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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.

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.


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 UTC

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