RQL: a declarative query language for RDF

ABSTRACT

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.

REFERENCES

• 1: Serge Abiteboul , Peter Buneman , Dan Suciu, Data on the Web: from relations to semistructured data and XML, Morgan Kaufmann Publishers Inc., San Francisco, CA, 1999
• 2: S. Abiteboul, S. Cluet, V. Christophides, T. Milo, G. Moerkotte, and J. Siméon. Querying Documents in Object Databases. International Journal on Digital Libraries, 1(1):5--18, April 1997.
• 3: Serge Abiteboul , Richard Hull , Victor Vianu, Foundations of Databases: The Logical Level, Addison-Wesley Longman Publishing Co., Inc., Boston, MA, 1995
• 4: S. Abiteboul, D. Quass, J. McHugh, J. Widom, and J. Wiener. The Lorel Query Language for Semistructured Data. International Journal on Digital Libraries, 1(1):68--88, April 1997.
• 5: R. Agrawal , A. Borgida , H. V. Jagadish, Efficient management of transitive relationships in large data and knowledge bases, Proceedings of the 1989 ACM SIGMOD international conference on Management of data, p.253-262, June 1989, Portland, Oregon, United States
• 6: S. Alexaki, G. Karvounarakis, V. Christophides, D. Plexousakis, and K. Tolle. The ICS-FORTH RDFSuite: Managing Voluminous RDF Description Bases. In 2nd International Workshop on the Semantic Web, pages 1--13, Hong Kong, 2001. Available at 139.91.183.30:9090/RDF/publications/semweb2001.pdf.
• 7: S. Alexaki, G. Karvounarakis, V. Christophides, D. Plexousakis, and K. Tolle. On Storing Voluminous RDF descriptions: The case of Web Portal Catalogs. In 4th International Workshop on the Web and Databases (WebDB), Santa Barbara, CA, 2001. Available at 139.91.183.30:9090/RDF/publications/-webdb2001.pdf.
• 8: Sihem Amer-Yahia , H. V. Jagadish , Laks V. S. Lakshmanan , Divesh Srivastava, On Bounding-Schemas for LDAP Directories, Proceedings of the 7th International Conference on Extending Database Technology: Advances in Database Technology, p.287-301, March 27-31, 2000
• 9: G. Beged-Dov, D. Brickley , R. Dornfest , I. Davis , L. Dodds , J. Eisenzopf , D. Galbraith, R. V. Guha , K. MacLeod , E. Miller , A. Swartz and E. van der Vlist Rich Site Summary Specification Protocol (RSS 1.0). Internet Draft, August 2000.
• 10: T. Berners-Lee, J. Hendler, and O. Lassila. The Semantic Web. Scientific American, May 2001.
• 11: T. Bray, J. Paoli, and C. M. Sperberg-McQueen. Extensible markup language (XML) 1.0. W3C Recommendation, February 1998. Available at www.w3.org/TR/REC-xml/.
• 12: D. Brickley and R. V. Guha. Resource Description Framework (RDF) Schema Specification 1.0, W3C Candidate Recommendation. Technical report, 2000.
• 13: Peter Buneman , Susan B. Davidson , Dan Suciu, Programming Constructs for Unstructured Data, Proceedings of the Fifth International Workshop on Database Programming Languages, p.12, September 06-08, 1995
• 14: Luca Cardelli, A semantics of multiple inheritance, Information and Computation, v.76 n.2-3, p.138-164, February/March 1988 [doi>10.1016/0890-5401(88)90007-7]
• 15: R. G. G. Cattell , Douglas K. Barry , Mark Berler , Jeff Eastman , David Jordan , Craig Russell , Olaf Schadow , Torsten Stanienda , Fernando Velez, The object data standard: ODMG 3.0, Morgan Kaufmann Publishers Inc., San Francisco, CA, 2000
• 16: Stefano Ceri , Sara Comai , Ernesto Damiani , Piero Fraternali , Stefano Paraboschi , Letizia Tanca, XML-GL: a graphical language for querying and restructuring XML documents, Proceeding of the eighth international conference on World Wide Web, p.1171-1187, May 1999, Toronto, Canada
• 17: D. Chamberlin, D. Florescu, J. Robie, J. Simeon, and M. Stefanescu. XQuery: A Query Language for XML. Working draft, World Wide Web Consortium, June 2001. Available at www.w3.org/TR/xquery/.
