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Re: [PRD] review of the frozen draft of Nov 25

From: Christian de Sainte Marie <csma@ilog.fr>
Date: Tue, 02 Dec 2008 14:45:54 +0100
Message-ID: <49353C12.1030909@ilog.fr>
To: kifer@cs.sunysb.edu
CC: RIF WG Public list <public-rif-wg@w3.org>

Michael,

Thanx for the very detailed review. Here below some first replies.

Michael Kifer wrote:
> 
>       Editorial comments
> 
>     * The nesting level of sections is 4 - too deep compared to BLD,
>       which has only a few level-3 sections. I suggest to get rid of
>       "Abstract Syntax & Semantics" and make "Conditions", "Actions",
>       and "Production Rules" into top level sections 2, 3, and 4,
>       respectively.

Is the nesting level really problematic? The point is that, if we get rid of the "Abstract syntax and semantics" and "XML syntax" level, we the "Condition", "Actions" and "Production rules" sections repeated twice.

Or would it be ok to keep 4 levels in te "XML syntax" section?

>     * It would be very helpful to put the square sign ☐, character
>       #9744, at the end of every definition and example.

Right. But I do not know how :-) (ok, found it. We will add them)
 
>     [references]

Right. References need be checked and repaired.

>     Specific Comments
> 
>    1. Sec 1, above Ex 1.1: /Actions can modify the facts, not only the
>       knowledgebase/
> 
>       Usually facts are considered part of the knowledge base, so this
>       remark can be confusing to some readers.

I rewrote that: "Actions can modify the facts themselves, not only extend the knowledge." Is that any clearer?

>    2. Same page: /2. Conflict resolution/.
> 
>       Would be appropriate to briefly explain this notion here.

Is it the reference to a strategy that is unclear, in the short explanation ("select rule instances to be executed, per strategy")? Would "apply predefined selection strategy to select rule instances to be executed" be better?

>    3. Right above Example 1.2: Here both numeric and named section
>       references are used. Since our wiki system does not support
>       automatic maintenance of section numbers when references are made,
>       I suggest that numeric references are not used.

Corrected.

>    4. Sentence right after Ex 1.2: /RIF-PRD and RIF-BLD ... in both
>       dialects./
> 
>       This is an awkward and unclear sentence. Please use something like
>       this instead:
> 
>             The condition sublanguages of RIF-PRD and RIF-BLD have much
>             in common. However, the presentation syntaxes for the rules
>             are different, largely due to the different traditions in
>             production rules and logic programing communities.
>             Nevertheless, XML serializations of these syntaxes, again,
>             have much in common, so many XML documents are valid in both
>             dialects and have the same meaning.

That was not exactly the intended meaning (so, the original sentence was, indeed, unclear). I rephrased that as:

"The condition languages of RIF-PRD and RIF-BLD have much in common, including with respect to their semantics. Although their abstract syntax and their semantics for rules are different, due to the operational nature of the conclusions in production rules, their is a subset for which they are equivalent. For that subset, the XML syntax is common, so many XML documents are valid in both dialects and have the same meaning."


>    5. Sec 2.1.1, Abstract syntax: parenthesis is missing at the end of
>       the 2nd bullet.

Corrected.

>    6. 2nd sentence after the bullets: /That notation is not ... XML
>       syntax./
> 
>       Please replace with: /This notation is not intended to be a
>       concrete syntax, and so it leaves out many details. The only
>       concrete syntax for RIF-PRD is its XML syntax./

Why not. What is wrong about the original sentence ("That notation is not intended to be a concrete syntax and it leaves out many details that are not needed for its purpose: the only concrete syntax for RIF-PRD is the XML syntax")?

>    7. Next paragraph, last sentence: / This is one of two points ...
>       languages also use./
> 
>       An unclear sentences. Please rephrase.

Rephrased as: "RIF-BLD specifies, in addition, a construct to denote logic functions, which RIF-PRD does not require: this is one of two differences between the alphabets used in the condition languages of RIF-PRD and RIF-BLD." Is that better?
> 
>    8. Sec 2.1.1.2 Atomics: The terms /atomics/ and /atomic/ are awkward
>       when used as nouns. This often leads to awkward, ungrammatical, or
>       unclear sentences. Worse yet, it seems to me that /atomics/ and
>       /atomic formulas/ are the same, so you introduce two terms for one
>       notion.

