Semantic Web 101

David Ratcliffe & Armin HallerCSIRO ICT Centre, Canberra23rd April 2012

Semantic Web 101Canberra Semantic Web meetup

INFORMATION ENGINEERING LABORATORY

What is the Semantic Web?

“The Semantic Web is a web of data, in some ways like a global database”1

“The first step is putting data on the Web in a form that machines can naturally understand, or converting it to that form. This creates what I call a Semantic Web - a Web of data that can be processed directly or indirectly by machines”2

1. http://www.w3.org/DesignIssues/Semantic.html

2. Tim Berners-Lee, Weaving the Web. Harper, San Francisco, 1999.

CSIRO. Semantic Web 101 – Canberra Semantic Web meetup

FundamentalzZzZz…

Linked Open Data RDFa, -Formats Vocabularies GRDDL Triplestores Apps!

RDFS, OWLRDF, SPARQLURIs, XML

Fundamentals: Semantic Web “Layer Cake”

Linked Open Data RDFa, -Formats Vocabularies RDDL Triplestores Apps!

URIs, RDF, RDFS,SPARQL, OWL

Fundamentals

Linked Open Data RDFa, -Formats Vocabularies GRDDL Triplestores Web Applications!

URIs, RDF, RDFS,SPARQL, OWL

String of characters identifying a resource (which can be… anything!)Syntax (absolute):

<scheme> : <path> [? <query>] [# <fragment>]Examples:

ICT Centre website:http://www.ict.csiro.au/

The actual ICT Centre itself:http://www.ict.csiro.au/resource#id

URIs are more general than URLs (and less so than IRIs!) URIs include URNs (e.g., urn:oid:2.16.840)

Used extensively in the Linked Open Data web! Many recommendations about URIs to come…

Uniform Resource Identifiers (URIs)

Resource Description Framework (RDF)

Data model - captures knowledge about resources (as URIs!)

Relates resources with predicates (named relationships)Australian War Memorial located_in Canberra

The ‘triple’ data modelSubject, predicate, object

Data model - captures knowledge about resources

All knowledge can be encoded using triples like this in RDF

Canberra is located_in ACT(…‘subjects’ can be ‘objects’ – links resources!)

XML Serialization

Australian War Memorial located_in Canberra

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:obo="http://purl.obolibrary.org/obo/OBO_REL#" xmlns:dbpprop="http://dbpedia.org/property/"> <rdf:Description rdf:about="http://dbpedia.org/resource/Australian_War_Memorial"> <obo:_located_in> <rdf:Description rdf:about="http://dbpedia.org/resource/Canberra"/> </obo:_located_in> <rdf:Description></rdf:RDF>

XML Serialization

“” unveiled 1941

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:obo="http://purl.obolibrary.org/obo/OBO_REL#" xmlns:dbpprop="http://dbpedia.org/property/"> <rdf:Description rdf:about="http://dbpedia.org/resource/Australian_War_Memorial"> <obo:_located_in> <rdf:Description rdf:about="http://dbpedia.org/resource/Canberra"/> </obo:_located_in> <dbpprop:unveiled rdf:datatype="http://www.w3.org/2001/XMLSchema#int"> 1941 </dbpprop:unveiled> <rdf:Description></rdf:RDF>

XML Serialization

“” unveiled 1941 (integer data type)

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:obo="http://purl.obolibrary.org/obo/OBO_REL#" xmlns:dbpprop="http://dbpedia.org/property/"> <rdf:Description rdf:about="http://dbpedia.org/resource/Australian_War_Memorial"> <obo:_located_in> <rdf:Description rdf:about="http://dbpedia.org/resource/Canberra"/> </obo:_located_in> <dbpprop:unveiled rdf:datatype="http://www.w3.org/2001/XMLSchema#int"> 1941 </dbpprop:unveiled> <rdf:Description></rdf:RDF>

RDF Graph

Collection of triples referencing common resource(s) = a graph

Canberra located_in ACT

Australian War Memorial unveiled 1941

Australian_War_Memorial

Canberra

{1941}

_located_in

RDF ‘Triplestore’ – Database for triples

Basically a database for triples, stored as graphs

Triplestores not only store triples, but give you ways of getting them out in interesting ways… (e.g., via queries – SPARQL)

