Re: current draft of SWSL Rules design doc

From: Sandro Hawke (sandro@w3.org)
Date: 07/27/04

  • Next message: Benjamin Grosof: "overview slides on SWSL Rules" 
    >    a. Constants
> 
>        A constant is either a literal or a URI.
...
>        URI:
>          - a complete URI (protocol://location...)
> 	   - a Qname (prefix:...)
> 
> 	 Both must conform to the W3 specs.

The "//" is only present in some situations, so you cannot rely on it
to syntactically distinguish between URIs and QNames.  (For example,
"mailto:bgrosof@mit.edu" is a URI.)  Technically, QNames conform to
the URI syntax; they are not disjoint.  In practice, almost every URI
in use violates the QName syntaxs (eg with the "@" in mailto), so you
could carve out the QName part of the URI syntax, but that's still
kind of risky.

I don't have a great alternative.   N3 uses angle-brackets around URIs
and nothing around QNames.   SWI Prolog has URIs be atoms (surrounded
by single-quotes, in normal prolog syntax) and QNames be terms with a
":" infix operator (which are usually rewritten at parse-time).

      -- sandro

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