• 18: V. Christophides , S. Abiteboul , S. Cluet , M. Scholl, From structured documents to novel query facilities, Proceedings of the 1994 ACM SIGMOD international conference on Management of data, p.313-324, May 24-27, 1994, Minneapolis, Minnesota, United States
• 19: Vassilis Christophides , Sophie Cluet , Guido Moerkotte, Evaluating queries with generalized path expressions, Proceedings of the 1996 ACM SIGMOD international conference on Management of data, p.413-422, June 04-06, 1996, Montreal, Quebec, Canada
• 20: Vassilis Christophides , Sophie Cluet , Jérǒme Simèon, On wrapping query languages and efficient XML integration, Proceedings of the 2000 ACM SIGMOD international conference on Management of data, p.141-152, May 15-18, 2000, Dallas, Texas, United States
• 21: Sophie Cluet , Claude Delobel , Jérǒme Siméon , Katarzyna Smaga, Your mediators need data conversion!, Proceedings of the 1998 ACM SIGMOD international conference on Management of data, p.177-188, June 01-04, 1998, Seattle, Washington, United States
• 22: The UDDI community. Universal description, discovery, and integration (uddi v2.0). Available at www.uddi.org/, October 2001.
• 23: Donald D. Chamberlin , Jonathan Robie , Daniela Florescu, Quilt: An XML Query Language for Heterogeneous Data Sources, Selected papers from the Third International Workshop WebDB 2000 on The World Wide Web and Databases, p.1-25, May 18-19, 2000
• 24: S. Decker, D. Brickley, J. Saarela, and J. Angele. A query and inference service for RDF. In W3C QL Workshop, 1998.
• 25: Lois M. L. Delcambre , David Maier, Models for Superimposed Information, Proceedings of the Workshops on Evolution and Change in Data Management, Reverse Engineering in Information Systems, and the World Wide Web and Conceptual Modeling, p.264-280, November 15-18, 1999
• 26: Alin Deutsch , Mary Fernandez , Daniela Florescu , Alon Levy , Dan Suciu, A query language for XML, Proceeding of the eighth international conference on World Wide Web, p.1155-1169, May 1999, Toronto, Canada
• 27: The ebXML community. Enabling a global electronic market (ebxml v.1.4). Available at www.ebxml.org/, February 2001.
• 28: Mary Fernandez , Daniela Florescu , Jaewoo Kang , Alon Levy , Dan Suciu, STRUDEL: a Web site management system, Proceedings of the 1997 ACM SIGMOD international conference on Management of data, p.549-552, May 11-15, 1997, Tucson, Arizona, United States
• 29: R. Fikes. DAML+OIL query language proposal, August 2001. Available at www.daml.org/-listarchive/joint-committee/-0572.html.
• 30: D. Florescu and D. Kossmann. A performance evaluation of alternative mapping schemes for storing xml data in a relational database. Technical Report 3680, INRIA Rocquencourt, France, 1999.
• 31: P. Hayes. RDF Model Theory. W3C Working Draft, September 2001.
• 32: ICS-FORTH. The ICS-FORTH RDFSuite web site. Available at 139.91.183.30:9090/RDF, March 2002.
• 33: ISO. Information Processing-Text and Office Systems- Standard Generalized Markup Language (SGML). ISO 8879, 1986.
• 34: H. V. Jagadish , Laks V. S. Lakshmanan , Tova Milo , Divesh Srivastava , Dimitra Vista, Querying network directories, Proceedings of the 1999 ACM SIGMOD international conference on Management of data, p.133-144, May 31-June 03, 1999, Philadelphia, Pennsylvania, United States
• 35: G. Karvounarakis, V. Christophides, D. Plexousakis, and S. Alexaki. Querying RDF Descriptions for Community Web Portals. In BDA'2001 (17iemes Journees Bases de Donnees Avances - French Conference on Databases), pages 133--144, Agadir, Morocco, 2001. Available at 139.91.183.30:9090/RDF/publications/bda2001.pdf.
