NautiLOD: A Formal Language for the Web of Data Graph

The Web of Linked Data is a huge graph of distributed and interlinked datasources fueled by structured information. This new environment calls for formal languages and tools to automatize navigation across datasources (nodes in such graph) and enable semantic-aware and Web-scale search mechanisms. In this article we introduce a declarative navigational language for the Web of Linked Data graph called NautiLOD. NautiLOD enables one to specify datasources via the intertwining of navigation and querying capabilities. It also features a mechanism to specify actions (e.g., send notification messages) that obtain their parameters from datasources reached during the navigation. We provide a formalization of the NautiLOD semantics, which captures both nodes and fragments of the Web of Linked Data. We present algorithms to implement such semantics and study their computational complexity. We discuss an implementation of the features of NautiLOD in a tool called swget, which exploits current Web technologies and protocols. We report on the evaluation of swget and its comparison with related work. Finally, we show the usefulness of capturing Web fragments by providing examples in different knowledge domains.

[1]  Jürgen Umbrich,et al.  A Comparison of Federation over SPARQL Endpoints Frameworks , 2013, KESW.

[2]  Alberto O. Mendelzon,et al.  Querying the World Wide Web , 1997, International Journal on Digital Libraries.

[3]  Claudio Gutiérrez,et al.  Semantic navigation on the web of data: specification of routes, web fragments and actions , 2011, WWW.

[4]  Krys J. Kochut,et al.  SPARQLeR: Extended Sparql for Semantic Association Discovery , 2007, ESWC.

[5]  Gerhard Weikum,et al.  Database Foundations for Scalable RDF Processing , 2011, Reasoning Web.

[6]  Tim Berners-Lee,et al.  Linked data , 2020, Semantic Web for the Working Ontologist.

[7]  Timothy W. Finin,et al.  Swoogle: a search and metadata engine for the semantic web , 2004, CIKM '04.

[8]  Carlos A. Hurtado,et al.  Edinburgh Research Explorer Expressive Languages for Path Queries over Graph-Structured Data , 2012 .

[9]  Enrico Motta,et al.  Watson, more than a Semantic Web search engine , 2011, Semantic Web.

[10]  Eyal Oren,et al.  Extending Faceted Navigation for RDF Data , 2006, SEMWEB.

[11]  Christian Bizer,et al.  Executing SPARQL Queries over the Web of Linked Data , 2009, SEMWEB.

[12]  Heiko Paulheim,et al.  Adoption of the Linked Data Best Practices in Different Topical Domains , 2014, SEMWEB.

[13]  Lydia B. Chilton,et al.  Tabulator: Exploring and Analyzing linked data on the Semantic Web , 2006 .

[14]  Claudio Gutiérrez,et al.  Knowledge Maps of Web Graphs , 2014, KR.

[15]  Jürgen Umbrich,et al.  Querying over Federated SPARQL Endpoints - A State of the Art Survey , 2013, ArXiv.

[16]  Daniel Schwabe,et al.  Explorator: A tool for exploring RDF data through direct manipulation , 2009, LDOW.

[17]  Peter T. Wood,et al.  Query languages for graph databases , 2012, SGMD.

[18]  Katja Hose,et al.  FedX: Optimization Techniques for Federated Query Processing on Linked Data , 2011, SEMWEB.

[19]  Paul T. Groth,et al.  Using provenance in the Semantic Web , 2011, J. Web Semant..

[20]  Ioana Manolescu,et al.  Active XML: Peer-to-Peer Data and Web Services Integration , 2002, VLDB.

[21]  Claudio Gutierrez,et al.  Survey of graph database models , 2008, CSUR.

[22]  Marcelo Arenas,et al.  Semantics and complexity of SPARQL , 2006, TODS.

[23]  P. Wadler.  Two semantics for XPath , 2000 .

[24]  Michael Hausenblas,et al.  Describing linked datasets with the VoID vocabulary , 2011 .

[25]  Olaf Hartig,et al.  Zero-Knowledge Query Planning for an Iterator Implementation of Link Traversal Based Query Execution , 2011, ESWC.

[26]  Gerhard Weikum,et al.  Deep answers for naturally asked questions on the web of data , 2012, WWW.

[27]  Steffen Stadtmüller,et al.  Data-Fu: a language and an interpreter for interaction with read/write linked data , 2013, WWW.

[28]  Alexandra Poulovassilis,et al.  RDFTL : An Event-Condition-Action Language for RDF , 2004 .

[29]  Alberto O. Mendelzon,et al.  Database techniques for the World-Wide Web: a survey , 1998, SGMD.

[30]  Jürgen Umbrich,et al.  Link traversal querying for a diverse Web of Data , 2014, Semantic Web.

[31]  Marcelo Arenas,et al.  nSPARQL: A Navigational Language for RDF , 2008, SEMWEB.

[32]  Sergey Brin,et al.  The Anatomy of a Large-Scale Hypertextual Web Search Engine , 1998, Comput. Networks.

[33]  M. W. Shields.  An Introduction to Automata Theory , 1988 .

[34]  Jeffrey D. Ullman,et al.  Introduction to Automata Theory, Languages and Computation , 1979 .

[35]  Jean-François Baget,et al.  Extending SPARQL with regular expression patterns (for querying RDF) , 2009, J. Web Semant..

[36]  Claudio Gutiérrez,et al.  The Map Generator Tool , 2014, International Semantic Web Conference.

[37]  Daniel Schwabe,et al.  Support for Reusable Explorations of Linked Data in the Semantic Web , 2012, SeCO Book.

[38]  Jürgen Umbrich,et al.  LDspider: An Open-source Crawling Framework for the Web of Linked Data , 2010, SEMWEB.

[39]  Lynda Hardman,et al.  /facet: A Browser for Heterogeneous Semantic Web Repositories , 2006, SEMWEB.

[40]  Chang Liu,et al.  Term rewriting and all that , 2000, SOEN.

[41]  Tom Heath,et al.  Linked Data: Evolving the Web into a Global Data Space , 2011, Linked Data.

[42]  Eyal Oren,et al.  Sindice.com: a document-oriented lookup index for open linked data , 2008, Int. J. Metadata Semant. Ontologies.

[43]  M. Tamer Özsu,et al.  Reachable subwebs for traversal-based query execution , 2014, WWW '14 Companion.

[44]  Jeremy J. Carroll,et al.  Resource description framework (rdf) concepts and abstract syntax , 2003 .

[45]  Jürgen Umbrich,et al.  Data summaries for on-demand queries over linked data , 2010, WWW '10.

[46]  Peter Haase,et al.  An evaluation of approaches to federated query processing over linked data , 2010, I-SEMANTICS '10.

[47]  Serge Abiteboul,et al.  Queries and computation on the web , 1997, Theor. Comput. Sci..

[48]  Anthony Widjaja Lin,et al.  Expressive Languages for Path Queries over Graph-Structured Data , 2012, TODS.

[49]  Jesse Weaver,et al.  Facebook Linked Data via the Graph API , 2013, Semantic Web.

[50]  Sebastian Schaffert,et al.  The linked media framework: integrating and interlinking enterprise media content and data , 2012, I-SEMANTICS '12.

[51]  Steven J. DeRose,et al.  XML Path Language (XPath) Version 1.0 , 1999 .

[52]  Claudio Gutiérrez,et al.  The swget portal: Navigating and acting on the web of linked data , 2014, J. Web Semant..

[53]  Ulf Leser,et al.  Querying Distributed RDF Data Sources with SPARQL , 2008, ESWC.

[54]  Tim Furche,et al.  A RPL through RDF: Expressive Navigation in RDF Graphs , 2010, RR.