Re: [ontolog-forum] Lightweight, middleweight, and heavyweight semantic

[Adrian Walker <adriandwalker@xxxxxxxxx>]

Hi John,

There's a related way of zooming in on three kinds of semantics, and it can be argued that there are many advantages in ensuring that they work seamlessly together in one software system:

Semantics 1:  data semantics , as in the interleaving of metadata with data in RDF, or a schema-data pair in SQL.

Semantics 2:  specifies what conclusions a reasoning engine should in principle be able to infer from any set of clauses (typically a model- or fixpoint-theory).

Semantics 3:  concerns the meaning of English concepts at the author- and user-interface.

The paper [1] argues that integrating these semantic dimensions in one system has the potential not only to support aspects of the Semantic Web, but also to ease some significant problems in commercial IT.  The paper also describes a live system on the web [2] that implements these ideas.

Unfortunately, current semantic web languages are in a state of high semantic confusion (particularly in respect of Semantics 2), see e.g. today's posting [3]  from Antoine Zimmermann.  

What do you see as the future trends among the semantic web languages?  

                                  -- Adrian

[1] www.reengineeringllc.com/A_Wiki_for_Business_Rules_in_Open_Vocabulary_Executable_English.pdf


[2]  Internet Business Logic
A Wiki and SOA Endpoint for Executable Open Vocabulary English Q/A over SQL and RDF
Online at www.reengineeringllc.com    
Shared use is free, and there are no advertisements

[3]  <quote> 
Now I'd like to show some of the strange things that happen when you combine SPARQL with inference regimes, that are due to the inability to have literals (in the syntax) as subject.

Assume that you have the following data, harvested from the Web:

:www dc:creator "Tim Berners-Lee" .
:www dc:creator "Tim Berners-Lee"^^xsd:string .
:www dc:creator :timbl .
:timbl owl:sameAs "Tim Berners-Lee" .


Note that literals are commonly used with dc:creator so this example is fairly realistic.

Now, let us consider the following query:

SELECT ?x WHERE {
  ?x a rdfs:Resource .
}

under the RDFS-entailment regime, this would provide the following answer:
?x --> :timbl

Now, the following query:

SELECT ?y WHERE {
  ?y a rdfs:Literal .
}

would provide no answer (under RDFS-entailment) and:

SELECT ?z WHERE {
  ?z a xsd:string .
}

would provide no answer (under RDFS-entailment).

Now, imagine a SPARQL engine with an "RDFS+sameAs"-entailment regime. The three queries above would give the following results:

?x --> :timbl   // first query
?y --> :timbl   // second query (I can infer that :timbl is a rdfs:Literal)
and the last would give nothing.

Now consider the query:

SELECT ?t WHERE {
   ?u a rdfs:Literal .
   ?u owl:sameAs ?t .
}

It would give:

?t --> "Tim Berners-Lee"
?t --> :timbl

However, the query:

SELECT ?u WHERE {
   ?u a rdfs:Literal .
   ?u owl:sameAs ?t .
}

would give ?u -> :timbl .


This is very weird for me.</quote>

   --  antoine.zimmermann@xxxxxxxx    20100701

On Fri, Jul 2, 2010 at 10:20 AM, John F. Sowa <sowa@xxxxxxxxxxx> wrote:

After the SemTech conference and some further discussions on related
topics, I realized that many of the debates about the kinds of logics
and ontologies could be clarified with some useful distinctions.
Different kinds of applications require different levels of detail
and precision in the definitions and different levels of expressive
power in the logic.

To make the distinctions memorable, good labels are necessary.
I suggest the following four levels of semantics:

 0. Zero semantics:  Data with no explicit semantics of any kind.

 1. Lightweight semantics:  Some semantic tagging with terminologies
    or folksonomies, loose hierarchies such as WordNet, but no formal
    definitions, logic, or reasoning methods.

 2. Middleweight semantics:  Some formal notations, but only a modest
    amount of logic and reasoning.

 3. Heavyweight semantics:  Detailed ontologies represented in a
    rich version of logic with extensive reasoning.

There are gradations of levels from Comma Separated Values to Cyc,
The Linked Data applications are at levels 0 and 1.  They usually
depend on traditional terminologies and folksonomies that have
no formal definitions.

Most Semantic Web applications are at levels 1 and 2.  RDFS and
RDFa use tags that don't have detailed definitions.  Light use
of OWL supports middleweight semantics, but extensive use of
all the OWL features begins to cross the boundary between
middleweight and heavyweight semantics.

Software specifications typically use informal, lightweight
semantics in requirements documents.  The UML diagrams for type
hierarchies and Entity-Relationship diagrams support lightweight
semantics.  More detailed diagrams support middleweight semantics.

But a precise specification of any computer program and the data
it processes requires heavyweight semantics.  Most specifications
aren't that precise, but such precision is necessary if two or more
independently developed programs are intended to be compatible
(for example, two compilers for the same programming language).

Many systems require a mixture of levels.  For example, the data
shared by multiple applications may be tagged by semantic markers
at level 1, but the internals of the applications would require
heavyweight semantics to specify the details of the computation.

As another example, Cyc has been used for medical informatics.
The source data may include a mixture of levels 0, 1, and 2,
but the full Cyc system uses heavyweight semantics to analyze,
relate, and interpret the data.

Many of the debates we've had in this forum result from
different people focusing on different kinds of applications
that use different levels of semantics.  The issues would be
easier to resolve if we keep track of the different levels.

John Sowa

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