Canberra

{1941}

_located_in

Data modelRelational data (tables)

Data instancesRecords in tables

Query supportSQL

Indexing mechanismOptimized for evaluating queries as relational expressions

Relational Database RDF Triplestore

Data modelRDF graphs

Data instancesRDF triples

Query supportSPARQL

Indexing mechanismOptimized for evaluating queries as graph patterns

Language for querying (and constructing new) RDF graphs A W3C Recommendation (version 1.1 released in January 2012) Syntax similar to SQL…

SPARQL Protocol and RDF Query Language (SPARQL)

PREFIX dbpedia:<http://dbpedia.org/resource/>PREFIX obo:<http://purl.obolibrary.org/obo/OBO_REL#>SELECT ?lWHERE {

dbpedia:Australian_War_Memorial obo:_located_in ?l .}

SPARQL – Anatomy (simple SELECT)

PREFIXDefine prefix for URI to make SPARQL more readable

SELECT Variables (columns) in the result (here, ?l)

WHEREThe graph pattern to look for involving the selected variables…“Where [?l] is the Australian_War_Memorial _located_in?”

SPARQL: Querying an RDF graph

e.g. “Where is the Australian_War_Memorial _located_in?”

Canberra

{1941}

_located_in

Canberra

{1941}

_located_in

Result:

http://dbpedia.org/resource/Canberra

Canberra

{1941}

_located_in

RDF Schema (RDFS)

Describes structures of triples into particular graphs Assigns semantics to RDF triples

(…just as E-R does for relational data!) Used in describing vocabularies and ontologies over RDF

RDFS: Structure + Semantics over RDF

Class (set) of instances (set members): E.g., class ‘City’ – the set of all cities

Canberra

Subclass (subset) of a class (set) of instances (set members): Class ‘CapitalCity’ (subclass of ‘City’) –

defined as the set of all cities that are the capital of a federated state

Canberra

CapitalCity

StateCapital

CapitalCity

Subclass (subset) of a class (set) of instances (set members): Class ‘StateCapital’ (subclass of ‘City’) –

defined as the set of all cities that are capitals of a state within a federated state

Cities that are CapitalCity and StateCapital

Canberra

Properties (set set) of instances (set members) over classes:

observes: Sensor Observation

_located_in

Federated State

StateCapital

CapitalCity

Canberra ACT

More (+ expressive) structure and semantics…

Web Ontology Language (OWL)

FederalStateCapital = CapitalCity StateCapital

_located_in

Federated State

StateCapital

CapitalCity

That’s enough…

... for putting Data openly on the Web …

and linking it to other data …

a.k.a. Linked Open Data Building a web of data Semantic Web done right Combination of Openess with data + open standards uses RDF with de-referenceable URIs → not only to identify data

but actually pointing to data about the entity

What is this all useful for?

Linked

Linking data paves the way for all kinds of improvements in: search, filtering, automation…

Real Business Value “I found that RDFa was a much more stable concept – based on the use of long established

vocabularies (also known as ontologies) that have existed for years. …Within just a couple of months, we began to see an increase in our organic search results … by 30% over historical rates. We also saw an increase in our click-through rate.” [Jay Myers, Lead Development Engineer Best Buy]

“2012: The Year of the Semantic Web” [Steve Hamby, CTO, Orbis Technologies, Inc.]

Enormous amount of linked (RDF) data already available• Many vocabularies to get your data described and linked into this world• Estimated tens (to hundreds) of billions of triple statements• Now (relatively) easier for people to join in!

Motivation

LOD ‘Cloud’ Growth: September 2010

[Richard Cyganiak, Anja Jentzsch, Linking Open Data cloud diagram, 2010]

LOD ‘Cloud’ Growth: September 2011

[Richard Cyganiak, Anja Jentzsch, Linking Open Data cloud diagram, 2011]

Tim Berners-Lee outlined 4 principles for Publishing Linked Open Data:

1. Use URIs for names of things

2. Use HTTP URIs so that people can look up those names

3. When someone looks up a HTTP URI, provide useful information (using the standards, like RDF)

4. Include links to other URIs so that a user can discover more things.

The Four Linked Open Data Principles

Source: http://www.w3.org/DesignIssues/LinkedData.html

Use URIs for names of things – Example:

Large US retailer

Loads of different products for sale!

