Digital Enterprise Research Institute Semantic Web Technologies: From

Digital Enterprise Research Institute Semantic Web Technologies: From

Digital Enterprise Research Institute Semantic Web Technologies: From Theory to Standards Axel Polleres Digital Enterprise Research Institute, NUI Galway Copyright 2009 Digital Enterprise Research Institute. All rights reserved. www.deri.i e A bit of History Digital Enterprise Research Institute Tim Berners-Lee 1980: Enquire within upon everything Bidirectional links typed links , single machines ENQUIRE used already terms like

"Universal Document Identifier" Hypertext Tim Bernes lee March 1989 "Information Management: A Proposal" written by Tim BL and circulated for comments at CERN (TBL). 2 www.deri.i e A bit of History lets look closer Digital Enterprise Research Institute HTML has only information about layout but the original idea had much more 3 www.deri.i e

The Semantic Web in W3Cs view: Digital Enterprise Research Institute 3. Shall allow us to ask structured queries on the Web www.deri.i e 2. Shall allow us to describe the structure of information in machine readable form: RDFS+OWL+RIF 1. Shall allow us to publish structured information on the Web: XML+RDF 4 Focus in this talk: Digital Enterprise Research Institute www.deri.i e

Which theory do these Sem. Web standards base on? Whats missing? (= Do these standards work together) (Brief overview of own contributions/solutions in this area, details in the references, paper is meant as a literature survey, entry point) 5 Digital Enterprise Research Institute 6 www.deri.i e 1. Structured Data on the Web Digital Enterprise Research Institute Prof. Scott Kelso gives a Keynote at AICS name(person1, Kelso ). )

isA :name "Scott21st Kelso" . http://aics.nuigalway.ie/ns/aics2010 The National Conference on Artificial RDF+RDF Schema can be Intelligence and Cognitive Science :Conference :hasKeynote embedded in FOL [deBruijn or Datalog [deBruijn et http://aics.nuigalway.ie/ns/talk1 . :hasKeynote Scott

Kelso al. 2007] [Ianni et al. 2009] hasKeynote(aics2010, talk1) talk1). :presentedBy :presentedBy :name ... http://aics.nuigalway.ie/ns/person1 Scott . Kelso presentedBy(talk1,person1) presentedBy(talk1,person1). 7 www.deri.i e RDF is the basis for Linked Data: Digital Enterprise Research Institute

www.deri.i e Everything gets a URI (conferences, people, talks, ) These URIs are linked via RDF describing relations Relations are URIs again (e.g. :name) When I dereference the URIs, I should find more information about them 1. 2. 3. 4. 8 RDF Data on the Web: Linked Open Data Digital Enterprise Research Institute March 2008 July 2009 March 2009 9

www.deri.i e RDF Data online: Example 1/3 Digital Enterprise Research Institute (i) directly by the publishers (ii) by exporters www.deri.i e FOAF/RDF linked from a home page: personal data (foaf:name, foaf:phone, etc.), relationships foaf:knows, rdfs:seeAlso ) 10 RDF Data online: Example 2/3 Digital Enterprise Research Institute www.deri.i e (i) directly by the publishers

(ii) by exporters, e.g. D2R and friends, RDFa exporters, etc. e.g. L3S RDF export of the DBLP citation index, using FUBs D2R (http://dblp.l3s.de/d2r/) Gives unique URIs to authors, documents, etc. on DBLP! E.g., http://dblp.l3s.de/d2r/resource/authors/Tim_Berners-Lee, http://dblp.l3s.de/d2r/resource/publications/journals/tplp/Berners-LeeCKSH08 Provides RDF version of all DBLP data and even a SPARQL query interface! 11 2. RDF can be described in terms of Ontologies and Rules allows Reasoning! Digital Enterprise Research Institute Every keynote at an event is a talk name(person1, "Scott Kelso ) Every talk given at AICS2010 is about AI If an event has a keynote, it is a speech given at the event Every AICS attendee not presenting a talk is attending the talk. Conference(aics2010). hasKeynote(aics2010, talk1). presentedBy(talk1,person1). Attendee(person1).

