1.
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SW Software architecture
and SPARQL
Mariano Rodriguez-Muro,
Free University of Bozen-Bolzano

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Disclaimer

License


This work is licensed under a
Creative Commons Attribution-Share Alike 3.0 License
(http://creativecommons.org/licenses/by-sa/3.0/)
Material for these slides has been taken from

W3C pages for SPARQL

Jena and Sesame‟s documentation

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Summary

Semantic web idea, and overview of SWT

RDF data model

Jena intro

SPARQL protocol

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Reading material

Semantic Web Programming Part III, Chapter 8

FUSEKI tutorial

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SW Software architectures

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Architecture of SW applications

Local access


The RDF graph is stored
locally and is accessible
through an API
Mixed access

Manual (hard coded)

Federated Queries

Traversal

Remote access

The RDF graph is owned by
a third party and expossed
through an SPARQLendpoint or a web service

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Local Access
Triple stores and APIs

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Local access

Data is managed locally by
means of a triple store (e.g.,
Jena, Sesame)

Data may be:

RDF (e.g., local copies of
Linked Data

Legacy data transformed into
RDF (more in a few)

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Local access(triple stores)

Possible triple stores:
 Jena
TDB, SDB, Sesame, 4Store,
…
 Virtuoso, OWLIM, AllegroGra
ph,…

3rd party data:
 From DUMPs
 http://wiki.dbpedia.org/
 http://pro.europeana.eu/dat
asets
 Crawling (e.g, LDSpider)

Legacy transformation

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Local access (legacy sources)

3rd party tools to transform
 CSV
 XLS, etc.

XSLT to transform XML

Mapping based
(R2RML, D2RQ)
 3rd party tools to transform
RDBMS into RDF dumps
 3rd party tools to expose
RDBMS as virtual RDF

All of these will be covered in
the course

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Local access (local queries)

All triple stores offer SPARQL
execution

Accessible through console
tools (mysql and psql style)
bin/sparql --data=data-mydata.rdf
--query=my-sparql-query.rq

Through their own API

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SPARQL with Jena in Java

Key API objects

Query

QueryFactory

QueryExecutionFactory

QueryExecution

execAsk() > boolean

execConstruct() > Model

execDescribe() > Model

execSelect() > ResultSet
String queryString = "PREFIX owl:
<http://www.w3.org/2002/07/owl#> SELECT *
WHERE { ?x owl:sameas ?y }";
Query query =
QueryFactory.create(queryString);
QueryExecution qe =
QueryExecutionFactory.create(query, tdb);
ResultSet results = qe.execSelect();

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SPARQL with Jena in Java

ResultSet

Results from a query in a
table-like manner for
SELECT queries. Each row
corresponds to a set of
bindings which fulfil the
conditions of the query.
Access to the results is by
variable name.

getResultVars() >
List<String>

hasNext() > boolean

next() > QuerySolution
String queryString = "PREFIX owl:
<http://www.w3.org/2002/07/owl#> SELECT *
WHERE { ?x owl:sameas ?y }";
Query query =
QueryFactory.create(queryString);
QueryExecution qe =
QueryExecutionFactory.create(query, tdb);
ResultSet results = qe.execSelect();

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SPARQL with Jena in Java

QuerySolution

A single answer from a
SELECT query

varNames() >
Iterator<String>

contains(varname) > boolean

get(varname) > RDFNode

getResource(varname) >
Resource

getLiteral(varname) > Literal
String queryString = "PREFIX owl:
<http://www.w3.org/2002/07/owl#> SELECT *
WHERE { ?x owl:sameas ?y }";
Query query =
QueryFactory.create(queryString);
QueryExecution qe =
QueryExecutionFactory.create(query, tdb);
ResultSet results = qe.execSelect();

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SPARQL with Jena in Java

Tools for ResultSet

ResultSetFormatter


asRDF, asText,
asXMLString, asJSON…
Parameterized SPARQL
query
----------------------------------------------------| uri
|
=====================================================
| <http://www.opentox.org/api/1.1#NumericFeature> |
| <http://www.opentox.org/api/1.1#NominalFeature> |
| <http://www.opentox.org/api/1.1#StringFeature> |
| <http://www.opentox.org/api/1.1#Feature>
|
| <http://www.w3.org/2002/07/owl#Nothing>
|
| <http://www.opentox.org/api/1.1#Identifier>
|
| <http://www.opentox.org/api/1.1#ChemicalName> |
| <http://www.opentox.org/api/1.1#IUPACName>
|
| <http://www.opentox.org/api/1.1#InChI>
|
| <http://www.opentox.org/api/1.1#MolecularFormula> |
| <http://www.opentox.org/api/1.1#CASRN>
|
| <http://www.opentox.org/api/1.1#SMILES>
|
-----------------------------------------------------

