LDQL: A Query Language for the Web of Linked Data

The Web of Linked Data is composed of tons of RDF documents interlinked to each other forming a huge repository of distributed semantic data. Effectively querying this distributed data source is an important open problem in the Semantic Web area. In this paper, we propose LDQL, a declarative language to query Linked Data on the Web. One of the novelties of LDQL is that it expresses separately ii??patterns that describe the expected query result, and iiWeb navigation paths that select the data sources to be used for computing the result. We present a formal syntax and semantics, prove equivalence rules, and study the expressiveness of the language. In particular, we show that LDQL is strictly more expressive than the query formalisms that have been proposed previously for Linked Data on the Web. The high expressiveness allows LDQL to define queries for which a complete execution is not computationally feasible over the Web. We formally study this issue and provide a syntactic sufficient condition to avoid this problem; queries satisfying this condition are ensured to have a procedure to be effectively evaluated over the Web of Linked Data.

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

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

[3]  Jorge Pérez,et al.  Simple and Efficient Minimal RDFS , 2009, J. Web Semant..

[4]  Tok Wang Ling,et al.  A Conceptual Model and Rule-Based Query Language for HTML , 2001, World Wide Web.

[5]  K. Selçuk Candan,et al.  WebDB: A System for Querying Semi-structured Data on the Web , 2002, J. Vis. Lang. Comput..

[6]  Jorge Pérez,et al.  LDQL: A Query Language for the Web of Linked Data (Extended Version) , 2016, J. Web Semant..

[7]  Jürgen Umbrich,et al.  Searching and browsing Linked Data with SWSE: The Semantic Web Search Engine , 2011, J. Web Semant..

[8]  Jeremy J. Carroll,et al.  OWL 2 Web Ontology Language RDF-Based Semantics , 2009 .

[9]  Olaf Hartig,et al.  An Overview on Execution Strategies for Linked Data Queries , 2013, Datenbank-Spektrum.

[10]  S. Hadjiefthymiades,et al.  Hypertext Transfer Protocol (HTTP) , 1996 .

[11]  Sebastian Speiser,et al.  On Completeness Classes for Query Evaluation on Linked Data , 2012, AAAI.

[12]  Olaf Hartig,et al.  SPARQL with property paths on the Web , 2017, Semantic Web.

[13]  Jürgen Umbrich,et al.  Comparing data summaries for processing live queries over Linked Data , 2011, World Wide Web.

[14]  Roy T. Fielding,et al.  Uniform Resource Identifier (URI): Generic Syntax , 2005, RFC.

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

[16]  Alberto O. Mendelzon,et al.  GraphLog: a visual formalism for real life recursion , 1990, PODS '90.

[17]  Marcelo Arenas,et al.  Counting beyond a Yottabyte, or how SPARQL 1.1 property paths will prevent adoption of the standard , 2012, WWW.

[18]  Alberto O. Mendelzon,et al.  Formal models of Web queries , 1997, Inf. Syst..

[19]  Bertram Ludäscher,et al.  On a Declarative Semantics for Web Queries , 1997, DOOD.

[20]  Paolo Merialdo,et al.  Efficient Queries over Web Views , 2002, IEEE Trans. Knowl. Data Eng..

[21]  Claudio Gutiérrez,et al.  NautiLOD: A Formal Language for the Web of Data Graph , 2015, TWEB.

[22]  Olaf Hartig.  LDQL: A Language for Linked Data Queries , 2015, AMW.

[23]  Peter F. Patel-Schneider,et al.  OWL 2 Web Ontology Language , 2009 .

[24]  Jim Webber,et al.  A programmatic introduction to Neo4j , 2018, SPLASH '12.

[25]  D Manyu,et al.  Hypertext transfer protocol , 2009 .

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

[27]  Lynn Andrea Stein,et al.  Squeal: a structured query language for the Web , 2000, Comput. Networks.

[28]  Miao Liu,et al.  Structure-Based Queries over the World Wide Web , 1998, ER.

[29]  Olaf Hartig,et al.  A Context-Based Semantics for SPARQL Property Paths over the Web (Extended Version) , 2015, ESWC.

[30]  David Konopnicki,et al.  W3QS: A Query System for the World-Wide Web , 1995, VLDB.

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

[32]  Laks V. S. Lakshmanan,et al.  A declarative language for querying and restructuring the Web , 1996, Proceedings RIDE '96. Sixth International Workshop on Research Issues in Data Engineering.

[33]  Günter Ladwig,et al.  Linked Data Query Processing Strategies , 2010, SEMWEB.

[34]  Moshe Y. Vardi.  The complexity of relational query languages (Extended Abstract) , 1982, STOC '82.

[35]  David Konopnicki,et al.  Information gathering in the World-Wide Web: the W3QL query language and the W3QS system , 1998, TODS.

[36]  Óscar Corcho,et al.  Semantics and Optimization of the SPARQL 1.1 Federation Extension , 2011, ESWC.

[37]  Olaf Hartig,et al.  SPARQL for a Web of Linked Data: Semantics and Computability (Extended Version) , 2012, ESWC.

[38]  Ruben Verborgh,et al.  Triple Pattern Fragments: A low-cost knowledge graph interface for the Web , 2016, J. Web Semant..

[39]  Walter Goralski.  Chapter 26 – Hypertext Transfer Protocol , 2017 .

[40]  Alberto O. Mendelzon,et al.  Visualizing the World Wide Web , 1996, AVI '96.

[41]  Luciano Serafini,et al.  Querying the Web of Data: A Formal Approach , 2009, ASWC.

[42]  Sergio Greco,et al.  Querying Graph Databases , 2000, EDBT.

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

[44]  Marcelo Arenas,et al.  On the Semantics of SPARQL , 2009, Semantic Web Information Management.

[45]  Alberto O. Mendelzon,et al.  Applications of a Web Query Language , 1997, Comput. Networks.

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

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

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