RQL Querying the Presentation Layer

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RQLQuerying the Presentation Layer
On-To-Knowledge review deliverable 9

• Jeen Broekstra
• jeen.broekstra_at_aidministrator.nl
• Arjohn Kampman
• arjohn.kampman_at_aidministrator.nl

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Goal of this presentation

• Presenting a brief history of RQL and
  aidministrators role in its development.
• Explaining design choices in the On-To-Knowledge
  version of RQL.

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Contents

• Place in the project
• RDF and RDF Schema
• Why RQL in On-To-Knowledge?
• More on RQL
• Origin
• Design and capabilities
• OTK-RQL
• Some example queries
• Conclusions future work

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RDF

• Statements about resources
• Triples (subject, predicate, object)
• Chaining graph model

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RDF Schema

• Defines vocabulary for RDF
• Organizes this vocabulary in a typed hierarchy
• Class, subClassOf, type
• Property, subPropertyOf
• domain, range

Person
subClassOf
subClassOf
range
domain
Student
Researcher
hasSuperVisor
type
type
hasSuperVisor
Jeen
Frank
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Why RQL in On-To-Knowledge?

• Language for the representation layer is
  DAMLOIL, an extension of RDF Schema.
• RQL the only good candidate query language
• Only one to support RDF Schema semantics.
• Very well-defined semantics and very expressive
  querying capabilities.

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RQL Origin

• ICS Institute of Computer Science
• FORTH Foundation for Research and Technology
  Hellas
• RQL developed in a 1-year IST feasibility study
• C-Web a Generic Platform supporting
  Community-Webs
• Further development planned in follow-up European
  project MESMUSES.
• RDFSuite a complete set of tools for storing and
  querying RDF.

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RQL Design

• Based on OQL (standard QL for Object-Relational
  DBMS)
• Set of core queries
• Class, Property, subClassOf,
• filters
• select-from-where
• Boolean expressions
• Functional composition of queries
• Path expressions
• XauthorY.mentionedByZ
• For navigating the RDF model
• Allowing bridging between RDF data and schema
  information
• Tailored to the RDF Graph Model
• Fully aware of RDF Schema semantics

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OTK-RQL

• Enhancements to original RQL
• Better compliance to W3C standards
• RDF Schema semantics are at some points ambiguous
• Different user requirements in OTK vs. MESMUSE
  make different interpretations desirable.
• Convergence on these differences should be
  reached at a later stage.
• Implementation by aidministrator Sesame
• Server-based
• DBMS-independent

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Some example queries

• Basic queries
• Return all classesClass
• Return all instances of ResearchPaperhttp//w
  ww.enersearch.se/ontoResearchPaper
• Return all subclasses of ResearchPapersubClas
  sOf(ResearchPaper)
• Return all propertiesProperty

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Example queries (2)

• More advanced
• Return all authors whose last name starts with
  P or with an Rselect AUTHORfrom Author
  AUTHOR. lastName LNAMEwhere LNAME like
  P or LNAME like R
• Return the properties a ResearchPaper can have,
  and their domain and rangeselect _at_P,
  domain(_at_P), range(_at_P)from X _at_Pwhere X
  ResearchPaper

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Conclusions

• RQL is powerful and flexible.
• OTK-RQL is an enhancement of RQL that is more
  compliant with W3C.
• Future plans
• Convergence of the two RQL versions.
• Implement Query Engine (already in progress)
• Bring RQL into the W3C as a proposed standard.
• Investigate extension to DAMLOIL QL.