Yes, atomic and atomic formula are the same.  We took that usage of atomic from an ealier version of BLD, I guess :-)

I corrected that in the whole document (I hope I did not miss too many).

>    9. Section 2.1.1.4, well-formed formulas.
> 
>       This section was copied from BLD at the time when it had a
>       problem. The context of individuals was not defined at the time,
>       and there was an inconsistency in the definition of the context
>       for the nullary symbols of the form f(). This has now been fixed
>       in BLD, so please transfer the changes from there.

Done. Btw, in the BLD def of a well-formed formula, the square is at the end of the but last bullet item.

>   10. Section 2.1.2.1, Semantic structures.
> 
>       For production rules you need to use Herbrand domains. Otherwise,
>       the definition of the models would be broken (as it is right now).
>       PRD uses inflationary semantics for negation, and using general
>       domains is problematic in this context.
> 
>       Since BLD's semantics maps everything into the domain (including
>       predicate formulas), the domain for PRD's semantic structures
>       should consist of all terms, all atomic formulas, plus all the
>       domains for the data types.


Do you mean that just replacing the sentence "here D is a non empty set of elements called the domain of I" by "Here, D is the non empty set of all terms, all atomic formulas and the union of all the domains for the data types" would do the trick?


>   11. Definition of truth valuation, the equality bullet. In the line
>       that defines I_truth replace "if and only if" with "if" (because
>       of the "otherwise" clause that follows).

Oh, right! Corrected.

That's all for now.

I think Adrian will follow suite with 12 and 13.

I will look at your comments re the operational semantics and come back to you later.

Thanx again for the thorough and useful comments.

