Re: [PRD] class membership assertions

Hi Jos,

Jos wrote on 12/05/2010 11:01:05:
> 
> I found a strange discrepancy in PRD. In the definition of assert 
> fact actions [1], it is possible to assert class membership facts.
> Now, I understand that there is a shortcut syntax for asserts in the
> XML [2] and presentation [3] syntaxes. In particular, it's not 
> necessary to write the "Assert" for positional and frame atoms. 
> However, if one wants to assert a class membership formula, one is 
> required to write the "Assert".
> Why is there this discrepancy? Was that an oversight?

The reason is that the "Assert-free" syntax is the recommended syntax for 
PRD rules that are also Core.

But the assertion of a class membership is allowed, in PRD, only for newly 
created instances, that is, inside a Do, and after an action variable has 
been bound using the New construct [1]: in other words, a PRD rule that 
asserts a class membership cannot be Core, and the "Assert-free" syntax 
would not make sense in that case (even for positional atoms and frames, 
the "Assert-free" syntax is not allowed inside a Do).

[1]http://www.w3.org/TR/rif-prd/#def-wf-action-block

Cheers,

Christian

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