
Join
µ t
µ t
?h ?r
?h
ex:KnossosRoyal \"What a lovely …\" 0.9
ex:KnossosRoyal 0.7 ex:KnossosRoyal \"A surprisingly …\" 0.2
ex:SheratonTenerife 0.1 ex:SheratonTenerife \"Located direct...\" 0.8
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 21

Redefining the SPARQL algebra
● A trust merge function calculates a merged trust value for
two trust weighted solution mappings.
µ t
● Minimum: tmmin
?h ?r
ex:KnossosRoyal \"What a lovely …\" 0.7
ex:KnossosRoyal \"A surprisingly …\" 0.2
ex:SheratonTenerife \"Located direct...\" 0.1
Join
µ t
µ t
?h ?r
?h
ex:KnossosRoyal \"What a lovely …\" 0.9
ex:KnossosRoyal 0.7 ex:KnossosRoyal \"A surprisingly …\" 0.2
ex:SheratonTenerife 0.1 ex:SheratonTenerife \"Located direct...\" 0.8
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 22

Basic idea
● SPARQL does not consider trust values
Basic idea:
√
●
● Extend the notion of solutions
● Redefine the algebra operators √
What is the impact of
processing trust values
on query execution times
?
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 23

Evaluation
● tSPARQL query engine (extension of SPARQL engine ARQ)
● Berlin SPARQL Benchmark (BSBM)
● Simulates e-commerce scenario
● Mix of 12 SPARQL queries
● Generates datasets of different sizes (scaling factor)
3
avg. execution time
(in sec.) per query mix
ARQ SPARQL tSPARQL engine
2,5 engine with
2 precomputed
trust values
1,5
1
0,5
0
0 100 (31800) 200 (60424) 300 (92337) 400 (124305) 500
BSBM Scaling Factor (# of triples)
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 24

Evaluation
● Simple provenance-based trust function
● Assumes existence of trust assessments for RDF graphs
● Adopts these trust values for all triples in the graph
ARQ SPARQL tSPARQL engine tSPARQL engine
avg. execution time (in sec.)
per query mix
engine with + determining
precomputed trust values
trust values
10
8
6
4
2
0
0 100 (31800) 200 (60424) 300 (92337) 400 (124305) 500
BSBM Scaling Factor (# of triples)
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 25

Outline
Trust model
for RDF data
Trust-aware
tSPARQL query processing
Evaluating trust
requirements
Query optimization
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 26

Evaluating trust requirements
● Goal: ensuring a certain trustworthiness for the solutions
of a specific graph pattern
SELECT ?hotelName ?reviewText
WHERE {
?hotel rdf:type umbel:HotelBuilding ;
p:location dbpedia:Heraklion ;
rdfs:label ?hotelName .
{
?hotel rev:hasReview ?review .
?review rev:text ?reviewText .
ENSURE TRUST ( 0.7 , 1.0 )
}
}
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 27

Evaluating trust requirements
● Goal: ensuring a certain trustworthiness for the solutions
of a specific graph pattern
µ t
?h ?r
ex:KnossosRoyal \"What a lovely …\" 0.9
ex:SheratonTenerife \"Located direct...\" 0.8
EnTrust
0.5 , 1.0
µ t
?h ?r
ex:KnossosRoyal \"What a lovely …\" 0.9
ex:KnossosRoyal \"A surprisingly …\" 0.2
ex:SheratonTenerife \"Located direct...\" 0.8
EnTrust l , u ,  = {  , t  ∣ , t ∈ ∧ lt u }
* *
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 28

Evaluating trust requirements
Join
{
{ ?h rdf:type umbel:HotelBuilding ;
p:location dbpedia:Heraklion . }
{ ?h rev:hasReview [ rev:text ?txt1 ]
ENSURE TRUST ( 0.5 , 1.0 ) }
} EnTrust
0.5 , 1.0
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 29

