Peter, Kingsley, Doug, and Ed, (01)
Before commenting on your comments, I'd like to remind everyone that
what is now called the Semantic Web represents just a small subset of
the vision that Tim Berners-Lee presented in his proposal of Feb 2000. (02)
In that proposal, Tim explicitly addressed the issues that Ed raises.
He didn't present a complete solution, but he summarized the issues,
and he outlined the directions that needed further development. See
the excerpt the end of this note. (03)
PY
> I would like to point out that your statement, "The major goal
> of Ontolog Forum is to develop logic-based methods for representing
> and using formal ontologies," represents only part of the ONTOLOG
> mission... (04)
Yes. I admit that it is much too short to cover everything. My only
excuse is that I was trying to be brief. (05)
KI
> The problem always boils down to webby data object representation,
> access, and relationship semantics that scales to the Web. (06)
Unfortunately, I must agree with Ed B and with Tim B-L that it is
impossible to have consistent semantics that scales to the size
of the WWW. Tim implied that in the excerpt copied below, but his
recommendations for addressing the problem were ignored. (07)
KI
> we reached the point of critical mass a long time ago (08)
DF
> Until you know the context of specific data ("electricity") supply,
> you combine two supply streams at your own risk. (09)
Yes. When you have billions of inconsistent triples, efficiency
is not the problem. Without doing a single inference step, we can
state with complete confidence that they imply (p & ~p). From that
contradiction you can derive any conclusion you wish. (010)
KI
> Facebook has a Billion profiles and much more from its data space alone (011)
EB
> And a great many utterly uninformed and uninformative postings, to say
> nothing of baseless attacks and deliberate frauds. The question is:
> what portion of that cacophony is signal? And how would you know? (012)
Tim recognized that problem. His vision of the SW was a collection
of *heterogeneous* systems, not billions of triples that could be
processed by a single homogeneous algorithm. (013)
From the last paragraph below:
> The Semantic Web works by allowing each individual system to maintain
> its own language and characteristics. The access control system works
> with finite sets of people, groups, and documents, and allows constrained
> expressions for access control. (014)
In Tim's vision, the SW is a collection of *finite* systems, each with
its own language and with its own access controls. Different systems
may share data, but each one is responsible for maintaining access
controls that limit unconstrained inferences across billions of triples
from unconstrained sources. (015)
Tim's full proposal is important, but the following section is critical
for understanding what has to be done to address the issues Ed raised.
Unfortunately, the current SW tools ignore these issues completely. (016)
John
______________________________________________________________________ (017)
Source: http://www.w3.org/2000/01/sw/DevelopmentProposal (018)
Logic of Authority (019)
In practice -- in a distributed decentralized world -- some sources will
be more reliable (on some topics) than others and different sources may
even assert mutually contradictory information. RDF is based on XML for
which digital signature standards are expected to emerge early in the
life of this project. XML Digital Signature will be used to provide an
authentication component in this project. SWeLL
(Semantic Web Logic Language) processors will generally be aware of the
source and authority for each piece of information. Information will be
processed differently as a function of trust in its source. (020)
It is not enough for facts to be shared between different data systems,
or even for signed data to be shared. Several logic-based languages have
been used with some success as knowledge interchange languages (e.g.
SHOE, KIF, etc.). In these systems RDF-like facts are augmented with
rules that combine logical information with directives for effecting
inference. Such directives are not always exchangeable between different
types of KR systems, but the logical relationships must be expressible
in SWeLL. For this, SWeLL extends RDF by including negation and explicit
quantification. (021)
But to achieve its full potential, the Semantic Web must do more. The
Semantic Web is composed of heterogeneous systems. No real system can
answer every possible question about its data (i.e. none can compute the
deductive closure of its information). Different systems make different
compromises, affording different sets of inferences. For this reason,
one application will often be able to reach a particular conclusion when
another does not. (022)
In the general case, one piece of software will need to be able to
explain or justify to another why its assertions ought to be accepted.
This allows an untrusted system to effectively communicate information,
by compellingly justifying that information. The steps of such a
justification amount to a logical proof of the assertion, and the final
key element of the Semantic Web is a proof verification system that
allows justifications and inferences to be exchanged along with raw data. (023)
Thus, a heuristic of one system may posit a relationship (such as that a
person may access a web page) and succeed in finding a logical
justification for it. This can be conveyed to a very rigid security
system that could never have derived this relationship or its
justification on its own, but which can verify that the justification is
sound. (024)
The Semantic Web works by allowing each individual system to maintain
its own language and characteristics. The access control system works
with finite sets of people, groups, and documents, and allows
constrained expressions for access control. (025)
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