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Remote Access
SPARQL Protocol

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Remote access (SPARQL Protocol)

Means to access query
processors

Compatible with RDF

Abstract specification

Bindings with the following
protocols:

HTTP

SOAP (WSDL)

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SPARQL Protocol

Main elements:
 operation
 one operation „query‟
 In message
 one sparql query
 zero or more datasets
 Out Message
 SPARQL results document
(for SELECT or ASK)
 An RDF graph serialized in
RDF/XML (for DESCRIBE
and CONSTRUCT)

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SPARQL Protocol

Means to access query
processors

Compatible with RDF

Abstract specification

Bindings with the following
protocols:

HTTP

SOAP (WSDL)

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SPARQL Protocol (HTTP bindings)

Uses HTTP GET and POST messages

Encoded query message (HTTP Encode)

Returns document in requested format (or the default)
PREFIX dc: <http://purl.org/dc/elements/1.1/>
SELECT ?book ?who
WHERE { ?book dc:creator ?who }

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SPARQL Protocol (HTTP bindings)

Request
GET /sparql/?query=EncodedQuery HTTP/1.1
Host: www.example
User-agent: my-sparql-client/0.1

Response (next page)

(Uses the XML formatting for SPARQL results)

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HTTP/1.1 200 OK
Date: Fri, 06 May 2005 20:55:12 GMT
Server: Apache/1.3.29 (Unix) PHP/4.3.4 DAV/1.0.3
Connection: close
Content-Type: application/sparql-results+xml
<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">
<head>
<variable name="book"/>
<variable name="who"/>
</head>
<results distinct="false" ordered="false">
<result>
<binding name="book"><uri>http://www.example/book/book5</uri></binding>
<binding name="who"><bnode>r29392923r2922</bnode></binding>
</result>
...
</sparql>

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SPARQL Protocol (HTTP bindings)

Request (specifying the default graph)
GET /sparql/?query=EncodedQuery&default-graph-uri=http://www.other.example/books HTTP/1.1
Host: www.other.example
User-agent: my-sparql-client/0.1

Response (next page)

Runs against the dataset identified by the URI:
http://www.other.example/books

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HTTP/1.1 200 OK
Date: Fri, 06 May 2005 20:55:12 GMT
Server: Apache/1.3.29 (Unix) PHP/4.3.4 DAV/1.0.3
Connection: close
Content-Type: application/sparql-results+xml
<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">
<head>
<variable name="book"/>
<variable name="who"/>
</head>
<results distinct="false" ordered="false">
<result>
<binding name="book"><uri>http://www.example/book/book5</uri></binding>
<binding name="who"><bnode>r29392923r2922</bnode></binding>
</result>
...
</sparql>

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SPARQL Protocol (HTTP bindings)

Request with content negotiation
GET /sparql/?query=EncodedQuery&default-graph-uri=http://www.example/jose-foaf.rdf HTTP/1.1
Host: www.example
User-agent: sparql-client/0.1
Accept: text/turtle, application/rdf+xml

Response (next page)

Using the format specified by the client

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HTTP/1.1 200 OK
Date: Fri, 06 May 2005 20:55:11 GMT
Server: Apache/1.3.29 (Unix)
Connection: close
Content-Type: text/turtle
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix foaf: <http://xmlns.com/foaf/0.1/>.
@prefix myfoaf: <http://www.example/jose/foaf.rdf#>.
myfoaf:jose foaf:name "Jose Jimeñez";
foaf:depiction <http://www.example/jose/jose.jpg>;
foaf:nick "Jo";
...

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SPARQL Protocol (SOAP bindings)

A protocol for accessing web services

Based on HTTP and XML

Messages are passed through envelopes

SPARQL requests and responses are embedded in the
envelopes

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SPARQL Protocol (SOAP bindings)

Request (note content type, encoding of the query)
POST /services/sparql-query HTTP/1.1
Content-Type: application/soap+xml
Accept: application/soap+xml, multipart/related, text/*
User-Agent: Axis/1.2.1
Host: www.example
SOAPAction: ""
Content-Length: 438
<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchemainstance">
<soapenv:Body>
<query-request xmlns="http://www.w3.org/2005/09/sparql-protocol-types/#">
<query>SELECT ?z {?x ?y ?z . FILTER regex(?z, 'Harry')}</query>
</query-request>
</soapenv:Body>
</soapenv:Envelope>

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SPARQL Protocol (SOAP bindings)

