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Re: ISSUE-76: Equality in Core? [Core]

From: Dave Reynolds <der@hplb.hpl.hp.com>
Date: Sun, 14 Sep 2008 20:59:07 +0100
Message-ID: <48CD6D0B.6000902@hplb.hpl.hp.com>
To: Rule Interchange Format Working Group WG <public-rif-wg@w3.org>

This issue was discussed at the last telecon with only myself expressing 
any reservations. The chairs expressed a desire to either resolve this 
or at least draft a resolution at the next telecon. Since I won't make 
that telecon I'm putting my position in email.

Summary: I'll withdraw my concerns and accept unrestricted equality in 
rule bodies in Core.

Comments:
There was some discussion on Tuesday about this being purely identity or 
syntactic quality.  That's not true in the presence of data types as 
Michael later pointed out.

I expressed a preference that this should be handled via a generalized 
equality builtin rather than a syntactic construct. The primary reason 
being to allow us to use any binding pattern machinery we might devise 
(to express safety or conformance restrictions) to equality as well. I 
realize that there is not yet any acceptable proposal for binding 
patterns so this is a theoretical reservation and I'll accept that it's 
not strong enough to justify deviation from BLD/PRD.

Dave

Rule Interchange Format Working Group Issue Tracker wrote:
> 
> ISSUE-76: Equality in Core? [Core]
> 
> http://www.w3.org/2005/rules/wg/track/issues/76
> 
> Raised by: Jos de Bruijn
> On product: Core
> 
> There is already a widespread consensus that Core will not allow equality in the rule heads.
> 
> The question which remains: Will Core allow equality in the rule bodies?
> It is known that introducing equality in rule bodies does not increase expressiveness: rules with equality in the body can be straightforwardly equivalently (i.e., they have the same models) rewritten to rules without equality.  So, equality in the body is simply a syntactic shortcut.
> 
> It is argued in [1] that a restricted form of equality should be allowed in the rule bodies to facilitate external function calls.  However, as mentioned above, this equality is not necessary.  It is simply a syntactic shortcut.
> 
> 
> So, we basically have three choices:
> a) allow equality in rule bodies
> b) allow only a restricted form of equality in rule bodies, as argued in [1]
> c) not allow equality in rule bodies
> 
> 
> To me personally, (b) does not make sense.  Why allow equation of variables and functions, but not variables and variables?
> So, I argue that we should either (a) allow or (b) disallow equality in rule bodies.
> 
> 
> 
Received on Sunday, 14 September 2008 19:59:53 GMT

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