RQL: a declarative query language for RDF

Real-scale Semantic Web applications, such as Knowledge Portals and E-Marketplaces, require the management of large volumes of metadata, i.e., information describing the available Web content and services. Better knowledge about their meaning, usage, accessibility or quality will considerably facilitate an automated processing of Web resources. The Resource Description Framework (RDF) enables the creation and exchange of metadata as normal Web data. Although voluminous RDF descriptions are already appearing, sufficiently expressive declarative languages for querying both RDF descriptions and schemas are still missing. In this paper, we propose a new RDF query language called RQL. It is a typed functional language (a la OQL) and relies on a formal model for directed labeled graphs permitting the interpretation of superimposed resource descriptions by means of one or more RDF schemas. RQL adapts the functionality of semistructured/XML query languages to the peculiarities of RDF but, foremost, it enables to uniformly query both resource descriptions and schemas. We illustrate the RQL syntax, semantics and typing system by means of a set of example queries and report on the performance of our persistent RDF Store employed by the RQL interpreter.

[1]  C. M. Sperberg-McQueen,et al.  eXtensible Markup Language (XML) 1.0 (Second Edition) , 2000 .

[2]  Alin Deutsch,et al.  A Query Language for XML , 1999, Comput. Networks.

[3]  Michael Kifer,et al.  F-logic: a higher-order language for reasoning about objects, inheritance, and scheme , 1989, SIGMOD '89.

[4]  Vassilis Christophides,et al.  On Storing Voluminous RDF Descriptions: The Case of Web Portal Catalogs , 2001, WebDB.

[5]  Dan Brickley,et al.  Resource Description Framework (RDF) Model and Syntax Specification , 2002 .

[6]  Jennifer Widom,et al.  The Lorel query language for semistructured data , 1997, International Journal on Digital Libraries.

[7]  Serge Abiteboul,et al.  Foundations of Databases , 1994 .

[8]  Laks V. S. Lakshmanan,et al.  Querying network directories , 1999, SIGMOD '99.

[9]  Matthias Jarke,et al.  Telos: representing knowledge about information systems , 1990, TOIS.

[10]  Jeffrey D. Ullman,et al.  MedMaker: a mediation system based on declarative specifications , 1996, Proceedings of the Twelfth International Conference on Data Engineering.

[11]  Donald D. Chamberlin,et al.  XQuery: a query language for XML , 2003, SIGMOD '03.

[12]  David Jordan,et al.  The Object Database Standard: ODMG 2.0 , 1997 .

[13]  Sophie Cluet,et al.  Your mediators need data conversion! , 1998, SIGMOD '98.

[14]  Laks V. S. Lakshmanan,et al.  SchemaSQL - A Language for Interoperability in Relational Multi-Database Systems , 1996, VLDB.

[15]  Dan Suciu,et al.  Data on the Web: From Relations to Semistructured Data and XML , 1999 .

[16]  Dan Suciu,et al.  STRUDEL: a Web site management system , 1997, SIGMOD '97.

[17]  Laks V. S. Lakshmanan,et al.  On Bounding-Schemas for LDAP Directories , 2000, EDBT.

[18]  Alexander Borgida,et al.  Efficient management of transitive relationships in large data and knowledge bases , 1989, SIGMOD '89.

[19]  Guido Moerkotte,et al.  Querying documents in object databases , 1997, International Journal on Digital Libraries.

[20]  Letizia Tanca,et al.  XML-GL: A Graphical Language for Querying and Restructuring XML Documents , 1999, SEBD.

[21]  Daniela Florescu,et al.  A Performance Evaluation of Alternative Mapping Schemes for Storing XML Data in a Relational Database , 1999 .

[22]  Luca Cardelli,et al.  A Semantics of Multiple Inheritance , 1984, Inf. Comput..

[23]  Vassilis Christophides,et al.  Querying RDF Descriptions for Community Web Portals , 2001, BDA.

[24]  C. M. Sperberg-McQueen,et al.  Extensible Markup Language (XML) , 1997, World Wide Web J..

[25]  Vassilis Christophides,et al.  The ICS-FORTH RDFSuite: Managing Voluminous RDF Description Bases , 2001, SemWeb.

[26]  Dan Suciu,et al.  Programming Constructs for Unstructured Data , 1995, DBPL.

[27]  Lois M. L. Delcambre,et al.  Models for Superimposed Information , 1999, ER.

[28]  Lois M. L. Delcambre,et al.  Superimposed Information for the Internet , 1999, WebDB.

[29]  Daniela Florescu,et al.  Quilt: An XML Query Language for Heterogeneous Data Sources , 2000, WebDB.

[30]  Nicolás Marín,et al.  Review of Data on the Web: from relational to semistructured data and XML by Serge Abiteboul, Peter Buneman, and Dan Suciu. Morgan Kaufmann 1999. , 2003, SGMD.

[31]  Patrick Hayes,et al.  Rdf Model Theory W3c Working Draft @@@@@ Status of This Document , 2001 .

[32]  Massimo Marchiori,et al.  Query + Metadata + Logic = Metalog , 1998, QL.

[33]  Vassilis Christophides,et al.  On wrapping query languages and efficient XML integration , 2000, SIGMOD '00.

[34]  Serge Abiteboul,et al.  From structured documents to novel query facilities , 1994, SIGMOD '94.

[35]  Michael Kifer,et al.  Querying object-oriented databases , 1992, SIGMOD '92.

[36]  Vassilis Christophides,et al.  On wrapping query languages and efficient XML integration , 2000, SIGMOD 2000.

[37]  Dimitris Plexousakis,et al.  SEMANTICAL AND ONTOLOGICAL CONSIDERATIONS IN TELOS: A LANGUAGE FOR KNOWLEDGE REPRESENTATION DIMITRIS PLEXOUSAKIS , 1993, Comput. Intell..

[38]  Arvind Malhotra,et al.  Xml schema part 2: datatypes , 1999 .

[39]  Kenneth A. Ross,et al.  Noodle: A Language for Declarative Querying in an Object-Oriented Database , 1993, DOOD.

[40]  Guido Moerkotte,et al.  Evaluating queries with generalized path expressions , 1996, SIGMOD '96.