SPARQL Query Language for RDF

SPARQLQUERY LANGUAGE FOR RDF

Agenda

• Introduction

• Graph Patterns

• Query Execution and Ordering

• Query Forms

• Testing Values

• SPARQL Support

The XML approach is to "wrap" each data item in start/end tags

<Aircraft> <wingspan>14.8 meters</wingspan> <weight>512 kilograms</weight> <cruise-speed>70 knots</cruise-speed> <range>400 nautical miles</range> <description> medium-altitude, long-endurance unmanned aerial vehicle </description></Aircraft>

RQ-1.xml

Why use OWL?

Why use OWL?

• The purpose of this document is to describe the role that OWL plays in data interoperability. [Note: this is not the only use of OWL, but it is an important one.]

• Contents:– Understanding Syntax versus Semantics– An example that shows why standardizing syntax is

necessary but not sufficient– Migrating from defining semantics on a per-

application basis to standardized semantics

Syntax versus Semantics

• Syntax: the structure of your data– e.g., XML mandates that you structure your data by "wrapping"

each data item within a start tag and an end tag pair, with the end tag being preceded by / and both tags in <…> brackets.

– That is, XML specifies the syntax of your data. • Semantics: the meaning of your data

• Two conditions necessary for interoperability:

1. Adopt a common syntax: this enables applications to parse the data. XML provides a common syntax, and thus is a critical first step. 2. Adopt a means for understanding the semantics: this enables applications to use the data. OWL provides a standard way of expressing the semantics.

What is this XML snippet talking about, i.e., what are the semantics?

<Predator> …</Predator>

What is a Predator?

Predator - which one?

• Predator: a medium-altitude, long-endurance unmanned aerial vehicle system.

• Predator : one that victimizes, plunders, or destroys, especially for one's own gain.

• Predator : an organism that lives by preying on other organisms.• Predator: a company which specializes in camouflage attire.• Predator: a video game.• Predator: software for machine networking.• Predator: a chain of paintball stores.

Meaning (semantics) applied on a per-application basis

<Predator> …</Predator>

application

Semantics: A Predator is type ofAircraft.Actions: These actions must be performed on the Predator data: - identify ground control station. - determine onboard sensors. - determine ordnance.

Meaning (semantics) applied on a per-application basis

XML

app#1Semantics: Code to interpret the dataAction: Code to process the data

app#2Semantics: Code to interpret the dataAction: Code to process the data

Problem with attaching semantics on a per-application basis

applicationSemantics: Code to interpret the dataAction: Code to process the data

Problems with burying semantic definitionswithin each application:- Duplicate effort - Each application must express the semantics- Variability of interpretation - Each application can take its own interpretation - Example: Mars probe disaster - one application interpreted the data in inches, another application interpreted the data in centimeters.- No ad-hoc discovery and exploitation - Applications have the semantics pre-wired. Thus, when new data (e.g., new type of aircraft) is encountered an application may not be able to effectively process it. This makes for brittle applications.

What's a better approach?

Better approach:(1) Extricate semantic definitions from applications (2) Express semantic definitions in a standard vocabulary XML

app#1Action: Code to process the data

app#2Action: Code to process the data

OWL DocumentSemantic Definitions

OWL provides an agreed-upon vocabulary for expressing semantics

A Sampling of the OWL Vocabulary:

subClassOf: this OWL element is used to assert that one class of items is a subset of another class of items. Example: Predator is a subClassOf Aircraft.

FunctionalProperty: this OWL element is used to assert that a property has a unique value. Example: sensorID is a FunctionalProperty, i.e., sensorID has a unique value.

equivalentClass: this OWL element is used to assert that one Class is equivalent to another Class. Example: Platform is an equivalentClass to Aircraft.

OWL Enables Machines to Understand Data!

XML/DTD/XML Schemas

OWL

Syntax

Semantics

OWL enables machine-processable semantics!

Ontology (definition)

• An Ontology is the collection of semantic definitions for a domain.

• Example: an Aircraft Ontology is the set of semantic definitions for the Aircraft domain, e.g.,– Predator is a subClassOf Aircraft.– sensorID is a FunctionalProperty.

– Platform is an equivalentClass to Aircraft.

Why use OWL?

• Benefits to application developers:– Less code to write (save $$$).

– Less chance of misinterpretation (save $$$).

• Benefits to community at large:– Everyone can understand each other's data's semantics,

since they are in a common language.