Attendee(person2). :hasKeynote rdfs:range :Talk . givenAt(E,T) :- hasKeynote(E,T). attendedBy(T,P) :- Attendee(P), not presentedBy(T,P). hasTopic(talk1,AI). :talk1 :hasTopic dbpedia:AI . 12 attentedBy(talk1, :talk1 :attentedBy person2). :person2 . ? www.deri.i e RDF Schema (RDFS) Web Ont. Lang. (OWL)

Rule Interchange Format (RIF) 2. RDF can be described in terms of Ontologies and Rules allows Reasoning! Digital Enterprise Research Institute OWLs theoretical foundation: Description Logics, SHOIN [Horrocks and Patel-Schneider, 2004] SROIQ [Horrocks et al. 2006] RIFs theoretical foundation: Logic programming, F-Logic, but also Datalog/Answer Set Programming, Deductive Databases (some RIF dialects allow negation as failure) RDF Schema: in essence in the intersection (but strictly speaking more liberal than Description Logics) 13 www.deri.i e 2. Structured queries over Web data Digital Enterprise Research Institute

www.deri.i e SPARQL = SQL look-and-feel query language for the Web allows us to ask structured queries such as: Give me names of people presenting AI or SemanticWeb talks SELECT ?Talk ?N { ?Talk :presentedBy ?P . ?P :name ?N { { ?Talk :hasTopic dbpedia:AI . } UNION { ?Talk :hasTopic dbpedia:Semantic_Web . } } } Unions of conjunctive queries, but also advanced features such as outer joins (NOT EXISTS), value filtering, etc. 14 How do the standards interplay? Digital Enterprise Research Institute Challenges:

Ontologies & Rules: OWL2 & RIF Querying Ontologies & Rules: SPARQL/OWL+RIF Data on the Web is NOT clean/consistent! Querying XML & RDF: XQuery & SPARQL Some of these challenges in Detail & current solutions to follow 15 www.deri.i e Ontologies and Rules: Digital Enterprise Research Institute Decidability:

OWL is decidable, Datalog with negation is decidable, but their union isnt. Nonmonotonicity: OWL/Description Logics are subsets of classical FO-Logic Rule Languages with Negation as failure (Answer Set Programming, Well-founded semantics) rely on nonclassical logics Cant arbitrarily mix RIF with OWL without trouble! 16 www.deri.i e presentedBy(talk1,person1). Attendee(person1). Attendee(person2). Approaches: Digital Enterprise Research Institute www.deri.i

e OWA vs (L)CWA: Has person2 presented talk1? givenAt(E,T) :- hasKeynote(E,T). attendedBy(T,P) :- Attendee(P), not presentedBy(T,P). Combinations of LP and DL still a vivid field of research Embedding LP and DL into common non-classical Logics: e.g. first-order autoepistemic Logics [deBruijn, Eiter, Polleres, Tompits et al. 2007,2010] Quantified Equilibrium Logics [deBruijn, Pearce,Polleres, Valverde, 2007, 2010] Defining decidable language fragments to combine: e.g. Horn-SHIQ, OWL2RL, DL-safe rules) which also means not yet mature for standardisation. 17

SPARQL & Ontologies: Digital Enterprise Research Institute www.deri.i e Similar problems: Decidability: Nonmonotonicity: 18 Conjunctive queries with non-distinguished variables for expressive DLs is an avtive field of research OWL2? Not yet known. [Glimm, Rudolph, KR2010] SPARQL has NOT EXISTS/OPTIONAL ~ similar negation as failure. Approaches: Digital Enterprise Research Institute www.deri.i

e Give me all talks that have a session chair? SELECT ?T { ?T :hasChair ?C } Do I need to know the actual chairs to answer this question? Two possible views on this query: Yes: Treat all query variables as distinguished (=output variables): Non-monotonic constructs on top not a problem for this approach SPARQL1.1 is currently exploring this route. No: in certain subsets of OWL this can be answered: Subset of OWL translatable to SQL: OWL2QL Subset of OWL translatable to extended versions of Datalog: Datalog [Cali et al. 2009]

