Bell Labs

RDF: Back to the Graph

Peter F. Patel-Schneider
Bell Labs Research
Alcatel-Lucent

26 June 2010, RDF Giant Steps Workshop

Copyright © 2010 Bell Labs

A suggestion to move RDF back to a data-structuring language, plus musical accompaniment (with apologies to Monty Python).

Bell Labs

What is RDF?


  1. Data structuring language
    • Triples, Nodes, and Edges
    • The RDF Graph
  2. Knowledge representation formalism
    • RDF Semantics

There are DB designers in the world.
There are OO programmers.
There are Lispers and even logicians, and then
There are those that use ML, but
You've never been any of them.

You're true blue RDFers,
And have been since before you were born,
And the one thing that's said about RDFers is:
They'll take implementors as soon as they're warm.

You don't have to be a six-footer.
You don't have to have a great brain.
You don't have to have any math knowledge. You're
An RDFer the moment Tim came,

Because

Every triple is sacred.
Every triple is great.
If a triple is wasted,
Tim gets quite irate.

Bell Labs

What's Wrong with That?


Nothing, except if RDF is the basis of the Semantic Web in same-syntax semantic extensions, where:

  1. all syntax is (all) triples; and
  2. all semantics builds on RDF semantics.

Same-syntax semantic extensions result in paradoxes (or incomplete, strange logics) because the syntax of the logic ends up in the semantic domain of the logic.

RDF COMMUNITY:
Every triple is sacred.
Every triple is great.
If a triple is wasted,
Tim gets quite irate.

RDF PROMOTER:
Let the others spill triples
On academic ground.
Tim shall make them pay for
Each triple that can't be found.

W3C TEAM MEMBER:
Every triple is beautiful
W3C TEAM MEMBERS:
Every triple is wed
W3C TEAM MEMBER:
To its eternal meaning
W3C TAG:
In the Semantic Web.

Bell Labs

Current Status


RDF as this complete basis is already breaking down.

  • Different syntaxes for OWL
  • Different semantics for OWL
  • RIF syntax
  • SPARQL syntax
  • Incomplete RDF(S) implementations

FOAF IMPLEMENTORS:
Every triple is correct.
Every triple is bright.
FOAF USERS:
Tim will let no triple
ALL FOAF:
Away from his oversight.

Bell Labs

Changing the Game


Let's remove both parts of this vision of the Semantic Web!

  • Semantic Web semantics is not an extension of the RDF semantics.

W3C TEAM MEMBER:
Every triple is beautiful
W3C TEAM MEMBERS:
Every triple is wed
W3C TEAM MEMBER:
To its eternal meaning
W3C TAG:
In the Semantic Web.

  • Semantic Web syntax is not just triples.

W3C COMMUNICATIONS HEAD:
Let the unbelievers produce syntax
For languages complex or plain.
W3C PUBLICATION TEAM:
Tim shall strike them down for
Each triple that's wasted in vain.

Bell Labs

Who Else Plays this Game


This is how extensions in other descriptive families are done

  • propositional logic
  • first-order logic
  • higher-order logic
  • intensional / temporal logic

Each extension has additional syntax and most modify old syntax. Most also modify the semantics (but in a way that maintains compatablity).

W3C FELLOW:
DLs, logic, OOP,
Spill syntax just anywhere,
Tim loves only RDF, which treats its
Syntax with more care.

Bell Labs

The Result


Going all out this way would result in:

  • RDFS having its own syntax;
  • OWL having its own syntax;
  • RIF having its own syntax;
  • SPARQL having its own syntax;
  • but all having (mostly) compatible semantics.

Gee this is beginining to sound familiar!

RDF COMMUNITY:
Every triple is useful.
Every triple is fine.
STARTUP'S EMPLOYEES:
RDF needs everybody's.
IMPLEMENTOR #1:
Mine!
IMPLEMENTOR #2:
... And mine!
USER:
...... And mine!

Bell Labs

Getting RDF Back


Can we put RDF back in the center?

  • Sort of, provided that RDF is just data.
  • RDF retains its other aspects.
    • Any graph is acceptable.
    • IRIs, ....
  • Freedom from blinding triples,
    where all triples carry truth.
  • Higher languages can use RDF as a neutral data-structuring language.
  • RDF still supports linked data.

RDF COMMUNITY:
Every triple is wanted.
Every triple is good.
Every triple bears truth
In a graph's neighbourhood.

Bell Labs

Whither then RDF?


RDF could be used directly as a data-structuring language or it could be used as (part of) the syntax of a representation language (RL).

  • The RL could cut down acceptable inputs.
    • Bad typed literals are syntax errors.
    • Restrict use of some vocabulary.
  • The RL could also augment RDF with another syntax, e.g.,
    • RDF for property values and types, other syntax for ontologies.

PETER:
Triples are good for data
But not also for syntax or truth.
Free the Web from tyranny
By triples bearing syntax and truth.

Every triple will be data.
Every triple will be free
In the Semantic Web
To achieve its destiny.

Bell Labs

What does this Change?


  • Not much, per se, as much of it is already in place.
  • Linked data appears to work this way already.
  • But the future is much freer:
    • RDF can expanded beyond triples to
      • quads, n-tuples, lists, trees, ...;
      • explicit provenance, certainty;
      • named graphs;
      without affecting RDFS or OWL.
    • RLs could project out, e.g., provenance, to get back triples.
    • AWLful could go away.

PETER:
Triples, quads, and lists,
They all seem good to me.
Allow any data structure
Even an n-ary tree.

For

Every structure is useful.
Every structure is fine.
We need every structure,
Yours, and theirs, and mine.

Bell Labs

Living with the Past


How to make this all work out while old-style RDF remains?

  • Add new MIME types for
    • RDF as data,
    • RDF encoding RDFS,
    • RDF encoding OWL, and
    • OWL ontology in XML.
  • Retain existing RDF MIME type for uncategorized RDF.

ALL RDF LOVERS:
Every triple is correct.
Every triple is bright.
Tim will let no triple
Away from his oversight.

Every triple is wanted.
Every triple is good.
Every triple bears truth
In a graph's neighbourhood.

Every triple is beautiful
Every triple is wed
To its eternal meaning
In the Semantic Web.

Every triple is sacred.
Every triple is great.
If a triple is wasted,
Tim gets quite iraaaaaate!

Bell Labs

The New RDF Order