Data include:Product categories(computers, videogames, televisions,digital cameras, mp3players, mobile phones,appliances, etc…)

Product data: Price Model # ID Stock levels Rating Reviews Images etc…

Identify things to reference with a URI

Store data: Names Locations Phone # Hours Ratings/Reviews Events etc…

Source: http://www.readwriteweb.com/archives/how_best_buy_is_using_the_semantic_web.php

Identify things to reference with a URI

Which URI to usefor the location

Carbondale, Illinois, USA?

Choose URIs for things in your data

http://www.ci.carbondale.il.us/

http://en.wikipedia.org/wiki/Carbondale,_Illinois

Problem:http://www.ci.carbondale.il.us/ http://en.wikipedia.org/wiki/Carbondale,_Illinois

These are webpages about Carbondale, IL!

Instead, we want some identifier for the town Carbondale, IL.

DBpedia has an RDF Resource URI based on info from Wikipedia:

http://dbpedia.org/resource/Carbondale,_Illinois

DBpedia is a major Linked Open Data contributor!

So, what happens when we put: http://dbpedia.org/resource/Carbondale,_Illinois

… into a browser?

The dbpedia.org server responds with an HTTP redirect:303 SEE OTHERLOCATION: http://dbpedia.org/page/Carbondale,_Illinois

Use de-referenceable HTTP URIs

The browser (client) performs content negotiation with the server:ACCEPT parameters in the HTTP request specified HTML, e.g.:

Accept: text/*, text/html, text/html;level=1, */*

The client could have asked for RDF instead!

Accept: application/rdf+xml

… or other syntaxes too (N3, Turtle, etc.):

Accept: application/rdf+xml, text/rdf+n3, …

Content negotiation

http://dbpedia.org/page/Carbondale,_Illinois

Content negotiation

So, what happens when we ask for: http://dbpedia.org/resource/Carbondale,_Illinois including:

Accept: application/rdf+xml

The dbpedia.org server responds with another, different redirect:303 SEE OTHERLOCATION: http://dbpedia.org/data/Carbondale,_Illinois

The server may provide the triple data in RDF/XML format...

Content negotiation

http://dbpedia.org/data/Carbondale,_Illinois

Content negotiation

Three Different URIs for different data about the same thing:1. An abstract identifier (RDF resource) for the ‘thing’ in question2. An HTML page about that ‘thing’3. Some RDF data about that ‘thing’

Example: Carbondale, IL on dbpedia.org:

1. Abstract identifier: http://dbpedia.org/resource/Carbondale,_Illinois

2. HTML page: http://dbpedia.org/page/Carbondale,_Illinois

3. RDF data: http://dbpedia.org/data/Carbondale,_Illinois

Different URIs for different content!

Broken links are very uncool

URIs that don’t change are cool. Should strive to maintain URIs! Even if content moves,

server should still responds appropriately.

Make sure your URIs are cool

RDF data usually resides in an RDF database (Triplestore)

…how do we ‘put them out’ on the web?

SPARQL Endpoint (SPARQL query over HTTP)• Direct connection to triplestore over HTTP

Publish RDF data in files on your web server• Might not even need a triplestore…

Providing RDF on the Web

Problem: Web data (HTML) and RDF data are separate.

Separate HTML content and RDF data?

WebPage

(HTML)RDFdata

Exposing RDF on the web

Separate HTML content and RDF data?

Maintenance problem• Both need to be managed separately• RDF content and web content have much overlap (redundancy)

duplication of content, effort = data integrity issues• RDF/XML difficult to author = extra overhead

Verification problem• How to reconcile differences as content changes?

Visibility problem• Easy to ignore the RDF stuff!

(out of sight, out of mind)

Embed RDF into your web content using RDFa

WebPage

(HTML)RDFdata

‘Embed’ RDF into HTML instead!

Embed RDF into your web content using RDFa

Extra (RDFa) markup is ignored by web browsers.