– OWL uses the XML syntax to express semantics, i.e., it builds on an existing technology.

• Don't have to learn new syntax.

• Common XML tools (e.g., parsers) can work on OWL.

– OWL will soon be a W3C recommendation.

XQuery Databases

• XQuery is an XML query language. • It can be used to efficiently and easily extract information

from Native XML Databases (NXD).• It can be used to query XML views of relational data.

Database Systems supporting XQuery

• The following database systems offer XQuery support: – Native XML Databases:

• Berkeley DB XML• eXist• MarkLogic• Software AG Tamino• Raining Data TigerLogic• Documentum xDb (X-Hive/DB)

– Relational Databases: • IBM DB2• Microsoft SQL Server• Oracle

Native XML Database (NXD)

• Native XML databases have an XML-based internal model, i.e., their fundamental unit of storage is XML.

Copyright 2004 Digital Enterprise Research Institute. All rights reserved.

www.deri.org

OWL Tutorial

Introduction

• RDF – flexible and extensible way to represent information about WWW resources

• SPARQL - query language for getting information from RDF graphs. It provides facilities to:– extract information in the form of URIs, blank nodes, plain and typed

literals.

– extract RDF subgraphs.

– construct new RDF graphs based on information in the queried graphs

• matching graph patterns • variables – global scope; indicated by ‘?‘ or ‘$‘ • query terms – based on Turtle syntax• terms delimited by "<>" are relative URI references • data description format - Turtle

Graph Patterns

Basic Graph Pattern – set of Triple Patterns

Group Pattern - a set of graph patterns must all match

Value Constraints - restrict RDF terms in a solution

Optional Graph Patterns .- additional patterns may extend the solution

Alternative Graph Pattern – two or more possible patterns are tried

Patterns on Named Graphs - patterns are matched against named graphs

Basic Graph Pattern

• Set of Triple Patterns– Triple Pattern – similar to an RDF Triple (subject, predicate,

object), but any component can be a query variable; literal subjects are allowed

– Matching a triple pattern to a graph: bindings between variables and RDF Terms

• Matching of Basic Graph Patterns– A Pattern Solution of Graph Pattern GP on graph G is any

substitution S such that S(GP) is a subgraph of G.

x v

rdf:type rdf:Property

rdf:type rdf:type rdf:PropertySELECT ?x ?v WHERE { ?x ?x ?v }

?book dc:title ?title

Basic Graph Pattern - Multiple Matches

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name ?mbox

WHERE

{ ?x foaf:name ?name .

?x foaf:mbox ?mbox }

@prefix foaf: <http://xmlns.com/foaf/0.1/> .

_:a foaf:name "Johnny Lee Outlaw" .

_:a foaf:mbox <mailto:[email protected]> .

_:b foaf:name "Peter Goodguy" .

_:b foaf:mbox <mailto:[email protected]> .

name mbox

"Johnny Lee Outlaw"

<mailto:[email protected]>

"Peter Goodguy" <mailto:[email protected]>

Group Graph Pattern (set of graph patterns) also!

Data

Query

Query Result

Basic Graph Pattern - Blank Nodes

PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?x ?name

WHERE { ?x foaf:name ?name }


_:a foaf:name "Alice" .

_:b foaf:name "Bob" .

x name

_:c “Alice“

_:d “Bob”

Data

Query

Query Result

Graph Patterns







Group Pattern


SELECT ?name ?mbox

WHERE

{ ?x foaf:name ?name .

?x foaf:mbox ?mbox }


SELECT ?name ?mbox

WHERE

{ {?x foaf:name ?name;

foaf:mbox ?mbox }

}

Graph Patterns







Value Constraints

PREFIX dc: <http://purl.org/dc/elements/1.1/>

PREFIX ns: <http://example.org/ns#>

SELECT ?title ?price

WHERE { ?x ns:price ?price .

FILTER ?price < 30 .

?x dc:title ?title . }

@prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix : <http://example.org/book/> .

@prefix ns: <http://example.org/ns#> .

:book1 dc:title "SPARQL Tutorial" .

:book1 ns:price 42 .

:book2 dc:title "The Semantic Web" .


title price

"The Semantic Web" 23

Data

Query

Query Result

Graph Patterns







Optional graph patterns


PREFIX ns: <http://example.org/ns#>

SELECT ?title ?price

WHERE { ?x dc:title ?title .

