Re: [TED] An alternative proposal for the technical design

Dave Reynolds wrote:
> 
> Could you clarify what are the essential ways your proposal differs from 
> the current one, as separate from accidental differences of expression?

As everybody noticed, the main point is not the syntax (although my 
proposal may require a more general syntax).

> For the expression component (setting aside rules for the moment) is 
> there an intended difference in semantics? Your words suggest an 
> underlying two-valued logic. Michael's semantics seems to be designed to 
> permit logics with 3, 4 or more truth values. Is this an essential and 
> intended difference?

No. I see no reason not to agree with Michael's semantics wrt admitting 
logics with n truth values.

My main point is that, from the point of view of RIF, the intended 
meaning of an atomic expression is given from the outside (and, thus, 
that their semantics is out of scope for RIF). RIF has to specify the 
semantics of the allowable combinations of atomic expressions, basically 
the modifications of atomic expressions (such as negation) and their 
conjunction and disjunction. I propose that we include the ones on which 
everybody agree (e.g. conjunction and disjunction) and that we leave the 
ones on which there may be discussions for phase 2.

Same with n-valued logics: if everybody agrees on the semantics of these 
operators for n truth values, why not include it in RIF? I have no 
problem with Michael's semantics in this respect, but I am not really 
competent.

 From a syntax point of view, the only other thing I saw that RIF should 
specify regards the variable bindings (hence the quantification 
expression, on the semantics of which I do not think there is any 
disagreement). But I may be wrong: I do not claim to be complete.

> Then looking at the words on rule semantics I struggle to understand 
> whether you are saying "no semantics for rules, let individual parties 
> decide" or whether you are saying "procedural semantics, iterate to 
> fixed point". Your Rule examples and Ruleset discussion seem to be 
> pulling in different directions.
> 
> I think there's an interesting proposal somewhere in here but a sharper 
> expression of the primary things you are trying to do, separate from the 
> philosophy, would help.

I fear that you are asking for the impossible, since what I am trying to 
do is to propose a different philosophy for RIF :-)

My main point is that people are interchanging rules for a purpose, and 
that the current design does not take that fact into account. I tried to 
think of another approach where that fact could be leveraged to make RIF 
simpler; and usable, where relevant, to interchange rules even between 
rule languages with different semantics (another concern I have with the 
current approach: it does little if anything for interoperability).

Let me try another way: assumed there are rules that can be equivalently 
expressed in all different kinds of rule languages, for all practical 
purposes, at least, even though these rule languages do not share a 
common semantics. Now:
1. If the same rule/ruleset can be expressed in different languages, it 
means that they can be interchanged between these languages in a way 
that preserves their meaning;
2. If they can be expressed in languages that do not share a common 
semantics, it means that the "semantics" of the rules can be abstracted, 
for the purpose of interchange, from the specific semantics used by the 
various rule languages for the purpose of reasoning/inference.

My proposal is that RIF could be designed as a general (and extensible) 
syntax for interchanging rules, where the CORE would only have that 
minimal "abstract semantics" that enable the interchange of those rules 
where that "abstract semantics" is enough to preserve the meaning.

That is where the fact that people interchange rules for a purpose is 
important: I propose to leave it to those people to decide wether that 
minimal semantics is enough for their purpose or not, and so, whether 
they can use the core or whether they need a more "powerful" version of RIF.

I propose that the "abstract semantics" for a single rule could be: if 
the antecedent holds (whatever we agreed it to mean), then, the rule 
means that the consequent would be expected to hold too (whatever you 
choose to do with that expectation is your problem). Same level of 
abstraction for a ruleset.

Extensions would then be specified to handle the cases where a more 
specific semantics is required (and, here, it is not a problem that the 
rules can be interchanegd only among the rule languages based on that 
specific semantics).

I wonder if what I propose is not akin to what Jim Hendler discusses in 
the first section of an email he sent during the discussion about the 
charter (mutatis mutandi):
http://lists.w3.org/Archives/Public/public-rule-workshop-discuss/2005Aug/0080.html

Christian

Received on Tuesday, 31 October 2006 15:35:23 UTC