• 36: Michael Kifer , Won Kim , Yehoshua Sagiv, Querying object-oriented databases, Proceedings of the 1992 ACM SIGMOD international conference on Management of data, p.393-402, June 02-05, 1992, San Diego, California, United States
• 37: Michael Kifer , Georg Lausen, F-logic: a higher-order language for reasoning about objects, inheritance, and scheme, Proceedings of the 1989 ACM SIGMOD international conference on Management of data, p.134-146, June 1989, Portland, Oregon, United States
• 38: Laks V. S. Lakshmanan , Fereidoon Sadri , Iyer N. Subramanian, SchemaSQL - A Language for Interoperability in Relational Multi-Database Systems, Proceedings of the 22th International Conference on Very Large Data Bases, p.239-250, September 03-06, 1996
• 39: O. Lassila and R. Swick. Resource Description Framework (RDF) Model and Syntax Specification, W3C Recommendation. Technical report, , 1999.
• 40: J. Liljegren. Description of an RDF database implementation. Available at www-db.stanford.edu/~melnik/rdf/db-jonas.html.
• 41: D. Maier and L. Delcambre. Superimposed information for the internet. In ACM SIGMOD Workshop on The Web and Databases Philadelphia, Pennsylvania, June 3-4, pages 1--9, 1999.
• 42: M. Maloney and A. Malhotra. XML schema part 2: Datatypes. W3C Candidate Recommendation, October 2000. Available at www.w3.org/TR/xmlschema-2/.
• 43: M. Marchiori and J. Saarela. Query + metadata + logic = metalog. In W3C QL Workshop, 1998.
• 44: S. Melnik. Storing RDF in a relational database. Available at www-db.stanford.edu/~melnik/rdf/db.html.
• 45: L. Miller. RDF Query using SquishQL. Available at swordfish.rdfweb.org/rdfquery/, 2001.
• 46: I. S. Mumick and K. A. Ross. Noodle: A Language for Declarative Querying in an Object-Oriented Database. In Proceedings of International Conference on Deductive and Object-Oriented Databases (DOOD), pages 360--378, Phoenix, Arizona, December 1993.
• 47: John Mylopoulos , Alex Borgida , Matthias Jarke , Manolis Koubarakis, Telos: representing knowledge about information systems, ACM Transactions on Information Systems (TOIS), v.8 n.4, p.325-362, Oct. 1990 [doi>10.1145/102675.102676]
• 48: Yannis Papakonstantinou , Hector Garcia-Molina , Jeffrey D. Ullman, MedMaker: A Mediation System Based on Declarative Specifications, Proceedings of the Twelfth International Conference on Data Engineering, p.132-141, February 26-March 01, 1996
• 49: D. Plexousakis. Semantical and Ontological Considerations in Telos: a Language for Knowledge Representation. Computational Intelligence, 9(1):41--72, 1993.
• 50: Some proposed RDF APIs. GINF: www-db.stanford.edu/~melnik/rdf/api.html, RADIX: www.mailbase.ac.uk/lists/rdf-dev/1999-06/0002.html, Netscape/Mozilla: lxr.mozilla.org/seamonkey/source/rdf/base/idl/, RDF4J: www.alphaworks.ibm.com/formula/rdfxml/, Jena: www-uk.hpl.hp.com/people/bwm/RDF/jena, Redland: www.redland.opensource.ac.uk/docs/api.
• 51: A. Seaborne. RDQL: A Data Oriented Query Language for RDF Models. Available at www-uk.hpl.hp.com/people/afs/RDQL/, 2001.
• 52: M. Sintek and S. Decker. RDF Query and Transformation Language. Available at www.dfki.uni-kl.de/frodo/triple/, August 2001.
• 53: H. S. Thompson, D. Beech, M. Maloney, and N. Mendelsohn. XML schema part 1: Structures. W3C Candidate Recommendation, October 2000. Available at www.w3.org/TR/xmlschema-1/.
• 54: F. van Harmelen, P. Patel-Schneider, and I. Horrocks. Reference description of the DAML+OIL ontology markup language. Available at www.daml.org/2001/03/reference.html, March 2001.
• 55: Web service description language (WSDL). Available at www106.ibm.com/developerworks/library/ws-rdf, 2000.

INDEX TERMS

Primary Classification:
  H. Information Systems
  H.2 DATABASE MANAGEMENT
      H.2.3 Languages
          Subjects: Query languages

General Terms:
Languages, Management, Standardization