OPTIONAL { ?x ns:price ?price .

FILTER ?price < 30 }}

@prefix dc: <http://purl.org/dc/elements/1.1/> .

@prefix : <http://example.org/book/> .

@prefix ns: <http://example.org/ns#> .

:book1 dc:title "SPARQL Tutorial" .


:book2 dc:title "The Semantic Web" .


title price

“SPARQL Tutorial“

"The Semantic Web" 23

Data

Query

Query Result

Multiple Optional Blocks


SELECT ?name ?mbox ?hpage

WHERE { ?x foaf:name ?name .

OPTIONAL { ?x foaf:mbox ?mbox }. OPTIONAL { ?x foaf:homepage ?hpage } }


@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .


_:a foaf:homepage <http://work.example.org/alice/> .



Data

Query

Query Result

name Mbox hpage

“Alice“ <http://work.example.org/alice/>

“Bob“ <mailto:[email protected]>

Graph Patterns

Basic Graph Patterns – set of Triple Patterns

Group Patterns - a set of graph patterns must all match



Alternative Graph Patterns – two or more possible patterns are tried


Alternative Graph Patterns

PREFIX dc10: <http://purl.org/dc/elements/1.0/>

PREFIX dc11: <http://purl.org/dc/elements/1.1/>

SELECT ?x ?y

WHERE { { ?book dc10:title ?x } UNION { ?book dc11:title ?y } }

@prefix dc10: <http://purl.org/dc/elements/1.0/> .

@prefix dc11: <http://purl.org/dc/elements/1.1/> .

_:a dc10:title "SPARQL Query Language Tutorial" .

_:b dc11:title "SPARQL Protocol Tutorial" .

_:c dc10:title "SPARQL" .

_:c dc11:title "SPARQL (updated)" .

Data

Query

Query Result

x y

"SPARQL (updated)"

"SPARQL Protocol Tutorial"

"SPARQL"

"SPARQL Query Language Tutorial"

Graph Patterns







RDF Dataset

• RDF data stores may hold multiple RDF graphs:– record information about each graph– queries that involve information from more than one graph – RDF Dataset in SPARQL terminology– the background graph, which does not have a name, and zero or

more named graphs, identified by URI reference

• the relationship between named and background graphs:– (i) to have information in the background graph that includes

provenance information about the named graphs (the application is not directly trusting the information in the named graphs )

– (ii) to include the information in the named graphs in the background graph as well.

RDF Dataset- The Relationship between Named and Background Graphs (I)

# Background graph

@prefix dc: <http://purl.org/dc/elements/1.1/> .

<http://example.org/bob> dc:publisher "Bob" .

<http://example.org/alice> dc:publisher "Alice" .

# Graph: http://example.org/bob


_:a foaf:name "Bob" .


# Graph: http://example.org/alice




RDF Dataset- The Relationship between Named and Background Graphs (II)

# Background graph

@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:x foaf:name "Bob" .

_:x foaf:mbox <mailto:[email protected]> .

_:y foaf:name "Alice" .

_:y foaf:mbox <mailto:[email protected]> .

# Graph: http://example.org/bob


_:a foaf:name "Bob" .


# Graph: http://example.org/alice




Querying the Dataset

# Graph: http://example.org/foaf/aliceFoaf


@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .



_:a foaf:knows _:b .

_:b rdfs:seeAlso <http://example.org/foaf/bobFoaf> .

<http://example.org/foaf/bobFoaf> rdf:type foaf:PersonalProfileDocument .



_:b foaf:age 32 . # Graph: http://example.org/foaf/bobFoaf


@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .

_:1 foaf:mbox <mailto:[email protected]> .

_:1 rdfs:seeAlso <http://example.org/foaf/bobFoaf> .

_:1 foaf:age 35 .

<http://example.org/foaf/bobFoaf> rdf:type foaf:PersonalProfileDocument .

Querying the Dataset - Accessing Graph Labels


SELECT ?src ?bobAge

WHERE { GRAPH ?src

{ ?x foaf:mbox <mailto:[email protected]> .

?x foaf:age ?bobAge }

}

src bobAge

<http://example.org/foaf/aliceFoaf> 32

<http://example.org/foaf/bobFoaf> 35

Querying the Dataset - Restricting by Graph Label


PREFIX data: <http://example.org/foaf/>

SELECT ?age

WHERE

{

GRAPH data:bobFoaf {

?x foaf:mbox <mailto:[email protected]> .

