How good is your SPARQL endpoint? A QoS-Aware SPARQL Endpoint Monitoring and Data Source Selection Mechanism for Federated SPARQL Queries

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How good isyour SPARQL endpoint? A QoS-aware SPARQL endpoint monitoring and data source selection mechanism for federated SPARQL queries Ali Intizar and Alessandra Mileo

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Linked Open Dataand SPARQL Endpoints • Linked Data • LOD cloud 2 28/10/2014

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Linked Open Dataand SPARQL Endpoints • Linked Data • LOD cloud 2 28/10/2014

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Linked Open Dataand SPARQL Endpoints • Linked Data • LOD cloud • SPARQL Endpoints 2 28/10/2014

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Linked Open Dataand SPARQL Endpoints • Linked Data • LOD cloud • SPARQL Endpoints • Both pubic and private 2 28/10/2014

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Linked Open Dataand SPARQL Endpoints • Linked Data • LOD cloud • SPARQL Endpoints • Both pubic and private • Allow easy access to linked data using SPARQL queries • Provide a querying interface 2 28/10/2014

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Linked Open Dataand SPARQL Endpoints • Linked Data • LOD cloud • SPARQL Endpoints • Both pubic and private • Allow easy access to linked data using SPARQL queries • Provide a querying interface • Open Data Management Tools 2 28/10/2014

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Linked Open Dataand SPARQL Endpoints • Linked Data • LOD cloud • SPARQL Endpoints • Both pubic and private • Allow easy access to linked data using SPARQL queries • Provide a querying interface • Open Data Management Tools • Datahub 2 28/10/2014

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Linked Open Dataand SPARQL Endpoints • Linked Data • LOD cloud • SPARQL Endpoints • Both pubic and private • Allow easy access to linked data using SPARQL queries • Provide a querying interface • Open Data Management Tools • Datahub • LOD Stats 28/10/2014 2

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Linked Open Dataand SPARQL Endpoints • Linked Data • LOD cloud • SPARQL Endpoints • Both pubic and private • Allow easy access to linked data using SPARQL queries • Provide a querying interface • Open Data Management Tools • Datahub • LOD Stats • SPARQL Endpoint Description • Vocabulary for Interlinking Datasets • Service Description 28/10/2014 2

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Ranking of theSPARQL Endpoints • Multiple SPARQL endpoints can represent the same dataset 3 28/10/2014

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Ranking of theSPARQL Endpoints • Multiple SPARQL endpoints can represent the same dataset • Which one is the best for me? 3 28/10/2014

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Ranking of theSPARQL Endpoints • Multiple SPARQL endpoints can represent the same dataset • Ranking of the SPARQL endpoints 3 28/10/2014

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Ranking of theSPARQL Endpoints • Multiple SPARQL endpoints can represent the same dataset • Ranking of the SPARQL endpoints • Based on QoI/QoS Parameters 4 28/10/2014

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Ranking of theSPARQL Endpoints • Multiple SPARQL endpoints can represent the same dataset • Ranking of the SPARQL endpoints • Based on QoI/QoS Parameters 4 28/10/2014

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QoS Parameters forSPARQL Endpoints For QoS based ranking of the SPARQL endpoints • Identification of the various QoS parameters associated with the SPARQL endpoints • Semantic respresentation of the identified QoS parameters • Extension of the existing SPARQL endpoints description vocabularies (VoID/SD) to associate QoS parameters • Evaluation techniques for the QoS metrics • Continuous monitoring of the SPARQL endpoints to generate QoS profiles 5 28/10/2014

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QoS Parameters forSPARQL Endpoints 28/10/2014 • Performance • Response Time • Execution Time • Throughput • Error Rate 6

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QoS Parameters forSPARQL Endpoints • Performance • Response Time • Execution Time • Throughput • Error Rate • Data Quality • Accuracy • Data Consistency • Completeness • Freshness 6 28/10/2014

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QoS Parameters forSPARQL Endpoints • Interoperabiilty • SPARQL Version • Additional Features • Restricted Features 7 28/10/2014

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QoS Parameters forSPARQL Endpoints • Interoperabiilty • SPARQL Version • Additional Features • Restricted Features • Availability • UpTime • DownTime • MeanUpTime • MTTR 7 28/10/2014

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QoS Parameters forSPARQL Endpoints • Licensing • PDDL • ODC-By • ODC-ODbL • CC0 0.1 Universal 8 28/10/2014

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QoS Parameters forSPARQL Endpoints • Licensing • PDDL • ODC-By • ODC-ODbL • CC0 0.1 Universal • ResultSet • Size Limit • Result Format 8 28/10/2014

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QoS Parameters forSPARQL Endpoints • Licensing • PDDL • ODC-By • ODC-ODbL • CC0 0.1 Universal • ResultSet • Size Limit • Result Format • Dataset Description • VoID • SD 8 28/10/2014

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QoS Parameters forSPARQL Endpoints • Semantic Description of SPARQL Endpoint (VoID/SD) • QoS Profile of SPARQL Endpoints SPARQL Endpoint has QoSProfileEndpoint QoSProfile QoSProfileDefault QoSProfileUser Property SubClass 10 28/10/2014

