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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        quot;What a lovely ...quot;
                                                        http://revyu.../R337        quot;A surprisingly ...quot;
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        quot;What a lovely ...quot;
                                                        http://revyu.../R337        quot;A surprisingly ...quot;
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        quot;What a lovely ...quot;
                                                          http://revyu.../R337        quot;A surprisingly ...quot;
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        quot;What a lovely ...quot;
                                                          http://revyu.../R337        quot;A surprisingly ...quot;
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        quot;What a lovely ...quot;     0.7
                                                          http://revyu.../R337        quot;A surprisingly ...quot;
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        quot;What a lovely ...quot;     0.7
                                                          http://revyu.../R337        quot;A surprisingly ...quot;    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     quot;What a lovely …quot;
                                                               ex:KnossosRoyal     quot;A surprisingly …quot;
                                                               ex:SheratonTenerife quot;Located direct...quot;

                                                        Join

                                                                                 µ
              µ
                                                                       ?h                  ?r
             ?h
                                                               ex:KnossosRoyal     quot;What a lovely …quot;
 ex:KnossosRoyal                                               ex:KnossosRoyal     quot;A surprisingly …quot;
 ex:SheratonTenerife                                           ex:SheratonTenerife quot;Located direct...quot;
                             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     quot;What a lovely …quot;
                                                               ex:KnossosRoyal     quot;A surprisingly …quot;
                                                               ex:SheratonTenerife quot;Located direct...quot;

                                                        Join

                                                                                  µ                      t
              µ                  t
                                                                       ?h                  ?r
             ?h
                                                               ex:KnossosRoyal     quot;What a lovely …quot; 0.9
 ex:KnossosRoyal               0.7                             ex:KnossosRoyal     quot;A surprisingly …quot; 0.2
 ex:SheratonTenerife           0.1                             ex:SheratonTenerife quot;Located direct...quot; 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     quot;What a lovely …quot; 0.7
                                                               ex:KnossosRoyal     quot;A surprisingly …quot; 0.2
                                                               ex:SheratonTenerife quot;Located direct...quot; 0.1

                                                        Join

                                                                                 µ                     t
              µ                  t
                                                                       ?h                 ?r
             ?h
                                                               ex:KnossosRoyal     quot;What a lovely …quot; 0.9
 ex:KnossosRoyal               0.7                             ex:KnossosRoyal     quot;A surprisingly …quot; 0.2
 ex:SheratonTenerife           0.1                             ex:SheratonTenerife quot;Located direct...quot; 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     quot;What a lovely …quot; 0.9
                                                               ex:SheratonTenerife quot;Located direct...quot; 0.8

                                                        EnTrust
                                                        0.5 , 1.0

                                                                                 µ                     t
                                                                       ?h                 ?r
                                                               ex:KnossosRoyal     quot;What a lovely …quot; 0.9
                                                               ex:KnossosRoyal     quot;A surprisingly …quot; 0.2
                                                               ex:SheratonTenerife quot;Located direct...quot; 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     quot;What a lovely …quot; 0.9
 ex:KnossosRoyal               0.7                        ex:KnossosRoyal     quot;A surprisingly …quot; 0.2
 ex:SheratonTenerife           0.1                        ex:SheratonTenerife quot;Located direct...quot; 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     quot;What a lovely …quot; 0.7
                                                               ex:SheratonTenerife quot;Located direct...quot; 0.8

                                                        Join

 {                                                   µ                      t
     { ?h rdf:type umbel:HotelBuilding ;
                                           ?h                 ?r
          p:location dbpedia:Heraklion . }
                                    ex:KnossosRoyal
     { ?h rev:hasReview [ rev:text ?txt1 ]             quot;What a lovely …quot; 0.9
       ENSURE TRUST ( 0.5 , 1.0 ) }ex:SheratonTenerife quot;Located direct...quot; 0.8
 }                                                                   EnTrust
                                                                     0.5 , 1.0

                                                                                 µ                    t
              µ                  t
                                                                     ?h                 ?r
             ?h
                                                          ex:KnossosRoyal     quot;What a lovely …quot; 0.9
 ex:KnossosRoyal               0.7                        ex:KnossosRoyal     quot;A surprisingly …quot; 0.2
 ex:SheratonTenerife           0.1                        ex:SheratonTenerife quot;Located direct...quot; 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     quot;What a lovely …quot; 0.7
                                                                  ex:SheratonTenerife quot;Located direct...quot; 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     quot;What a lovely …quot; 0.7
                                                                  ex:SheratonTenerife quot;Located direct...quot; 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     quot;What a lovely …quot; 0.9
 ex:KnossosRoyal               0.7                               ex:KnossosRoyal     quot;A surprisingly …quot; 0.2
 ex:SheratonTenerife           0.1                               ex:SheratonTenerife quot;Located direct...quot; 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             quot;What a lovely …quot; 0.7                ex:KnossosRoyal     quot;What a lovely …quot; 0.7
                                                                  ex:SheratonTenerife quot;Located direct...quot; 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     quot;What a lovely …quot; 0.7
       ENSURE TRUST ( 0.5 , 1.0 ) }ex:KnossosRoyal      quot;A surprisingly …quot; 0.2
     ENSURE TRUST ( 0.5 , 1.0 )     ex:SheratonTenerife quot;Located direct...quot; 0.1
 }
                                                          Join

