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

From: Benjamin Grosof (
Date: 11/04/03

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    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.
    An atom here could be a variable-ized OWL-DL complex class expression, in 
    the extension to permit those.
    >       -- 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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