Today

Several contributions have accumulated since the previous issue.

1. The article by Michael Thielscher, "A Theory of Dynamic Diagnosis", has been accepted to the ETAI following two positive referee reports. One of the referees has made a few suggestions for changes to the article; these suggestions follow below and have been posted on the article's interaction page.

2. Antonis Kakas and Rob Miller have answered to the questions and suggestions by the referees to their article, "Reasoning about Actions, Narratives and Ramification" which was recently accepted to the ETAI. Their answers follow below and have been posted as usual.

3. In the light of the refereeing of those two articles, the present Newsletter editor comments on (1) the open relationship between authors, referees, and readership in the ETAI, (2) how should the advent of electronic publication and communication change our expectations as to how scientific articles ought to be written.

4. The debate about ontologies of time continues with contributions by Sergio Brandano, Pat Hayes, and Jixin Ma.

Meta-Debates

Erik Sandewall:

Two more articles have now been accepted to the ETAI after an extended period of open review discussion followed by confidential refereeing. At this point, I wish to raise some possibly controversial questions that relate to the referee reports, namely: Is it necessarily the case that articles that are published in this on-line and networked medium ought to be written in exactly the traditional style? Maybe the classical advise for How To Write A Scientific Article ought to be amended somewhat?

Note however that I am not going to propose using hypertext in extremis, or any other revolutionary new ideas. On the contrary, I believe it's important that articles continue to have their traditional look and feel from a typograhpic point of view, and that both authors and readers feel comfortable with our way of doing things. Reasonable changes to a moderate extent is the key. However, the present topic is revolutionary in another sense: you don't usually question the opinion of a referee. Only the transparency policy of ETAI makes it possible. Before I proceed on that topic, first a few words of introduction and background.

The rate of articles in ETAI is not yet very high, but this is not a problem. Since we are using a novel publication paradigm, it is in fact very useful that we get enough time for analysis and discussion with the peer communities before a larger flow of articles begins to come. We also don't have any quota where a certain number of hundred pages have to be filled each year: our publication scheme is completely elastic with respect to volume.

One of the characteristic and unique features of the ETAI is the egalitarian relationship between all actors, including between reviewers and authors. The reviewer/referee in a traditional journal habitually assumes the pose of ultimate authority, and review reports tend to use phrases such as "the article is lacking in the following respects", "the author should better explain how his (her) approach is able to deal with the following problem", and so on. Behind these phrases there is one of our colleagues, and if we met face to face she (he) would not of course use this way of talking.

In the ETAI, open discussion is the basic idea. Ideally, all feedback to the authors should occur in the open debate, and referees should only vote "accept" or "don't accept". In practice, it turns out that several of the referees get to think of possible improvements to the article as well, but even in this case their suggestions are written in the same collegial style as is used in the open discussion. Please take a look at the comments by "Anonymous Referees" for the articles by Thielscher and by Kakas and Miller for some examples of how reviewers and referees so-to-say look the authors in the eyes as they ask questions and make suggestions with respect to the article that's being considered.

It has been interesting and encouraging to see how the authors have reacted when the review comments for their articles were posted on the web, first the open discussion and then the comments by referees. Until now I have only heard positive reactions and no negative comment at all, and I do believe that the civil tone that we have adopted has contributed to that result. (Comments by the authors on this topic would be welcome!)

The intrinsic transparency of the review process gives the authors a chance to answer to the referees. It also gives the rest of us a chance to listen in to the discussion between authors and referees, and this may be very useful for understanding the contribution as well as for evaluating it. An additional advantage is that this provides an entry point to a common discussion about the topic that I mentioned in the introduction: what style ought to be used in the articles in our field. Referees are, after all, the guardians of our quality criteria, so they must be involved in any changes of practice. Thus, the following questions are posed both to the present referees, and to the whole readership.

When a referee feels that additional clarification is needed, should this automatically translate into a suggestion to amend the article? The alternative would be that the referee just asks the question, the author gets to answer it, and the question and the answer are posted in ETAI's article interaction page where they are just as easily available as the article itself. Consider, for example, the suggestions of the third referee of the Kakas and Miller article: would you rather have the answers to those questions integrated with the article, or represented separately?

I don't imagine that all reviewers' comments for all articles can best be dealt with separately, but maybe for many of them this would be appropriate. After all, dialogue tends to be more lively than monologue, and seeing what questions others have asked may be more interesting than just reading passages of an article that provide answers to untold questions.

Do networked articles need to be as self-contained as articles in the classical medium? If an article in a conventional journal forces the reader to refer to another article for essential material (such as background, motivation, or definitions) then it may be very inconvenient for the reader to find the cited material. In the on-line context this is not so: a hot link in an ENRAC-style footnote (as used in the version of ENRAC that uses frames) allows the reader to click her way instantly to the cited material. In this light, what stand do we wish to take on the third referee's suggestions for additional background material in the Kakas and Miller paper?

Naturally, my references to the referee reports is for examplification only: the refereeing for these articles has been concluded, and it's not my intention to submit the recommendations of the referees to a referendum each time an article is up for acceptance. It is also clear that the recommendations of the present referees are perfectly consistent with traditional criteria for high-quality journals in our field. It's exactly for this reason that these referee reports may also be useful as a starting point for an important discussion: can we improve the quality of form without sacrificing (and hopefully also improving) the quality of content in research articles that are published in the electronic medium, such as the ETAI?

Comments from the readership are welcome on both of these questions, as well as on the general issue of how we can make the best use of electronic communication and publication in our area of research.

ETAI Publications

Additional contributions have been received for the discussions about the following article(s). Please click the title of the article in order to see each contribution in its context.

