I received an offline question, which is of more general interest.
Therefore, I'm resending my reply to the whole forum, but deleting
any reference to the original sender.
___________________________________________________________________ (01)
The real problem of "bringing semantics" into anything, whether a
database or the WWW or anything else, is to keep your focus on the
main goal: representing meaning. Everything else is a distraction. (02)
> Is "semantic foreign key" possible to facilitate current relational
> database step into semantic database? In other words, if we can
> build RDF or OWL based semantic foreign keys across different tables
> and databases while providing those innovative foreign keys inference
> and reasoning ability, it may help to bring the semantics into the
> current DB. (03)
That is not the problem. People have been talking about integrating
semantics with relational databases for over 30 years. The solution
was always very clear: represent the meaning of the data in logic. (04)
The major obstacle was also very clear: people ignored meaning,
and devoted most of their efforts to adding more and more special
"features" to SQL to address one or another low-level syntactic
notation to support somebody's pet implementation. (05)
The major issues in creating the Semantic Web were also very clear:
express meaning in logic. But instead of focusing on the logic,
they started to address all kinds of special cases, such as using
triples instead of n-tuples or forcing everything into some kind
of XML syntax. (06)
If you step back and look at the logic, all the problems disappear: (07)
1. First order logic hasn't changed in the past 130 years, and
the syntax can be defined in half a page. (08)
2. The mapping of FOL to relational databases is obvious. (09)
3. The mapping of Description Logics to FOL is obvious. (010)
4. You can develop very clean, very simple mappings of the above
three to one another. (011)
5. The details of XML-based notations or table-based SQL notations
are of secondary importance. Those should *never* be allowed
to have the slightest influence on #1, #2, and #3 above. (012)
That is all very clean and very simple. But we still have to deal
with the problem of current systems such as SQL, RDF, and OWL. (013)
The answer is also simple: SQL, RDF, and OWL will be declared
"legacy systems". In the terminology that IBM used, they will be
called "functionally stabilized". That means no new features or
additions or further changes will be made to them. They will be
supported forever, but not as the basis for future development. (014)
All future development will focus on the very simple principles of
#1, #2, and #3 above and with further purely *logical* extensions,
not rinky-dink syntactic features of the kind that burden SQL,
RDF, OWL, and all other horrible syntaxes that have outlived
their usefulness. (015)
That is the answer. It's extremely simple, and it provides
*equal* support for both the current relational DBs and
the current Semantic Web. (016)
John Sowa (017)
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