Evaluating trust requirements
Join
{
{ ?h rdf:type umbel:HotelBuilding ;
p:location dbpedia:Heraklion . }
{ ?h rev:hasReview [ rev:text ?txt1 ]
ENSURE TRUST ( 0.5 , 1.0 ) }
} EnTrust
0.5 , 1.0
µ t
µ t
?h ?r
?h
ex:KnossosRoyal \"What a lovely …\" 0.9
ex:KnossosRoyal 0.7 ex:KnossosRoyal \"A surprisingly …\" 0.2
ex:SheratonTenerife 0.1 ex:SheratonTenerife \"Located direct...\" 0.8
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 30

Evaluating trust requirementsµ t
?h ?r
ex:KnossosRoyal \"What a lovely …\" 0.7
ex:SheratonTenerife \"Located direct...\" 0.8
Join
{ µ t
{ ?h rdf:type umbel:HotelBuilding ;
?h ?r
p:location dbpedia:Heraklion . }
ex:KnossosRoyal
{ ?h rev:hasReview [ rev:text ?txt1 ] \"What a lovely …\" 0.9
ENSURE TRUST ( 0.5 , 1.0 ) }ex:SheratonTenerife \"Located direct...\" 0.8
} EnTrust
0.5 , 1.0
µ t
µ t
?h ?r
?h
ex:KnossosRoyal \"What a lovely …\" 0.9
ex:KnossosRoyal 0.7 ex:KnossosRoyal \"A surprisingly …\" 0.2
ex:SheratonTenerife 0.1 ex:SheratonTenerife \"Located direct...\" 0.8
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 31

Evaluating trust requirementsµ t
?h ?r
ex:KnossosRoyal \"What a lovely …\" 0.7
ex:SheratonTenerife \"Located direct...\" 0.8
EnTrust
0.5 , 1.0
{
{ ?h rdf:type umbel:HotelBuilding ;
p:location dbpedia:Heraklion . }
{ ?h rev:hasReview [ rev:text ?txt1 ]
ENSURE TRUST ( 0.5 , 1.0 ) }
ENSURE TRUST ( 0.5 , 1.0 )
}
Join
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 32

Evaluating trust requirementsµ t
?h ?r
ex:KnossosRoyal \"What a lovely …\" 0.7
ex:SheratonTenerife \"Located direct...\" 0.8
EnTrust
0.5 , 1.0
{
{ ?h rdf:type umbel:HotelBuilding ;
p:location dbpedia:Heraklion . }
{ ?h rev:hasReview [ rev:text ?txt1 ]
ENSURE TRUST ( 0.5 , 1.0 ) }
ENSURE TRUST ( 0.5 , 1.0 )
}
Join
µ t
µ t
?h ?r
?h
ex:KnossosRoyal \"What a lovely …\" 0.9
ex:KnossosRoyal 0.7 ex:KnossosRoyal \"A surprisingly …\" 0.2
ex:SheratonTenerife 0.1 ex:SheratonTenerife \"Located direct...\" 0.8
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 33

Evaluating trust requirementsµ
µ t t
?h ?r ?h ?r
ex:KnossosRoyal \"What a lovely …\" 0.7 ex:KnossosRoyal \"What a lovely …\" 0.7
ex:SheratonTenerife \"Located direct...\" 0.8
EnTrust
0.5 , 1.0
{
{ ?h rdf:type umbel:HotelBuilding ; µ t
p:location dbpedia:Heraklion . ?h } ?r
{ ?h rev:hasReview [ rev:text ?txt1 ]
ex:KnossosRoyal \"What a lovely …\" 0.7
ENSURE TRUST ( 0.5 , 1.0 ) }ex:KnossosRoyal \"A surprisingly …\" 0.2
ENSURE TRUST ( 0.5 , 1.0 ) ex:SheratonTenerife \"Located direct...\" 0.1
}
Join
µ t
µ t
?h ?r
?h
ex:KnossosRoyal \"What a lovely …\" 0.9
ex:KnossosRoyal 0.7 ex:KnossosRoyal \"A surprisingly …\" 0.2
ex:SheratonTenerife 0.1 ex:SheratonTenerife \"Located direct...\" 0.8
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 34

