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RE: "If" and "else" in RDF

From: Danny Ayers <danny@panlanka.net>
Date: Sun, 29 Apr 2001 22:49:22 +0600
To: <www-rdf-interest@w3.org>
Message-ID: <EBEPLGMHCDOJJJPCFHEFIEDBDEAA.danny@panlanka.net>
I'm pretty sure there needn't be a contradiction, caused by
if...then...else, it's just how you actually express it - I'll try and find
the exact bit, but I think it's done in DAML+OIL using :  something is a
subclass of NOT something else

---
Danny Ayers
http://www.isacat.net

<- -----Original Message-----
<- From: Seth Russell [mailto:seth@robustai.net]
<- Sent: 29 April 2001 22:14
<- To: Murray Altheim; Danny Ayers
<- Cc: info@jan-winkler.de; www-rdf-interest@w3.org
<- Subject: Re: "If" and "else" in RDF
<-
<-
<- From: "Murray Altheim" <altheim@eng.sun.com>
<-
<- > You have guys have me really confused. Are you trying to find a way to
<- > express a material implication relationship, or perform a programmatic
<- > function? Turn RDF into a programming language? I don't get
<- it. Expressing
<- > relationships is one thing, actually acting on them is a whole
<- different
<- > bahoosus.
<-
<- Thanks, I think you have put you finger on the confusion.
<- Perhaps it was my
<- silly post which first started conflating the declarative description of
<- potential states of affairs with the actual acting on these
<- representations
<- by an agent to determine the actual state of affairs.
<-
<- From: "Danny Ayers" <danny@panlanka.net>
<-
<- > I think the confusion stems from the fact that 'if' and 'then'
<- (/'else')
<- are
<- > commonly used in both declarative and imperative computer languages. In
<- the
<- > declarative context if...then... goes right back to the basic
<- connectives
<- of
<- > propositional logic, where one can say if <something> then <something
<- > else> - a relationship is stated, there is no processing
<- involved. RDF is
<- a
<- > declarative language (a representation language, whether or
<- not you call
<- it
<- > a programming language is probably irrelevant), so surely this is the
<- > appropriate context here.
<-
<- I agree that the confusion is based on the fact that RDF is a declarative
<- language, whereas "if_then_action" is a programming language expressing
<- potential changes to states of affairs.   I believe the problem
<- stems from
<- the idea that a declarative language should always tell the
<- truth.  For the
<- RDF data model that amounts to saying that every labeled directed arc you
<- draw, must be deemed true in the model.  You are not supposed to state a
<- contradiction; but that is exactly what you need to do to declare a
<- "if_then_action".
<-
<- So getting back to Jan's question (and his most recent example
<- from an off
<- line discussion):
<-
<- From: "Jan Winkler" <jan_wi@jan-winkler.de>
<-
<- > if (mything:tax > '100$') then(mything:tax-type = 'not cheap')
<- > else (mything:tax-type = 'cheap')
<- > How should I do it without "if-then-else"? (to express a result or an
<- > inference)
<-
<- The problem is that to accurately represent that in a labeled
<- directed RDF
<- graph, you must  end up with a  statement that might look something like
<- this:
<-
<-         :Mything:tax  rdfs:label 'cheap' , 'not cheap'.
<-
<- which is plainly a contradiction.  In other words you are required to
<- declare potential facts which are in disjoint contexts .... and
<- the formal
<- logicians out there might object.
<-
<- I think this actually can be done with no contradiction ... but
<- we will need
<- to introduce some new concepts.  I have taken a stab at it in
<- the graph at
<- [1].
<-
<- [1] http://robustai.net/mentography/disjointDecision.gif
<-
<- Note that nodes that are black on white represent the things in
<- our domain
<- of discourse and static relationships between them.   The context nodes
<- (black on orange) allow us to state your "if-then-else"
<- restraint in a way
<- that is not contradictory.  However it is not meaningful unless
<- some active
<- process (black on red) actually computes the state of actual
<- affairs (black
<- on blue).
<-
<- Hopefully my silly detailed view of things does not add too much to the
<- confusion ....
<-
<- Seth
<-
<-
Received on Sunday, 29 April 2001 12:53:24 GMT

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