ekaw - triple pattern fragments

Triple Pattern Fragments Ruben Taelman - @rubensworks

imec - Ghent University

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Evaluate SPARQL queries client-side with TPF

SELECT ?person ?city WHERE { ?person rdf:type dbpedia-owl:Artist. ?person dbpedia-owl:birthPlace ?city. ?city foaf:name "Waterloo"@en.}

?person rdf:type dbpedia-owl:Artist.

?person dbpedia-owl:birthPlace ?city.

?city foaf:name "Waterloo"@en. 2

Publishing with Triple Pattern FragmentsServer

Client

Evaluations

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Client

Evaluations

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Simple triple pattern interfaceTriple pattern queries, paged results

Example: s1 p1 o1 at page 2

http://example.org/my-dataset?subject=s1&predicate=p1&object=o1&page=2

Metadata and controls

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Effective caching because of limited number of URI’sFrequently used TPF’s are cached

Cached TPF’s can be delivered efficiently

Queries with common data fragments will evaluate faster

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Storage solution must support triple pattern queriesIn-memory triplestore for RDF files

HDT (Fernández 2010)

SPARQL endpoints

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Server is simpleIn order to make publication cheap and easy

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Client

Evaluations

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Clients can evaluate any SPARQL queryusing the simple TPF interface of one or more servers

Split up SPARQL queries into separate triple pattern queries

Combine results client-side

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Joining triple pattern fragments can be tricky

SELECT ?person ?city WHERE { ?person rdf:type dbpedia-owl:Artist. ?person dbpedia-owl:birthPlace ?city. ?city foaf:name "Waterloo"@en.}



?city foaf:name "Waterloo"@en.

Some query plans are more efficient than others

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Number of triples as metadata in TPF’s




96 000

12 000 000

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Select most selective triple pattern




96 000

12 000 000

Most selective!

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Find all results for most selective pattern




dbp:Waterloo,_Iowa foaf:name "Waterloo"@endbp:Waterloo,_London foaf:name "Waterloo"@endbp:Waterloo,_Ontario foaf:name "Waterloo"@en...

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Fill in results in other patterns


?person dbpedia-owl:birthPlace dbp:Waterloo,_Iowa.


dbp:Waterloo,_Iowa foaf:name "Waterloo"@endbp:Waterloo,_London foaf:name "Waterloo"@endbp:Waterloo,_Ontario foaf:name "Waterloo"@en...

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Recursively repeat for remaining patterns


?person dbpedia-owl:birthPlace dbp:Waterloo,_Iowa .

96 000

45

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Select most selective pattern



96 000

45

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Find all results for most selective pattern



96 000

45

dbp:Allan_Carpenter dbo:birthPlace dbp:Waterloo,_Iowa.dbp:Adam_DeVine dbo:birthPlace dbp:Waterloo,_Iowa.dbp:Bonnie_Koloc dbo:birthPlace dbp:Waterloo,_Iowa....

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Fill in results in other patterns

dbp:Allan_Carpenter rdf:type dbpedia-owl:Artist.


96 000

45

dbp:Allan_Carpenter dbo:birthPlace dbp:Waterloo,_Iowa.dbp:Adam_DeVine dbo:birthPlace dbp:Waterloo,_Iowa.dbp:Bonnie_Koloc dbo:birthPlace dbp:Waterloo,_Iowa....

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One solution is found

dbp:Allan_Carpenter rdf:type dbpedia-owl:Artist. 1

Repeat process for all other matches

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Joining algorithm is not always optimalOther algorithms are possible

Improved algorithm minimizes #requests (Van Herwegen 2015)

Additional metadata may improve query plans

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Client

Evaluations

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Send many client queries to a single server1 server (TPF, Virtuoso, Fuseki)

1 - 244 simultaneous clients

Different query types from Berlin SPARQL benchmark

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(Verborgh 2016)

Query throughput is lower

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Server load is lower

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TPF is just one possible trade-offReduce client load:

Additional metadata for membership search (Vander Sande 2015)

Substring filtering (Van Herwegen 2015)

Dynamic data publication and querying (Taelman 2016)

Reduce server load:

Decentralized caching (Folz 2016)

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ConclusionsTPF servers have a simple low-cost interface

TPF clients evaluate SPARQL queries locally, using this interface

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Next sessionSetting up a TPF server yourself

Querying the server

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SourcesR Verborgh “Linked Data Publishing” http://rubenverborgh.github.io/WebFundamentals/linked-data-publishing/

R. Verborgh, M. Vander Sande, O. Hartig, et al. Triple Pattern Fragments: a Low-cost Knowledge Graph Interface for the Web.

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http://rubenverborgh.github.io/WebFundamentals/linked-data-publishing/

http://rubenverborgh.github.io/WebFundamentals/linked-data-publishing/

ekaw - triple pattern fragments

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