Hi John,
Thanks for the change of subject line. I should have thought of that.
AW:
There should be a single clean programmer interface with well defined
semantics. The interface can be implemented with different subsystems,
but they should be completely hidden in a black box.
JS:
I very strongly agree. But you have to define the common semantics
first. Otherwise, the people who build the components will go off
in completely incompatible directions.
Actually, one can sometimes, inside the black box, code around previously implemented subsystems to get a clean semantics for a clean author-programmer user interface. For example, SQL from vendor A has different semantics from that of vendor B (Yes, really), but the black box can know this and act appropriately. Similarly, the black box can assign simple datalog semantics to RDF as in [1].
Not a beautiful approach, but it gets the job done.
Cheers, -- Adrian
[1] www.reengineeringllc.com/demo_agents/RDFQueryLangComparison1.agent
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
Adrian Walker
Reengineering
On Sat, Aug 11, 2012 at 11:07 AM, John F Sowa <sowa@xxxxxxxxxxx> wrote:
Adrian,
I basically agree with your comments, but I changed the subject line.
There is an important lesson about how the original vision for the SW
by Tim Berners-Lee faded into the pale shadow we see today.
AW
> As John has described, the result is a Rube Goldberg combination
> of different semantics of different components, reminiscent of the
> OWL/RDF/SPARQL "stack".
Actually, an SQL view is a very convenient and natural use of the
SQL WHERE clause. However, the SQL notation itself is rather kludgy.
I used to call SQL the world's worst notation for first-order logic.
But that was before I saw RDF and OWL. Since then, I have become
much more tolerant of SQL.
AW
> there should be a single clean programmer interface with well defined
> semantics. The interface can be implemented with different subsystems,
> but they should be completely hidden in a black box.
I very strongly agree. But you have to define the common semantics
first. Otherwise, the people who build the components will go off
in completely incompatible directions.
Recently, I read the DAML proposal from 2000 by Tim Berners-Lee.
It presented a vision for the Semantic Web that is far superior
to anything that has happened to it in the past 12 years:
http://www.w3.org/2000/01/sw/DevelopmentProposal
Tim B-L:
> The proposed project is to utilize and demonstrate the great power of adding,
> on top of the RDF model (modified as necessary) the power of KR systems.
> We refer to this augmented language as the Semantic Web Logic Language, or SWeLL.
> We propose to build on the DARPA Agent Markup Language (DAML) infrastructure
> to provide precisely such an interchange between two or more rather different
> kinds of applications.
I urge everybody to read that document. It SWeLL shows as a combination
of propositional logic, first-order logic, and higher-order logic. It is
also intended to support extensions to nonclassical logic. That sounds
very similar to Common Logic. Pat Hayes was working on the logical
foundations for both CL and RDF during the early days.
Two important terms in that report are 'heterogeneous', which occurs
6 times, and 'interoperable', which occurs 12 times in variations such
as 'interoperating' and 'interoperability'. Among other things, DAML
is intended to support both RDF databases and relational DBs. Near the
end of Section E: "The diversity of systems successfully interfaced
to the Semantic Web will be an important indicator of success."
I also did some searching for subsequent DAML reports, which show a
progressive narrowing of that vision. A year later, Tim still talks
about "RDF/DAML/SWeLL messages" and "SWeLL rules". And he mentions
"the DAML Ontology Language (DAML+OIL)". Today, people talk about
OWL as "a combination of DAML and OIL", but the early reports show
that DAML+OIL was just one component of a much richer system:
http://www.w3.org/2002/02/iow2
The early documents on DAML+OIL specify the axioms for OIL in terms
of KIF, which was also the starting point for Common Logic. But
the next report shows an ominous development:
http://www.w3.org/2002/11/DAML-IOW
Tim B-L:
> We are specifying a framework, the Semantic Web Logic Language (SWeLL),
> on top of RDF, DAML+OIL, and OWL in which a variety of logic system can
> be expressed for interchange between applications.
You cannot paste a common semantics "on top of" other components.
The semantics *must be* the foundation. Instead of specifying OWL
in terms of KIF (or SWeLL), they specified an independent model
theory for OWL. That was the beginning of the end. The hope
of a unifying semantic foundation was dying.
For more citations and commentary about these developments, see
http://xml.coverpages.org/daml.html
The letter A in DAML is for Agent, but the idea of multiple agents
interoperating in heterogeneous systems is lost in later reports.
I was enthusiastic about the Semantic Web at the beginning, but
the original vision has vanished.
John
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