BTW, query answering not only decidable but also tractable Problem: these two approaches are not compatible Is OWL suitable for Linked Data Digital Enterprise Research Institute www.deri.i e OWL DL Reasoning on data crawled from the Web almost certainly yields inconsistencies Assuming that the Semantic Web would be less messy than the HTML Web is very optimistic Example: Source A says: Document ( )

Source B says: Organisation ( ) Ontology C says: 20 Approaches Digital Enterprise Research Institute www.deri.i e OWL Reasoning on Web data needs to be scalable & noise tolerant Our approach

Sound but incomplete reasoning Use a robust/scalable fragment of OWL (OWL2RL) Exploit authority of Web documents Used in Sindice [Delbru et al. 2008], SWSE [Hogan et al. 2009] Alternatives? Para-consistent reasoning? RankingSources & Probabilistic Fuzzy Reasoning? 21 Bringing XML and RDF closer Digital Enterprise Research Institute

What if I want to translate RDF and OWL data back to XML/HTML ? 22 What to use? Custom Script? XSLT? SPARQL? www.deri.i e Why are XSLT, XQuery not enough? Digital Enterprise Research Institute Because RDF RDF/XML !!! representations 2) 1) many different RDF/XML and actually a lot of RDF data residing in RDF stores, accessible via SPARQL endpoints already, rather than in RDF/XML

23 www.deri.i e Our approach: XSPARQL (W3C submission, but not yet a standard) Digital Enterprise Research Institute www.deri.i e New query language but dont reinvent! XQuery + SPARQL = XSPARQL [Akhtar et al. 2008] { for $Person $Name from where { $Person foaf:name $Name } order by $Name return {for $FName from where { $Person foaf:knows

$Friend . $Person foaf:name $Name . $Friend foaf:name $Fname } return {$FName} } 24 } Conclusions & Outlook (Wheres the AI here?): Digital Enterprise Research Institute www.deri.i e Standards (RDF, OWL, SPARQL) are needed to enable structured querying about Web data. Wide adoption already: RDF is becoming a ubiquitous standard Lightweight OWL2 ontologies (FOAF,SIOC, GoodRelations, etc.) emerging

Lots of interesting datasets out there! (incl. Twitter, product descriptions/reviews) SPARQL becoming quite popular as well, RIF to be seen All these standards have clean formal foundations BUT: Still not enough data out there Still open KR problems on the border between standards (DL vs. LP vs. Query Languages) Data is not clean (needs AI methods! e.g.: para-consistent reasoning? Ontology matching, NLP, IM/IR,etc.) Query Optimisation in open federated environment is still barely understood, particularly

combined with ontological inference. Still a lot to be done 25 More challenges, interesting pointers: Digital Enterprise Research Institute www.deri.i e References: Articles on my Web page: http://www.polleres.net/ Axel Polleres. Semantic web technologies: From theory to standards. In 21st National Conference on Artificial Intelligence and Cognitive Science, Galway, Ireland, August 2010. Review paper http://www.polleres.net/publications/poll-2010aics.pdf New Journal Semantic Web Interoperability, Usability, Applicability, IOS Press http://www.semantic-webjournal.net/ will have some very interesting position papers in its first issue, e.g.:

S. Auer and J. Lehmann. Making the Web a Data Washing Machine - Creating Knowledge out of Interlinked Data. SWJ, accepted for publication, 2010. http://www.semantic-web-journal.net/content/new-submission-towards-creating-knowledge-out-interlinked-data P. Hitzler, F. van Harmelen A Reasonable Semantic Web. SWJ, accepted for publication, 2010 http://www.semantic-web-journal.net/content/new-submission-reasonable-semantic-web A. Polleres, A. Hogan, A. Harth, S. Decker. Can we ever catch up with the Web? SWJ, accepted for publication, 2010. 26 http://www.semantic-web-journal.net/content/new-submission-can-we-ever-catch-web

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