Rules for the Semantic Web

Rules for the Semantic Web Dipartimento di Informatica, Sistemistica e Comunicazione Università di Milano-Bicocca [email protected] ale....
Author: Augustus Bates
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Rules for the Semantic Web Dipartimento di Informatica, Sistemistica e Comunicazione Università di Milano-Bicocca

[email protected]





[email protected] [email protected] [email protected]

tel. 02 6448 7835 tel. 02 6448 7879

Semantic Web I have a dream for the Web [in which computers] become capable of analyzing all the data on the Web – the content, links, and transactions between people and computers. A ‘Semantic Web’, which should make this possible, has yet to emerge, but when it does, the day-to-day mechanisms of trade, bureaucracy and our daily lives will be handled by machines talking to machines. The ‘intelligent agents’ people have touted for ages will finally materialize. Tim Berners-Lee, 1999

Semantic Web Layer Cake User Interface & Applications

today:

SWRL (Semantic Web Rule Language)

tomorrow: Rule Interchange Format Working Group RIF (Rule Interchange Format)

Unifying logic

OWL Reasoning Cart #1

hasPrice

contains

320€

contains contains

Item #1

Item #2

hasPrice 100€

Item #3 hasPrice

hasPrice 150€

70€

• “The total price is the sum of the price of the items in the cart” • OWL lacks of support for this kind of reasoning !

SWRL (Semantic Web Rule Language) SWRL is a a rules-language, combining OWL (Lite or DL) with RuleML (Rule Markup Language)

OWL (Lite/DL)

RuleML

SWRL

Example (human readable) hasPrice(?x1,?p1)

hasPrice(?x2,?p2)

lessThan (?p1,?p2)

isCheaper(?x1,?x2)

http://www.w3.org/Submission/SWRL/

Timeline DLV is a Disjunctive Datalog System

CLIPS is a software tool for building expert systems. The name is an acronym for "C Language Integrated Production System." The first versions of CLIPS were developed starting in 1985 at NASA-Johnson Space Center

DLV

SWRL

1997

2004

Prolog is a general purpose logic programming language

CLIPS Prolog

1985

Semantic Web Rule Language

1995

2001 RuleML

Jess

1972 1980

Datalog is a subset of Prolog. It is a query and rule language for deductive databases

Datalog

Jess, a rule engine for the Java platform

The Rule Markup Initiative has taken steps towards defining a shared Rule Markup Language, permitting both forward and backward rules in XML

Decidability Decidability: Terminates after a finite amount of time and correctly decides

OWL (Lite/DL)

RuleML

SWRL Decidability ?

No

SWRL Alternative: DLP

OWL

DLP

Logic Programing (Datalog)

Decidability ?

YES

Datalog rules

facts Example Datalog program:

facts

parent(bill,mary). parent(mary,john).

rules

ancestor(X,Y) :- parent(X,Y). ancestor(X,Y) :- ancestor(X,Z),ancestor(Z,Y).?-

Datalog Engine

Query: ?- ancestor(bill,X).

ancestor(bill,mary). ancestor(bill,john).

query

result

RuleML (Rule Markup Language) • RuleML is a family of languages developed to express both forward and backward rules in XML for deduction, rewriting, and further inferential-transformational tasks • Example: XSLT (Extensible Stylesheet Language Transformations) is a restricted termrewriting system of rules, written in XML, for transforming XML documents into other documents http://www.ruleml.org/

SWRL Rule Example hasPrice(?x1,?p1)

hasPrice(?x2,?p2)

lessThan (?p1,?p2)

isCheaper(?x1,?x2)

In the abstract syntax the rule would be written like: Implies ( Antecedent( hasPrice(I-variable(x1) I-variable(p1)) swrlb: hasPrice(I-variable(x2) I-variable(p2)) namespace for the swrlb:lessThan(I-variable(p1) I-variable(p2))) SWRL Built-ins

Consequent( isCheaper(I-variable(x1) I-variable(x2))))

Rule Example in RDF Concrete Syntax

swrl: namespace for the SWRL

ruleml: namespace for the SWRL Built-ins

RDF Triples...

Architecture from datalog...

...to SWRL rules

facts

SWRL rules

Reasoner + SWRL Engine

Datalog Engine

query

owl (T-Box, A-Box)

result

query

result

SWRL Editor The SWRLTab is a development environment for working with SWRL rules in Protégé. It supports the editing and execution of SWRL rules.

The Protégé distribution does not include any rule engines. At present, only the Jess is supported.