RDF – in attributes (RDFa)

Source: Peter Mika (Yahoo!), RDFa, 2011

…but is “one of the… what I call a gateway drug… to the Semantic Web.” Jay Myers, Lead Development Engineer for Best Buy

RDFa is not the only solution…

4. Include links to other URIs so that a users can discover more things.

For describing classes (categories) and properties (relationships), try to re-use existing vocabularies

Easier to interoperate if we’re talking the same language!

Many vocabularies/ontologies out there: schema.org is a great place to start looking! Vocabs for products (Good Relations), people (FOAF), social media (SIOC), places,

events, businesses, e-commerce, music, etc., you name it…

If nothing relevant, you can: Hack existing vocabularies, then publish your dirty hacks on http://open.vocab.org/ Create your own, but make sure you…

Publish it!Reconcile (map) it to other vocabularies, if you can.

Link to existing vocabularies to describe data!

Linking similar entities (individuals/ concepts) from different datasets (“entity resolution”)

Several ways, different semantics: owl:equivalentClass – strong assertion! owl:sameAs – strong assertion! rdfs:seeAlso – weak (loose) relation skos:closeMatch – weak (loose) relation skos:exactMatch – stronger than close match skos:related – weak semantic relation

http://dbpedia.org/resource/Canberra owl:sameAs

http://rdf.freebase.com/rdf/en.canberra

Link your data!

Thank you!ICT CentreDavid RatcliffePhD Student / Software Engineer

Phone: +61 2 6216 7001David.Ratcliffe@csiro.au

ICT CentreDr. Armin HallerOffice Manager, Australian W3C Office

Phone: +61 2 6216 7149Armin@w3.org

ICT CENTRE, INFORMATION ENGINEERING LABORATORY

Semantic Web 101

Technology

Transcript of Semantic Web 101

Semantic Web Technologies Organization€¦ · – Semantic Web standards and languages – Programming for the semantic web – Creating semantic web data • Exercise – Understand

Semantic Search with Semantic Web

Ontology 101 - New York Semantic Technology Conference

The Semantic Web meets Resource Management · Terena EuroCAMP, 2006-04-03 RDF 101 The Semantic Web meets Resource Management 1

Towards a semantic web Philip Hider. This talk The Semantic Web vision Scenarios Standards Semantic Web & RDA.

Semantic Web WS 2016/17 - STI Innsbruck · Semantic Web Services Semantic Web Technology + Web Service Technology => Semantic Web Services as integrated solution for realizing the

Semantic Web & Semantic Web Processes

Semantic Web In Industry R. Guha. Two Levels of the Semantic Web Deep Semantic Web: –Intelligent agents performing inference –Semantic Web as distributed.

Corporate Semantic Web · Web-basiertes Semantisches Unternehmen (Semantic Enterprise) Corporate Semantic Web •Semantic Applications •Semantic Knowledge •Semantic Content Front

Semantic Web Technologies Resource Description Framework …€¦ · :semantic-web dc:subject "Semantic Web"@en . • Triples sharing the same subject or subject+predicate::semantic-web

Web Semantic

Searching The Semantic Webnisansa/Classes/02... · Semantic Web Research Laboratory Sharif University of Technology 6Searching The Semantic Web Introduction Semantic web has some

Semantic Technology for Development: Semantic Web without the Web?

20.10.2009, 01-Vom WWW zum Semantic Web, Vorlesung Semantic Web

Semantic Web & Ontology. Introduction Semantic Web and Ontology.

Python programming | Semantic Web · 2014-10-14 · Python programming | Semantic Web What is Semantic Web? Semantic Web = Triple data structure (representing subject, verb and object)

Transforming the existing web into a semantic webaboulsaadat.com/wael/teaching/309/ex/practical... · Transforming the existing web into a semantic web w eb plumbing 101 by Eran Shir

Semantic web 101: Benefits for geologists

Semantic Blogging : Spreading the Semantic Web Meme fileblogging This paper is about semantic blogging, an application of the semantic web to blogging. The semantic web promises to

October 19, 20051 Semantic Web. October 19, 20052 Semantic Web Part 3: Semantic Web.