Re: technical detail feedback on OWL Rules: truth value for empty consequent

From: Ian Horrocks (
Date: 11/05/03

  • Next message: Sandro Hawke: "Rules WG -- draft charter -- discussion on www-rdf-rules"
    On November 4, Benjamin Grosof writes:
    > At 07:19 PM 11/4/2003 -0500, Sandro Hawke wrote:
    > > > Remove the condition that a consequent is a conjunction. Its never a
    > > > conjunction, except as syntactic sugar for a conjunction of rules
    > > > each with a singleton-disjunction consequent.
    > >
    > >It needs to be a conjunction to get Horn expressivity using
    > >existentials scoped inside the consequent, right?
    > no that's not really the issue, it's much simpler -- just a choice of the 
    > syntactic convention for conjunction of atoms in the head.
    > We mainly need to define the truth value of an empty head as false rather 
    > than true.  The simplest way to define that would
    > be to permit the head only to be either a single atom or empty, as Pat 
    > suggests.  Or one could more permissively define it to be: a conjunction of 
    > one or more atoms, or empty (interpreted as false), which is basically what 
    > the mid-Oct. draft intended.
    To reiterate, the mid-Oct draft didn't "intend" this, it stated it
    Of course we may want to change the presentation to do a better job of
    explaining why the current semantics say what they say (or we may even
    want to change the semantics).
    > An atom here could be a variable-ized OWL-DL complex class expression, in 
    > the extension to permit those.
    >   B
    > >       -- sandro
    > ________________________________________________________________________________________________
    > Prof. Benjamin Grosof
    > Web Technologies for E-Commerce, Business Policies, E-Contracting, Rules, 
    > XML, Agents, Semantic Web Services
    > MIT Sloan School of Management, Information Technology group
    > or

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