27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU1 Semantic Query Languages Atilla ELÇİ Dept. of Computer Engineering Eastern Mediterranean University

27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU2 What is Query Language?  Webopedia: A specialized language for requesting information from a database. For example, the query SELECT ALL WHERE age > 30 AND name = "Smith" Webopedialanguagedatabasequery  requests all records in which the name- field is "Smith" and the Age field has a value greater than 30. The de facto standard for query languages is SQL.records fieldde facto standardSQL

27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU3 Shortcomings of Current Query Language Technology  Query construction: Syntactic units such as keywords/terms are used. Polysemy: multiple meanings Query ambiguity: # of keywords used per query (circa 2000): 2.2!  Lack of semantics: Inability to handle synonymy & polisemy Missed semantic links  Lack of context: Missing the context to disambiguate the user’s query.  Presentation of results: Often too many results  Managing heterogeneity: Providing a coherent view of diverse sources and types of information: very difficult and unsatisfactory at the best.  Lots of data but lacking information!  High recall but low precision!

Shortcoming 2  Difficult for ordinary end user  DB schemas change over time even though the data remains unchanged  Addition of a new set of data or archiving existing data may also result in schema changes ==> These non-semantic changes imply changes in queries therefore updates on IS relying on such queries. [Yuan & Jones] 27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU4

Semantic Access to RDB Data  Most data is kept in RDB sets due to various resons  Some challenges of semantic access to existing RDB data: Lack of explicit ontology of RDB data Mapping:  the semantic model (ontology) to the underlying data model; or  the semantic query primitives to the relational query primitives  “In order to successfully push down the semantic query evaluation as much as possible into a RDB query engine, a generic mapping structure needs to be developed between ontologies and relational data models and theoretical foundation needs to be built between the semantic query formalisms and the relational calculus/algebra.” Result transformation: Query answer transformation: converting query answers out of the RDB engine into an instantiation of ontology:  How to formulate the URI for each instance?  how to preserve the intermediate query answers efficiently? Performance 27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU5

27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU6 Advantages of Semantic Web Technology (Retrofitted for Semantic Query Language Technology)  Resolving shortcomings of the current query languages by: Exploiting machine-processable metadata Using ontological concepts to define queries Using semantic relations in defining queries Providing information not simply data  Future search engines must rely on “information-centric” approach including semantic query languages rather than document-centric one in order to seek: Relevant sections not simply documents Digest of info from several docs/sections

.QL  An object-oriented query language used to retrieve data from relational database management systems. [Wikipedia]database management systemsWikipedia .QL language reference..QL language reference  A private initiative of Semmle Limited.Semmle Limited 27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU7

Library of Congress’ CQL  CQL: Contextual Query Language (SRU Version 1.2 Specifications)SRU Version 1.2 Specifications Note its query syntax and some examples. Note its BNF definition. 27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU8

OASIS Core Standards  OASIS Cover Pages: process history of generating XML query languages: XQuery and its lesser brother XPath in the XSLT technology line for full-text search over XML documents.Cover Pages 27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU9

XQuery: XML Query Language  XQuery is a query language (with some programming language features) that is designed to query collections of XML data. It is semantically similar to SQL. [Wikipedia]query languageprogramming language XMLsemantically similarSQLWikipedia  XQuery is a functional language comprised of several kinds of expressions that can be nested and composed with full generality.  XQuery tutorial by DonChamberlin (an editor of XQuery language specifications): XQuery: An XML query language. In IBM Systems Journal, Vol 41, No 4, 2002, pp: XQuery tutorial Take note of the complexity of syntax, For example: even simple cases like Q7 & Q8. And, see sample function definitions.  Current: XQuery 1.0 and XPath 2.0 Full-Text 1.0 as W3C Working Draft dated 18 May 2007.W3C Working Draft dated 18 May /04/08 rev 29/4/08CmpE 588 Spring 2008 EMU10

RDF Query Language  A RDF query language is a computer language able to retrieve and manipulate data stored in Resource Description Framework format. Resource Description Framework  Check Wikipedia entry for links to a list of RDF query languages, such as, DQL, N3QL, R- DEVICE, RDFQ, RDQ, RDQL, RQL/RVL, SeRQL, Versa, XUL, and Adenine.Wikipedia entry  SPARQL is now a defacto standard. 27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU11

W3C SPARQL  SPARQL (pronounced "sparkle" [1] ) is an RDF query language. [Wikipedia]sparkle [1]RDF query languageWikipedia  Its name is a recursive acronym that stands for SPARQL Protocol and RDF Query Language  Standardized by W3C RDF Data Access Working Group.W3C RDF Data Access Working Group  SPARQL Protocol for RDF: Protocol for RDF  It uses WSDL 2.0 to describe a means for conveying SPARQL queries to an SPARQL query processing service and returning the query results to the entity that requested them.WSDL 2.0  SPARQL Query Language for RDFQuery Language for RDF W3C Recommendation 15 January 2008 Defines the syntax and semantics of SPARQL query language for RDF. 27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU12

SPARQL Query Language for RDFQuery Language for RDF  Can express queries across diverse data sources, such as stored natively as RDF or viewed as RDF via middleware.  Can query required and optional graph patterns, their conjunctions and disjunctions.  Supports extensible value testing and constraining queries by source RDF graph.  The results of SPARQL queries can be results sets or RDF graphs.  Examples: Example in Wikipedia entry.Wikipedia Sect. 1 & 2 in W3C Recommendation 15 January 2008W3C Recommendation 15 January /04/08 rev 29/4/08CmpE 588 Spring 2008 EMU13

SPARQL Software  ESW Wiki Entry: SparqlImplementationsSparqlImplementations 27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU14

27/04/08 rev 29/4/08CmpE 588 Spring 2008 EMU15 References  W3C Semantic Web Tools Wiki page.Semantic Web Tools  Jun Yuan, David H. Jones: Enabling Semantic Access to Enterprise RDB Data, Position Paper for W3C workshop on RDF Access to Relational Databases. Mathematics & Computing Technology, Boeing Phantom Works, P.O. Box 3707, M/C 7L-70, Seattle, Washington, 98124, U.S.A. Here. Jun YuanDavid H. JonesHere