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QoS Parameters forSPARQL Endpoints • Semantic Description of SPARQL Endpoint • QoS Profile of SPARQL Endpoints SPARQL Endpoint has QoSProfileEndpoint QoSProfile QoSProfileDefault QoSProfileUser Property SubClass 10 28/10/2014

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QoS Parameters forSPARQL Endpoints • Semantic Description of SPARQL Endpoint • QoS Profile of SPARQL Endpoints SPARQL Endpoint has QoSProfileEndpoint QoSProfile QoSProfileDefault QoSProfileUser Property SubClass 10 28/10/2014

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QoS Parameters forSPARQL Endpoints • Semantic Description of SPARQL Endpoint • QoS Profile of SPARQL Endpoints • QoS Profile 1. Endpoint SPARQL Endpoint 2. Default 3. User has QoSProfileEndpoint QoSProfile QoSProfileDefault QoSProfileUser Property SubClass 10 28/10/2014

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QoS Parameters forSPARQL Endpoints hasValue QoSProfile QoSParame ter Name QoSWeight sameAs 11 28/10/2014 QoSCategory Value QoSMetric Tendency NonNumericMe tric ExactNumeric NumericMetric IntervalNumeric QoSUnit BooleanMetric LinguisticMe tric GradingMetric No Low Mid High Numeric Value TextValue Yes hasvalue hasvalue hasvalue hasvalue hasvalue start end hasName hasTendency hasCategory contains hasWeight hasMetric isMeasuredIn

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Evaluation of theQoS Parameters • Performance • Response Time Q1 . SELECT ?p where { <s> ?p <o> } Q2 . SELECT ?o where { s1 p1 ?o s2 p2 ?o } 13 28/10/2014

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Evaluation of theQoS Parameters • Performance • Response Time • Execution Time Q1 . SELECT ?p where { <s> ?p <o> } Q2 . SELECT ?o where { s1 p1 ?o s2 p2 ?o } Q3 . SELECT * where { ? s ?p ?o } LIMIT 1000 14 28/10/2014

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Evaluation of theQoS Parameters • Performance • Response Time • Execution Time • Throughput Repeated execution of Q1. 15 28/10/2014

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Evaluation of theQoS Parameters • Performance • Response Time • Execution Time • Throughput • Error Rate By putting the counter on the error returns by the SPARQL endpoint during the execution of the queries 16 28/10/2014

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Evaluation of theQoS Parameters • Interoperabiilty • SPARQL Version • Additional Features • Restricted Features • SPARQL 1.1 test data set 17 28/10/2014

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Evaluation of theQoS Parameters • Availability • UpTime • DownTime • MeanUpTime • MTTR • We rely on the service provider for the provision of initial UpTime. • Periodic execution of query Q1 to monitor availability • Started the counter of DownTime whenever Q1 failed • MeanUpTime calculated as percentage of the time SPARQL endpoint was available since its initial UpTime. • Mean Time To Recover (MTTR) is calculated as average time taken by SPARQL endpoint to recover after failure. 18 28/10/2014

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Evaluation of theQoS Parameters • Licensing • PDDL • ODC-By • ODC-ODbL • CC0 0.1 Universal Q6 . PREFIX dcterms : <http://purl.org/dc/terms/> SELECT ?license WHERE { ?ds a void:Dataset . ?ds dcterms:license ?license . } 19 28/10/2014

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Evaluation of theQoS Parameters • Dataset Description • Vocabulary for Interlinking Datasets • Service Description Q4 . PREFIX void : <http://rdfs.org/ns/void#> SELECT ?ds WHERE { ?ds a void:Dataset . ?ds void:SPARQLEndpoint <SPRQLEnpointURI> } 20 28/10/2014

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Evaluation of theQoS Parameters • ResultSet • Size Limit • Result Format Q5 . PREFIX sd: <http://www.w3.org/ns/sparql-service-description#> SELECT ?format WHERE { ?s a sd:service . ?s sd:endpoint <endpointURI> . ?s sd:resultFormat ?format . } 21 28/10/2014

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Evaluation of theQoS Parameters • Data Quality • Accuracy • Data Consistency • Completeness • Freshness Data quality is an overlap between quality of information(QoI) and quality of service(QoS) 22 28/10/2014

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Monitoring QoS metricsof SPARQL endpoints • Montioring • Runtime • Periodic 24 28/10/2014

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Monitoring QoS metricsof SPARQL endpoints • Montioring • Runtime • Periodic • QoS Profile Generation 24 28/10/2014

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Federated SPARQL Queries • SPARQL 1.1 extension provides SERVICE keyword • Allows remotely execution of the SPARQL queries on several endpoints Federated SPARQL Query Engine Source Selection Indexing/Caching Optimiser Query Execution SPARQL SPARQL SPARQL Endpoint Endpoint Endpoint … SPARQL Endpoint SPARQL 25 28/10/2014

