• From: Dan Brickley <danbri@d...>
• To: "Costello, Roger L." <costello@m...>
• Date: Sun, 01 Mar 2009 15:32:32 +0100

On 1/3/09 14:03, Costello, Roger L. wrote:
> 1. If something is in the realm of "semantics" does that mean it can only be processed by humans (eyeballs)? It cannot be processed by machines?
[...]
> WHAT IS SEMANTICS?
>
> Something is semantics if it cannot be simply specified in a declarative manner or it requires procedural code to express it.

Some aspects of meaning can be made quite readily machine-checkable.

If you say something is a Person, and if you use vocabulary in which 
Person and Document are disjoint classes, don't in the same breath 
ascribe properties to that thing which imply it is a Document. Machines 
can spot when you do this, even with simple RDFS+OWL schemas like FOAF. 
They can figure out, "hey, no true description of the world could ever 
fit this picture, what's up?".

If you are working with RDF (RDFS/OWL) content, and the only rules you 
have are RDFS schemas and OWL ontologies, then you're pretty much 
limited to this kind of checking. However there are many more ways of 
screwing up in data, whether or not in RDF(expressing falsehoods, being 
incoherent or unintelligible or boring or vague), beyond contradicting 
yourself. For RDF, we can build machine-friendly checkers for some of 
this directly top of the RDF/OWL layer either directly in a query 
language (eg. SPARQL) or indirectly by generating the SPARQL from OWL 
plus some unwritten assumptions.

Some trails back to 2001 here... and Schematron-inspired RDF work on 
expressing integrity constraints:

http://www.xml.com/pub/a/2001/02/07/schemarama.html
http://ilrt.org/discovery/2001/02/schemarama/
http://isegserv.itd.rl.ac.uk/schemarama/
http://danbri.org/words/2005/07/30/114
also
  http://clarkparsia.com/weblog/2009/02/11/integrity-constraints-for-owl/
  http://jena.sourceforge.net/Eyeball/

Note than in RDFland, folk sometimes talk about its graph data model as 
a kind of abstract 'syntax'. Especially OWL people lately. I don't 
expect terminologies here to ever fully converge, too many compsci, 
engineering and other traditions are jumbled up together when they meet 
Web standards.

cheers,

Dan

--
http://danbri.org/

• Follow-Ups:
  • RE: Syntax versus Semantics (was:"vocabulary constraints" and other constraints
    • From: "Cox, Bruce" <Bruce.Cox@U...>

• References:
  • Syntax versus Semantics (was: "vocabulary constraints" and otherconstraints (was: Re: RE: Difference between "normalize" and"canonicalize"?))
    • From: "Costello, Roger L." <costello@m...>