?x foaf:age ?age }

}

age

35

Querying the Dataset - Restricting via Query Pattern

PREFIX data: <http://example.org/foaf/>


PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>

SELECT ?mbox ?age ?ppd

WHERE

{ GRAPH data:aliceFoaf

{ ?alice foaf:mbox <mailto:[email protected]> ;

foaf:knows ?whom .

?whom foaf:mbox ?mbox ;

rdfs:seeAlso ?ppd .

?ppd a foaf:PersonalProfileDocument . } .

GRAPH ?ppd { ?w foaf:mbox ?mbox ;

foaf:age ?age } }

mbox age ppd

<mailto:[email protected]> 35 <http://example.org/foaf/bobFoaf>

Query Execution and Ordering

• Optional-1: an optional pattern that has a common variable with a(more) basic graph pattern(s) must be executed after the basic graph pattern(s)

• Optional-2: there can't be two optionals with a common variable, if that variable does not occur in a basic graph pattern as well

• Constraint: constraints are evaluated after variables are assigned values

Query forms:

– SELECT

• returns all, or a subset of the variables bound in a query pattern match

• formats : XML or RDF/XML

– CONSTRUCT • returns an RDF graph constructed by substituting variables in a

set of triple templates

– DESCRIBE• returns an RDF graph that describes the resources found.

– ASK• returns whether a query pattern matches or not.

CONSTRUCT Examples(I)




@prefix vcard: <http://www.w3.org/2001/vcard-rdf/3.0#>.

<http://example.org/person#Alice> vcard:FN "Alice" .

PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX vcard: <http://www.w3.org/2001/vcard-rdf/3.0#> CONSTRUCT { <http://example.org/person#Alice> vcard:FN ?name } WHERE { ?x foaf:name ?name }

#extracting a whole graph from the target RDF dataset

CONSTRUCT { ?s ?p ?o }

WHERE { GRAPH <http://example.org/myGraph> { ?s ?p ?o } . }

CONSTRUCT Examples(II)


PREFIX app: <http://example.org/ns#>

CONSTRUCT { ?s ?p ?o }

WHERE { GRAPH ?g { ?s ?p ?o } .

{ ?g dc:publisher <http://www.w3.org/> } .

{ ?g dc:date ?date } .

FILTER app:myDate(?date) > "2005-02-8T00:00:00Z"^^xsd:dateTime. }

accesing a graph conditional on other information contained in the metadata about named graphs in the dataset

DESCRIBE

PREFIX ent: <http://myorg.example/employees#> DESCRIBE ?x

WHERE { ?x ent:employeeId "1234" }


@prefix vcard: <http://www.w3.org/2001/vcard-rdf/3.0> .

@prefix myOrg: <http://myorg.example/employees#> .

_:a myOrg:employeeId "1234" ;

foaf:mbox_sha1sum "ABCD1234" ;

vcard:N [ vcard:Family "Smith" ;

vcard:Given "John" ] .

foaf:mbox_sha1sum rdf:type owl:InverseFunctionalProperty .

ASK


@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .


_:a foaf:homepage <http://work.example.org/alice/> .




ASK { ?x foaf:name "Alice" } .

Testing Values

• Named functions and syntactically constructed operations: – operands: subset of XML Schema DataTypes {xsd:string,

xsd:decimal, xsd:double, xsd:dateTime} and types derived from xsd:decimal.

• Subset of XPath functions and operators– Operands: xs:string, xs:double, xs:float, xs:decimal, xs:integer, xs:dateTime – additional operators: sop:RDFterm-equal, sop:bound , sop:isURI,

sop:isBlank, sop:isLiteral, sop:str , sop:lang, sop:datatype, sop:logical-or, sop:logical-and

• Type Promotion : xs:double, xs:float, xs:decimal– each of the numeric types is promoted to any type higher in the

above list when used as an argument to function expecting that higher type.

Support for SPARQL

• SPARQL and Jena– module called ARQ that implements SPARQL; also parses

queries expressed in RDQL or its own internal language.– not yet part of the standard Jena distribution; availbale from

either Jena‘s CVS repository or as a self-contained download

• Twinkle – simple Java interface that wraps the ARQ SPARQL Processor

library (the add-on to Jena).

• Redland– set of free software packages that provide support for RDF,

including querying with RDQL and SPARQL using the Rasqal RDF Query Library. .

SPARQL Query Language for RDF

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