# RE: [UCR] RIF needs different reasoning methods

From: Gerd Wagner <wagnerg@tu-cottbus.de>
Date: Mon, 13 Mar 2006 10:33:38 +0100
To: "'Sandro Hawke'" <sandro@w3.org>
Cc: <public-rif-wg@w3.org>
Message-ID: <000201c64681\$360e7340\$55032b8d@TMGWAGNER>
```
> My understanding is that derivation rules and integrity
> constraints are
> just a bifurcation of Horn rules (or sometimes the two halves of
> something beyond Horn).  As such they fit easily into the same
> semantics.

Not really, there are both syntactic and semantic
differences:

- derivation rules, in general, correspond to Gentzen
sequents; in logics having a reasonable implication
connective (satisfying the deduction theorem), a
derivation rule may be viewed as an implication
formula; derivation rules are mainly used to express
definitions of derived predicates (or derived tables
in the style of virtual views); this means they are
applied at query time

- integrity constraints, in general, correspond to
sentences of some logic (which may be classical FOL,
temporal FOL or some modal FOL); as emphasized by
SBVR, they come with a modality (either alethic or
deontic) that determines their semantics in terms
of handling violations; integrity constraints are
used, at the business logic level, for expressing
all kinds of laws (includig structural and natural
laws); at the IT system level, they are mainly used
to catch all kinds of faulty states of the system
(such as referential integrity violations); this
means they are applied at state change time

Given all these differences, how can you say "they
fit easily into the same semantics"?

The fact that, in certain circumstances, they may both
take the form of a Horn formula does not mean they
have the same semantics (like a question Q and an
assertion A do not have the same semantics even if
Q and A are expressed with the same logical sentence).

-Gerd
```
Received on Monday, 13 March 2006 09:36:52 UTC

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