                                                                                   µ                     t
              µ                  t
                                                                         ?h                 ?r
             ?h
                                                                 ex:KnossosRoyal     quot;What a lovely …quot; 0.9
 ex:KnossosRoyal               0.7                               ex:KnossosRoyal     quot;A surprisingly …quot; 0.2
 ex:SheratonTenerife           0.1                               ex:SheratonTenerife quot;Located direct...quot; 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             quot;What a lovely …quot; 0.7                ex:KnossosRoyal     quot;What a lovely …quot; 0.7
                                                                  ex:SheratonTenerife quot;Located direct...quot; 0.8
                                                        EnTrust
                                                        0.5 , 1.0

 ●   Position of the                                                               µ                     t
     ENSURE TRUST                                                        ?h                 ?r
     clause matters!                                             ex:KnossosRoyal     quot;What a lovely …quot; 0.7
                                                                 ex:KnossosRoyal     quot;A surprisingly …quot; 0.2
                                                                 ex:SheratonTenerife quot;Located direct...quot; 0.1

                                                          Join

                                                                                   µ                     t
              µ                  t
                                                                         ?h                 ?r
             ?h
                                                                 ex:KnossosRoyal     quot;What a lovely …quot; 0.7
 ex:KnossosRoyal               0.9                               ex:KnossosRoyal     quot;A surprisingly …quot; 0.2
 ex:SheratonTenerife           0.1                               ex:SheratonTenerife quot;Located direct...quot; 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     quot;What a lovely …quot; 0.9 0.9
                                                        ex:SheratonTenerife quot;Located direct...quot; 0.8 0.8

                                                 PrTrust
                                                    ?t

                                                                          µ                     t
                                                                ?h                     ?r
                                                        ex:KnossosRoyal     quot;What a lovely …quot; 0.9
                                                        ex:SheratonTenerife quot;Located direct...quot; 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

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Querying Trust in RDF Data with tSPARQL