Response is a SOAP message embedding SPARQL/XML
HTTP/1.1 200 OK
Content-Type: application/soap+xml
<?xml version="1.0" encoding="utf-8"?>
<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soapenv:Body>
<query-result xmlns="http://www.w3.org/2005/09/sparql-protocol-types/#">
<ns1:sparql xmlns:ns1="http://www.w3.org/2005/sparql-results#">
<ns1:head>
<ns1:variable name="z"/>
</ns1:head>
<ns1:results distinct="false" ordered="false">
<ns1:result>
<ns1:binding name="z">
<ns1:literal>Harry Potter and the Chamber of Secrets</ns1:literal>
</ns1:binding>
</ns1:result>
...
</ns1:results>
</ns1:sparql>
</query-result>
</soapenv:Body>
</soapenv:Envelope>

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SPARQL Protocol (SOAP bindings)

Response is a SOAP message embedding SPARQL/XML
HTTP/1.1 200 OK
Content-Type: application/soap+xml
<?xml version="1.0" encoding="utf-8"?>
<soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soapenv:Body>
<query-result xmlns="http://www.w3.org/2005/09/sparql-protocol-types/#">
<ns1:sparql xmlns:ns1="http://www.w3.org/2005/sparql-results#">
<ns1:head>
<ns1:variable name="z"/>
</ns1:head>
<ns1:results distinct="false" ordered="false">
<ns1:result>
<ns1:binding name="z">
<ns1:literal>Harry Potter and the Chamber of Secrets</ns1:literal>
</ns1:binding>
</ns1:result>
...
</ns1:results>
</ns1:sparql>
</query-result>
</soapenv:Body>
</soapenv:Envelope>

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Remote access (SPARQLendpoints)

A SPARQL processor that is accessible
through the SPARQL protocol

Many open endpoints:
http://www.w3.org/wiki/SparqlEndpoints

Often accessible through query forms, e.g.:

Dbpedia:
http://dbpedia.org/sparql

BBC programme information:
http://lod.openlinksw.com/sparql/

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Remote access (SPARQLendpoints)

Using implementing the SPARQL protocol
on your own, or

Using a library that supports the SPARQL
protocol:

Python: RDFLib

PHP: librdf, RAP

JavaScript

Java: Jena, Sesame, etc

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Remote access (SPARQLendpoints with Jena)

In Jena:
String location = “http://dbpedia.org/sparql”;
String query = “PREFIX …. SELECT …. “;
QueryExecution x = QueryExecutionFactory.sparqlService(location, query);
ResultSet results = x.execSelect();
ResultSetFormatter.out(System.out, results);

The library hides all details about the protocol. You can use the
normal API calls and objects to work with the results.

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Remote Access
Creating SPARQL endpoints

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Creating a SPARQL end-point

Most triple stores include a HTTP implementation of the
SPARQL protocol

Set up depends on the system

Jena‟s way is by mean of JOSEKI now (FUSEKI)

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Setting up Joseki

Package comes with



Server JARs
Scripts to manage the server and data
Once the system is running, the control panel can be found at:
http://localhost:3030/

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Running a Fuseki Server

fuseki-server --mem /DatasetPathName
create an empty, in-memory dataset

fuseki-server --file=FILE /DatasetPathName
create an empty, in-memory dataset and load FILE into it

fuseki-server --loc=DB /DatasetPathName
Use an existing TDB database, or create one if it doesn‟t exist.

fuseki-server --config=ConfigFile
construct one ore more endpoints based on the config. desc.

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Server URI scheme

http://*host*/dataset/query
the SPARQL query endpoint.

http://*host*/dataset/update
the SPARQL Update language endpoint.

http://*host*/dataset/data
the SPARQL Graph Store Protocol endpoint.

http://*host*/dataset/upload
the file upload endpoint.
Default port 3030

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Script Control

Load data
s-put http://localhost:3030/ds/data default books.ttl

Get it back
s-get http://localhost:3030/ds/data default

Query it with SPARQL using the .../query endpoint.
s-query --service http://localhost:3030/ds/query 'SELECT * {?s ?p ?o}'

Update it with SPARQL using the .../update endpoint.
s-update --service http://localhost:3030/ds/update 'CLEAR DEFAULT'

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Summary

Covered:


SPARQL endpoints

Creating and managing
endpoints


SPARQL through APIS
HTTP Protocol
Later

Transforming data into RDF

Virtual RDF (R2RML, D2RQ)

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See also

http://www.w3.org/TR/rdf-sparql-protocol/

http://jena.apache.org/documentation/serving_data/

Not discussed here: Serving LOD with dereferencable URI‟s
and the SPARQL protocol

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Sesame