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Federated SPARQL Queries • Problem of data source selection • Automated discovery and execution of the SPARQL endpoints for any federated query. Federated SPARQL Query Engine Source Selection Indexing/Caching Optimiser Query Execution SPARQL SPARQL SPARQL Endpoint Endpoint Endpoint … SPARQL Endpoint SPARQL 26 28/10/2014

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Federated SPARQL Queries • Problem of data source selection • Automated discovery and execution of the SPARQL endpoints for any federated query. • Candidate Data Sources: “Given a user's query Q and set of n data sources DS = { dsi | i =1..n} , we define set of candidate data sources as DSc = { dscj | j = 1..m } that can potentially contribute to answer query Q, where DSc ⊆ DS and 1 ≤ m ≤ n . “ 27 28/10/2014

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Federated SPARQL Queries • Problem of data source selection • Automated discovery and execution of the SPARQL endpoints for any federated query. • QoS Aware Data Sources: “Given a set of candidate data sources DSc, we define set of QoS aware data sources as DSqos = { dsqosk | k = 1..l } as set of optimal data sources that can potentially contribute to the answer of the Query Q and are compliant with the QoS requirements mentioned in the query, where DSqos ⊆ DSc and 1 ≤ l ≤ m ≤ n . “ 28 28/10/2014

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QoS-Aware Federated SPARQLQueries Federated SPARQL Query Engine QoS Aware Query Parser Source Selection Indexing/Caching QoS Aware Source Selection QoS Repository QoS Evaluation 29 28/10/2014 Optimiser Query Execution SPARQL SPARQL SPARQL Endpoint Endpoint Endpoint … SPARQL Endpoint User Query & QoS SPARQL DSc DSqos QoSProfile Monitoring

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SPARQL Extension withQoS • QoS requirements can be described as part of the SPARQL query • We introduce a new QOSREQ keyword in the SPARQL query language • QOSREQ operator is applied to the triple pattern or BGP immediarly proceeding the operator • Comma separated values of multiple QoS parameters within QOSREQ operator • Comparison operators to compare the user defined QoS requirements with QoS profile of the SPARQL endpoint 30 28/10/2014

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SPARQL Extension withQoS • QoS requirements can be described as part of the SPARQL query SELECT ?drug ?keggUrl ?chebiImage WHERE { ?drug rdf:type drugbank:drugs . QOSREQ[ qs:ResponseTime < 10 , qs:SizeLimit > 10000] ?drug drugbank:keggCompoundId ?keggDrug . ?keggDrug bio2rdf:u r l ?keggUrl . { ?drug drugbank:genericName ?drugBankName . ?chebiDrug purl:title ?drugBankName . } QOSREQ[ qs:DatasetDescription = 'VoID' , qs:MeanUpTime > 80 ] ?chebiDrug chebi:image ?chebiImage . } 30 28/10/2014

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Experimental Evaluation •FedBench Benchmark • A benchmark suite for federated SPARQL queries evaluation • Provides various data sets from Life Sciences, Linked Data and Cross Domains • 25 queries to evaluate the performance • Testbed • Datasets are deployed as SPARQL endpoints • Multiple Copies of the data sets to create higher number of candidate data sources • Human intervention to create fluctuation • Montioring of the SPARQL endpoints for more than 2 months • QoS Profiles generation and updates in QoS metrics values based on continuous monitoring 32 28/10/2014

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33 28/10/2014 ExperimentalEvaluation 0" 5" 10" 15" 20" CD1" CD2" CD3" CD4" CD5" CD6" CD7" LS1" LS2" LS3" LS4" LS5" LS6" LS7" LD1" LD2" LD3" LD4" LD5" LD6" LD7" LD8" LD9" LD10" LD11" No."of"Selected"Data"Sources" FedX?QBenchmark" Splendind?QBenchmark" QoSAware?QDefault" QoSAware?Quser"

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34 28/10/2014 ExperimentalEvaluation 0" 5" 10" 15" CD1" CD2" CD3" CD4" CD5" CD6" CD7" LS1" LS2" LS3" LS4" LS5" LS6" LS7" LD1" LD2" LD3" LD4" LD5" LD6" LD7" LD8" LD9" LD10" LD11" No."of"Selected"Data"Sources" Q_50" Q_75" Q_100"

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Conclusion • Identificationand semantic representation of the QoS parameters of the SPARQL endpoints • QoS metrics evaluation mechanism • A monitoring Service for QoS Evaluation • SPARQL extension for users QoS requirements within query language • QoS-Aware Federated SPARQL query evaluation 35 28/10/2014

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Future Work •QoS monitoring over public SPARQL endpoints & integration with SPARQLES • Sophisticated mechanisms for Quality of Information evaluation • Taking QoS requirements as well preferences into account (Hard and Soft Constraints) • QoS aggregated values 35 28/10/2014

How good is your SPARQL endpoint? A QoS-Aware SPARQL Endpoint Monitoring and Data Source Selection Mechanism for Federated SPARQL Queries

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How good is your SPARQL endpoint? A QoS-Aware SPARQL Endpoint Monitoring and Data Source Selection Mechanism for Federated SPARQL Queries