Semantic Query Languages

1
Semantic Query Languages

• Atilla ELÇI
• Dept. of Computer Engineering
• Eastern Mediterranean University

2
What is Query Language?

• Webopedia A specialized language for requesting
  information from a database. For example, the
  query SELECT ALL WHERE age gt 30 AND name
  "Smith"
• 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.

3
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 users
  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!

4
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
• gt These non-semantic changes imply changes
  in queries therefore updates on IS relying on
  such queries. Yuan Jones

5
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

6
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

7
.QL

• An object-oriented query language used to
  retrieve data from relational database management
  systems. Wikipedia
• .QL language reference.
• A private initiative of Semmle Limited.

8
Library of Congress CQL

• CQL Contextual Query Language (SRU Version 1.2
  Specifications)
• Note its query syntax and some examples.
• Note its BNF definition.

9
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.

10
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
• 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 597-615.
• 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.

11
RDF Query Language

• A RDF query language is a computer language able
  to retrieve and manipulate data stored in
  Resource Description Framework format.
• 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.
• SPARQL is now a defacto standard.

12
W3C SPARQL

• SPARQL (pronounced "sparkle" 1) is an RDF query
  language. Wikipedia
• Its name is a recursive acronym that stands for
  SPARQL Protocol and RDF Query Language
• Standardized by W3C RDF Data Access Working
  Group.
• SPARQL 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.
• SPARQL Query Language for RDF
• W3C Recommendation 15 January 2008
• Defines the syntax and semantics of SPARQL query
  language for RDF.

13
SPARQL Query 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.
• Sect. 1 2 in W3C Recommendation 15 January 2008

14
SPARQL Software

• ESW Wiki Entry SparqlImplementations

15
References

• W3C Semantic Web Tools Wiki page.
• 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.