Evaluating trust requirementsµ
µ t t
?h ?r ?h ?r
ex:KnossosRoyal \"What a lovely …\" 0.7 ex:KnossosRoyal \"What a lovely …\" 0.7
ex:SheratonTenerife \"Located direct...\" 0.8
EnTrust
0.5 , 1.0
● Position of the µ t
ENSURE TRUST ?h ?r
clause matters! ex:KnossosRoyal \"What a lovely …\" 0.7
ex:KnossosRoyal \"A surprisingly …\" 0.2
ex:SheratonTenerife \"Located direct...\" 0.1
Join
µ t
µ t
?h ?r
?h
ex:KnossosRoyal \"What a lovely …\" 0.7
ex:KnossosRoyal 0.9 ex:KnossosRoyal \"A surprisingly …\" 0.2
ex:SheratonTenerife 0.1 ex:SheratonTenerife \"Located direct...\" 0.8
BGP BGP
?h rdf:type umbel:HotelBuilding . ?h rev:hasReview [ rev:text ?r ]
?h p:location dbpedia:Heraklion .
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 35

Accessing trust values
● Goal: accessing the trust value for the solution of a
specific graph pattern
SELECT ?hotel ?hotelName
WHERE {
?hotel rdf:type umbel:HotelBuilding ;
p:location dbpedia:Heraklion ;
rdfs:label ?hotelName .
TRUST AS ?t
}
ORDER BY ?t
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 36

Accessing trust values
● Goal: accessing the trust value for the solution of a
specific graph pattern
● Again: position of the
µ t
TRUST AS clause
?h ?r ?t
matters! ex:KnossosRoyal \"What a lovely …\" 0.9 0.9
ex:SheratonTenerife \"Located direct...\" 0.8 0.8
PrTrust
?t
µ t
?h ?r
ex:KnossosRoyal \"What a lovely …\" 0.9
ex:SheratonTenerife \"Located direct...\" 0.8
PrTrust v , * = {  ' , t  ∣  , t ∈* ∧  '=∪{  v , lt   } }
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 37

Outline
Trust model
for RDF data
Trust-aware
tSPARQL query processing
Evaluating trust
requirements
Query optimization
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 38

Rewrite Rules
● Rewriting algebra expressions to improve query execution
● E.g., for join operators that employ
the trust merge function tmmin holds:
EnTrust EnTrust
l,u l,u
Join Equivalence Join
EnTrust EnTrust
l , 1.0 l , 1.0
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 39

Evaluation
● Equivalent BSBM-based setup with 6 tSPARQL queries
100
avg. exec.time (in sec.) per query mix
tSPARQL engine tSPARQL engine
90 without rewriting with rewriting
80
70
60
50
40
30
20
10
0
0 100 (31800) 200 (60424) 300 (92337) 400 (124305) 500
BSBM Scaling Factor (# of triples)
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 40

Take-away summary
Trust model
for RDF data
● Trust model
● Trust function tSPARQL
Trust-aware
query processing
● Trust aggregation function Evaluating trust
requirements
● Trust in SPARQL query processing Query optimization
● Trust weighted solutions
● Trust-aware algebra
● SPARQL extension for trust requirements
● ENSURE TRUST
● TRUST AS
● tSPARQL query engine available: http://trdf.sourceforge.net
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 41

These slides have been created by
Olaf Hartig
http://olafhartig.de
This work is licensed under a
Creative Commons Attribution-Share Alike 3.0 License
(http://creativecommons.org/licenses/by-sa/3.0/)
Olaf Hartig - Querying Trust in RDF Data with tSPARQL 42