Christian

>   12. Sec 2.1.2.3, definition of condition satisfaction.
> 
>       This definition is incorrect, if you have PRD negation. If Ψ has
>       negation, for instance, And(p not q) then this definition is not
>       strong enough to ensure that, say, p |= And(p not q).
> 
>       What production systems do is different from logical entailment.
>       You are constructing semantic Herbrand structures instead. You
>       start with the Herbrand semantic structure that satisfies all the
>       facts and nothing else, find a rule whose premises are all true in
>       that structure, and then you fire the head of the rule. This
>       creates a new structure, and so on. In fact, I do not think that
>       you need the motion of logical entailment in the first place. You
>       do need the notion of condition satisfaction, but it should be
>       satisfaction in particular Herbrand structures, *not* the notion
>       that you are defining. (The current document defines entailment of
>       conditions by ground facts, not the notion of satisfaction in
>       semantic structures.)
> 
>   13. Definition of matching substitution.
> 
>       This definition seems broken, and is an overkill in any case. Why
>       not simply define it as σ(Ψ) ⊆ Φ?
> 
>   14. Sec 2.2.1, Abstract syntax, last paragraph. This repeats the
>       sentence that already appears in Sec 2.1.1 (after the bullets).
>   15. Sec 2.2.2, Operational semantics.
> 
>       Here the reader starts to run into notational problems. At least,
>       I did, especially trying to get through the definitions that use
>       symbols defined a page or two ago. For instance, L is used for
>       actions, W is used for ground condition formulas, T for terminal
>       states, etc. These sometimes occur with subscripts. At some point
>       it becomes hard to follow. I suggest that better mnemonic symbols
>       are used. For instance, gActions, FinalStates, gConds, etc.
> 
>   16. Definition of the PRD transition relation (Sec 2.2.2).
>           * Here φ is a ground formula, right? Say this in the preamble
>             of the definition.
>           * In the assert and retract action bullets, why not simply say
>             that w' = w+φ and w' = w - φ, respectively? This is not only
>             simpler, but also correct. In contrast, the current
>             definitions are wrong because of the problem with |= in the
>             presence of negation, as mentioned previously.
>           * In item 3, why not simply write w' = w
>             -{f1,...,fn,m1,...,mn'}? (for the same reason)
>   17. Sec 2.3.1, last sentence: repeats the same sentence in Sec 2.1.1
>       for the third time.
>   18. Sec 2.3.1.1, Rules. Sentence after the bullets: replace "noted"
>       with "written as" and delete "logic programming" (just "RIF-BLD
>       notation" is good enough).
>   19. Last paragraph in Sec 2.3.1.1: "whenever they have the same XML
>       syntax."
> 
>       This is rather indirect and looks cryptic. I'd like to also add
>       that this happens when the only actions are asserts, and there is
>       no negation.
> 
>   20. Sec 2.3.1.2, groups.
> 
>       Here the term "strategy" is used, but it was never defined, even
>       syntactically. I presume that here it must be a strategy
>       identifier. But what is its syntax? Is it a constant? a Unicode
>       string of chars? something else?
> 
>   21. Sec 2.3.1.3, def of well-formed rules: /...has a subclass atomic
>       as its target/.
> 
>       Cannot quite figure out what this is supposed to mean. An atomic
>       subclass formula? This is one of the cases where the use of
>       /atomic/ garbles the sentence. In other cases the use of this term
>       as a noun is just awkward.
> 
>   22. Sec 2.3.2, 1st line: PRS. Make it bold italic so that people could
>       find its definition more easily.
>   23. /The idea of describing PRS as a labeled ... which execution
>       results ..."/
> 
>       Replace /which/ by /whose/.
> 
>   24. Ex 3.1, 3d bullet.
> 
>       Not clear which Joe is meant: Joe the Hen or Joe the chicken.
> 
>   25. After the example: definition of rule instance.
> 
>       Mark it as a definition so that it would be easier to find.
> 
>   26. In the rule instance definition: r^id .
> 
>       What is this thing that is uniquely identifying the rule? Is it
>       the rule itself? You never talked about these identifiers before.
>       Furthermore, why not define ground instances of the rules in the
>       usual way, i.e., as the result of substitution of ground terms for
>       variables?
> 
>   27. Three paragraphs later: FORMULAE. This symbol has never been
>       defined. Why not just say "ground facts" here? The end of this
>       sentence is garbled: /... are fired, in some sense to be further
>       specified, in that state of facts/. Please rephrase.
>   28. Two paragraphs down, the definition of history.
> 
>       It is confusing and unnecessary to write histories backwards.
>       There is no advantage in making them into stacks, and this
>       assumption does not seem to be used anywhere. So, it is just
>       another distraction for the reader in a place where it is already
>       hard to read.
> 
>   29. Definition of INSTANTIATE, end of sentence: / in a sense that is
>       determined by the specification of the function./
> 
>       Cannot understand what is meant here.
> 
>   30. Definition of PICK.
> 
>       What is "input strategy" (input to what?)? A conflict resolution
>       strategy?
> 
>       The last two lines in that definition are unclear. Please rephrase.
> 
>   31. Paragraph after the FINAL bullet.
> 
>       The symbol ACTIONS has not been defined. Moreover, the definition
>       of extractActions is not clear to me.
> 
>   32. Definition of PRS_RS,LS
> 
>       Please remind what T_RS,LS is. (Earlier I suggested to use better
>       mnemonics, which would have made such reminders less important.)
> 
>       Same definition, bullet 3: (h,s h') - a missing comma.
> 
>   33. Sec 2.3.2.1, INSTANTIATE.
> 
>       Here you are talking about rule instances as things obtained from
>       rules by substituting terms for variables. This is how I also
>       suggested to define rule instances before. However, your
>       definition is different, and so here you are using the term /rule
>       instance/ in a possibly different sense. This is confusing and
>       most likely is unnecessary.
> 
>   34. Later in the same section: using the symbols ACTION and FORMULA,
>       which were not defined previously.
>   35. Definition of instantiateRULE.
> 
>       Here you are using the construct rule(r^ri ). What is this?
>       Earlier you defined only rule(ri).
> 
>   36. A few lines below: a state is a triple (w,rs,ri).
> 
>       Earlier you defined states to be pairs.
> 
>   37. A few lines below, right above Example 3.4.
> 
>       What are these "input" and "output" functions? At this point I
>       felt that it does not make sense to continue reading until all the
>       above issues are resolved.
> 
Received on Tuesday, 2 December 2008 13:46:50 GMT

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