Reasoner Pellet is an open source OWL Reasoner and SWRL Engine

http://pellet.owldl.com/

Search RDF Data An RDF graph can contains a huge number of statements, but how can you find and manipulate the data you need within RDF graphs?

SPARQL is a query Language for RDF SPARQL is a product of the w3c RDF Data Access Working group (DAWG). 4 core specs:

Current status: proposed recomendation Last revision: 12 november 2007

- SPARQL Query Language for RDF - SPARQL Protocol for RDF - SPARQL Query Results XML Format - RDF Data Access Use Cases and Requirements

http://www.w3.org/2001/sw/DataAccess/

http://www.w3.org/TR/rdf-sparql-query/

What is a Query ? A Query is question. Answering requires understanding: An RDF graph

Data graph

Query graph

SPARQL uses • The query RDF graph for queries • The thing queried • The relationship between them

SPARQL Query Engine

Results (table, boolean)

SPARQL Query Types Ground graphs as queries

Boolean query Returns TRUE if Data Graph => Query Graph ASK WHERE { book:0001 book:author author:01 . }

ASK Other SPARQL query types:

DESCRIBE, CONSTRUCT

Variable

SELECT SELECT ?author WHERE { book:0001 book:author ?author . }

Blank nodes as query variables

There is an answer if data graph query graph

Results is a Table, not a Graph

A simple query Find the URL of the blog by the person named “Jon Foobar”

Data graph

query type (SELECT)

Basic graph structure for a single contributor in bloggers.rdf source: Philip McCarthy

result variable

PREFIX foaf: SELECT ?url WHERE { ?contributor foaf:name "Jon Foobar" . ?contributor foaf:weblog ?url . }

subject

predicate

object (variable)

Query graph in RDF Turtle notation

Results

SPARQL Query

Data graph

One more example @prefix dc: . _:author1 "J.K. Rowling" .

dc:title "Harry Potter and the Chamber of Secrets" . dc:creator _:author1 . dc:title "Harry Potter and the Prisoner Of Azkaban" . dc:creator _:author1 .

PREFIX books: PREFIX dc: PREFIX vcard: SELECT ?bookTitle ?authorName WHERE { ?book dc:creator ?author . ?book dc:title ?bookTitle . ?author vcard:FN ?authorName }

bookTitle

authorName

Harry Potter and the Chamber of Secrets

J.K. Rowling

Harry Potter and the Prisoner Of Azkaban

J.K. Rowling

Try this example online: http://www.sparql.org/query.html

Value constraints ASK WHERE { ?author vcard:FN “J.K. Rowling” . }

This query returns true iff there is an author with name “J.K. Rowling”

SPARQL provides an operation to test strings, based on regular expressions. The syntax is different from the SQL “LIKE” ! ASK WHERE { ?author vcard:FN ?name . FILTER regex(?name, "rowling", "i") }

Filter Pattern ASK WHERE { person:0001 info:age ?age . FILTER (?age >= 18) }

This query returns true iff an author names contains the string “rowling” Filter flags: “i” means “Case insensitive”

The regular expression language is the XQuery regular expression language which is codified version of that found in Perl.

Filter on an integer property. This query returns true iff there is a person 0001 has age >= 18

http://www.w3.org/TR/xpath-functions/#regex-syntax

http://www.perl.org

Value constraints Filter on the value of an integer property. SELECT ?name ?age WHERE { ?person info:name ?name . ?person info:age ?age . FILTER (?age >= 18) }

This query returns the name and age of each person with age >= 18

SPARQL has a the ability to query for data but not to fail query when that data does not exist. SELECT ?name ?age WHERE { ?person info:name ?name . OPTIONAL { ?person info:age ?age . FILTER ( ?age > 18 ) } }

This query returns the name and age of each person with unknown age or age >= 18

Architecture (revised) Ontology Storage

Ontology Update

owl (T-Box, A-Box)

SWRL rules

Reasoner + SWRL Engine

SPARQL queries

User Interface

SPARQL Engine results

Useful links w3c RDF Data Access Working group: http://www.w3.org/2001/sw/DataAccess/ SPARQL Woking Draft: http://www.w3.org/TR/rdf-sparql-query/ Jena SPARQL tutorial: http://jena.sourceforge.net/ARQ/Tutorial/index.html SPARQL Regular expression: http://www.w3.org/TR/xpath-functions/#regex-syntax Online SPARQL query: http://www.sparql.org/query.html