  • 1. Querying Trust in RDF Data with tSPARQL Olaf Hartig http://olafhartig.de/foaf.rdf#olaf
  • 2. The Semantic Web is a reality ● Large amount of semantically interlinked data ● Applications emerge Olaf Hartig - Querying Trust in RDF Data with tSPARQL 2
  • 3. Is the data trustworthy? Olaf Hartig - Querying Trust in RDF Data with tSPARQL 3
  • 4. 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
  • 5. 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
  • 6. 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
  • 7. 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
  • 8. 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
  • 9. 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
  • 10. 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
  • 11. 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
  • 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 quot;What a lovely ...quot; http://revyu.../R337 quot;A surprisingly ...quot; Olaf Hartig - Querying Trust in RDF Data with tSPARQL 12
  • 13. 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 quot;What a lovely ...quot; http://revyu.../R337 quot;A surprisingly ...quot; Olaf Hartig - Querying Trust in RDF Data with tSPARQL 13
  • 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 quot;What a lovely ...quot; http://revyu.../R337 quot;A surprisingly ...quot; Olaf Hartig - Querying Trust in RDF Data with tSPARQL 14
  • 15. 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 quot;What a lovely ...quot; http://revyu.../R337 quot;A surprisingly ...quot; Olaf Hartig - Querying Trust in RDF Data with tSPARQL 15
  • 16. 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 quot;What a lovely ...quot; 0.7 http://revyu.../R337 quot;A surprisingly ...quot; Olaf Hartig - Querying Trust in RDF Data with tSPARQL 16
  • 17. 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 quot;What a lovely ...quot; 0.7 http://revyu.../R337 quot;A surprisingly ...quot; 0.2 Olaf Hartig - Querying Trust in RDF Data with tSPARQL 17
  • 18. 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
  • 19. 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
  • 20. Redefining the SPARQL algebra µ ?h ?r ex:KnossosRoyal quot;What a lovely …quot; ex:KnossosRoyal quot;A surprisingly …quot; ex:SheratonTenerife quot;Located direct...quot; Join µ µ ?h ?r ?h ex:KnossosRoyal quot;What a lovely …quot; ex:KnossosRoyal ex:KnossosRoyal quot;A surprisingly …quot; ex:SheratonTenerife ex:SheratonTenerife quot;Located direct...quot; 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
  • 21. Redefining the SPARQL algebra µ t ?h ?r ex:KnossosRoyal quot;What a lovely …quot; ex:KnossosRoyal quot;A surprisingly …quot; ex:SheratonTenerife quot;Located direct...quot; Join µ t µ t ?h ?r ?h ex:KnossosRoyal quot;What a lovely …quot; 0.9 ex:KnossosRoyal 0.7 ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ex:SheratonTenerife 0.1 ex:SheratonTenerife quot;Located direct...quot; 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
  • 22. 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 quot;What a lovely …quot; 0.7 ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ex:SheratonTenerife quot;Located direct...quot; 0.1 Join µ t µ t ?h ?r ?h ex:KnossosRoyal quot;What a lovely …quot; 0.9 ex:KnossosRoyal 0.7 ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ex:SheratonTenerife 0.1 ex:SheratonTenerife quot;Located direct...quot; 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
  • 23. 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
  • 24. 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
  • 25. 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
  • 26. 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
  • 27. 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
  • 28. Evaluating trust requirements ● Goal: ensuring a certain trustworthiness for the solutions of a specific graph pattern µ t ?h ?r ex:KnossosRoyal quot;What a lovely …quot; 0.9 ex:SheratonTenerife quot;Located direct...quot; 0.8 EnTrust 0.5 , 1.0 µ t ?h ?r ex:KnossosRoyal quot;What a lovely …quot; 0.9 ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ex:SheratonTenerife quot;Located direct...quot; 0.8 EnTrust l , u ,  = {  , t  ∣ , t ∈ ∧ lt u } * * Olaf Hartig - Querying Trust in RDF Data with tSPARQL 28
  • 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 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
  • 30. 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 quot;What a lovely …quot; 0.9 ex:KnossosRoyal 0.7 ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ex:SheratonTenerife 0.1 ex:SheratonTenerife quot;Located direct...quot; 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
  • 31. Evaluating trust requirementsµ t ?h ?r ex:KnossosRoyal quot;What a lovely …quot; 0.7 ex:SheratonTenerife quot;Located direct...quot; 0.8 Join { µ t { ?h rdf:type umbel:HotelBuilding ; ?h ?r p:location dbpedia:Heraklion . } ex:KnossosRoyal { ?h rev:hasReview [ rev:text ?txt1 ] quot;What a lovely …quot; 0.9 ENSURE TRUST ( 0.5 , 1.0 ) }ex:SheratonTenerife quot;Located direct...quot; 0.8 } EnTrust 0.5 , 1.0 µ t µ t ?h ?r ?h ex:KnossosRoyal quot;What a lovely …quot; 0.9 ex:KnossosRoyal 0.7 ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ex:SheratonTenerife 0.1 ex:SheratonTenerife quot;Located direct...quot; 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
  • 32. Evaluating trust requirementsµ t ?h ?r ex:KnossosRoyal quot;What a lovely …quot; 0.7 ex:SheratonTenerife quot;Located direct...quot; 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
  • 33. Evaluating trust requirementsµ t ?h ?r ex:KnossosRoyal quot;What a lovely …quot; 0.7 ex:SheratonTenerife quot;Located direct...quot; 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 quot;What a lovely …quot; 0.9 ex:KnossosRoyal 0.7 ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ex:SheratonTenerife 0.1 ex:SheratonTenerife quot;Located direct...quot; 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
  • 34. Evaluating trust requirementsµ µ t t ?h ?r ?h ?r ex:KnossosRoyal quot;What a lovely …quot; 0.7 ex:KnossosRoyal quot;What a lovely …quot; 0.7 ex:SheratonTenerife quot;Located direct...quot; 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 quot;What a lovely …quot; 0.7 ENSURE TRUST ( 0.5 , 1.0 ) }ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ENSURE TRUST ( 0.5 , 1.0 ) ex:SheratonTenerife quot;Located direct...quot; 0.1 } Join µ t µ t ?h ?r ?h ex:KnossosRoyal quot;What a lovely …quot; 0.9 ex:KnossosRoyal 0.7 ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ex:SheratonTenerife 0.1 ex:SheratonTenerife quot;Located direct...quot; 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
  • 35. Evaluating trust requirementsµ µ t t ?h ?r ?h ?r ex:KnossosRoyal quot;What a lovely …quot; 0.7 ex:KnossosRoyal quot;What a lovely …quot; 0.7 ex:SheratonTenerife quot;Located direct...quot; 0.8 EnTrust 0.5 , 1.0 ● Position of the µ t ENSURE TRUST ?h ?r clause matters! ex:KnossosRoyal quot;What a lovely …quot; 0.7 ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ex:SheratonTenerife quot;Located direct...quot; 0.1 Join µ t µ t ?h ?r ?h ex:KnossosRoyal quot;What a lovely …quot; 0.7 ex:KnossosRoyal 0.9 ex:KnossosRoyal quot;A surprisingly …quot; 0.2 ex:SheratonTenerife 0.1 ex:SheratonTenerife quot;Located direct...quot; 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
  • 36. 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
  • 37. 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 quot;What a lovely …quot; 0.9 0.9 ex:SheratonTenerife quot;Located direct...quot; 0.8 0.8 PrTrust ?t µ t ?h ?r ex:KnossosRoyal quot;What a lovely …quot; 0.9 ex:SheratonTenerife quot;Located direct...quot; 0.8 PrTrust v , * = {  ' , t  ∣  , t ∈* ∧  '=∪{  v , lt   } } Olaf Hartig - Querying Trust in RDF Data with tSPARQL 37
  • 38. 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
  • 39. 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
  • 40. 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
  • 41. 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
  • 42. 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