Michael Thielscher
A Theory of Dynamic Diagnosis
   Review protocol: [in this pane]; with links: [frame] [noframe]

Antonis Kakas and Rob Miller
Reasoning about Actions, Narratives and Ramification
   Review protocol: [in this pane]; with links: [frame] [noframe]

Debates

Pat Hayes:

A comment on Sergio's reply to Jixin:

An interval from the real-line is an ordered set of real numbers limited by its end-points, which are not necessarily included in the set.

It seems from this that the set of intervals is supposed to include open, half-open and closed intervals; is that right? (Or do you mean to say that there may be some doubt about whether a particular interval does or does not include its endpoints? If the latter, this is not the usual notion of 'interval' as used in real analysis, and you need to explain further.)

Suppose  S  consists of intervals from the real line. Assume  <s1,t1> in A  and  <s2,t2> in B , intervals in  S . We say that  <s1,t1> < <s2,t2>  iff  t1 < s2 . The strict order relation   <   is an abbreviation for   < logical-and =/  .

It follows then that for intervals,   <   implies   <   except for pointlike intervals (single-point closed intervals) since if  t1 < s2 , the intervals  <s1,t1>  and  <s2,t2>  cannot be equal unless  s1 = t1 = s2 = t2 .

Suppose now that  <s1,t1> < <s2,t2> . The axiom of completeness states the existence of  xi in S  such that  <s1,t1> < xi < <s2,t2> .

Consider the closed intervals   [p, q]   and   [q, r]   with  p < q < r . These satisfy   <   and hence satisfy   <  , but there is no interval between them. Hence, your axiom is false for intervals on the real line.

Pat Hayes

Jixin Ma:

To Sergio, who wrote:

The (temporal) domain  S , as I meant, may consist either of time-points xor of time-intervals (exclusive "or"). An interval from the real-line is an ordered set of real numbers limited by its end-points, which are not necessarily included in the set. Suppose  S  consists of intervals from the real line. Assume  <s1,t1> in A  and  <s2,t2> in B , intervals in  S . We say that  <s1,t1> < <s2,t2>  iff  t1 < s2 . The strict order relation   <   is an abbreviation for   < logical-and =/  . Suppose now that  <s1,t1> < <s2,t2> . The axiom of completeness states the existence of  xi in S  such that  <s1,t1> < xi < <s2,t2> . I reply in advance to your next question: "Why did you write   <   instead of   <   ?". The reply is that   <   means "less or equal", that is  xi  may not be equal to  t1  or  s2 , but it can do so. Note that since  xi  belongs to  S , then  xi  is an interval. This is also meant as a reply to your question about the dividing instant problem. I could not penetrate the rest of your message.

First of all, what you wrote in the above didn't solve the Dividing Instant Problem at all!

Anyway, you have claimed that "The (temporal) domain S may consist either of time-points or (exclusive-or) of time-intervals", and "an interval from the real-line is an ordered set of real numbers limited by its end-points, which are not necessarily included in the set." In this case, can your intervals be "pointlike"? That is, for an interval  <s,t> , is  s  allowed to be equal to  t ? In other words, can a set representing an interval be a singleton? As I suggested in my former response, the anwser has to be yes (see below). That is, if your domain  S  contains non-pointlike intervals, then, to satisfy the so-called completeness property, the domain  S  must contains singletons (or namely points!) as well. Therefore, all my former questions for you still apply.

I have shown in my former message that if your domain  S  contains intervals, it must contain points as well. However, you claimed that  S  does not consist both of time-points and intervals since you specially claimed that your "or" is exclusive-or). I would like to use your notation to show this again.

In fact, you define the (partial) relation "  <  " as follows:  <s1,t1> < <s2,t2>  iff  t1 < s2 . Consider the case that interval  <s1,t1>  in  A  and interval  <s2,t2>  in  B , satisfying  <s1,t1> < <s2,t2> , and  t1 = s2  (this is a valid case according to your definition). To fulfil the completeness property, there exists a  xi  in domain  S  such that  <s1,t1> < xi < <s2,t2> . Let  xi = <s,t> . Again, by the definition of "  <  " between intervals, we have  t1 < s  and  t < s2 . However, remember  t1 = s2 , we infer that it is impossible for  s < t . Therefore, we reach that  s = t . That is  xi  must be a point (pointlike)!

By the way, it seems that your description of the axiom of completeness is not a first-order one.

Jixin

Sergio Brandano:

In ENRAC 24.4.1998 I made a typing mistake. I wrote: " xi  may not be equal to  t1  or  s2 , but it can do so", while it should obviously be: "assuming  xi =  <xi₁, xi₂>  , then  xi₁  may not be equal to  t1  and  xi₂  may not be equal to  s2 , but they can do so".

In reply to Jixin Ma (ENRAC 23.4 and 24.4 1998) -- completion:

So, you think intervals are not needed? Anyway, our arguments...

I am actually skeptic about the need of a temporal domain which includes time-intervals. There are many convincing arguments that a temporal domain consisting of time-points is good enough in many different situations (Newtonian mechanics and Thermodynamics, for instance, as well as Sandewall's underlying semantics for  K-IA ), and I see no reason why I should pursue a different path.

... about the convenience of using intervals are based on the belief of the need of them.

This is why I originally asked for some convincing argument(s) for the plausibility of this approach. According to the standard scientific methodology, in fact, we shall build on top of already existent solutions, and be consistent. Just to make an example, suppose one refuses a classical notion (continuity?), and encounters the problems that this notion was used to solve (the dividing instant?); it is surely not consistent to justify the need for a novel approach via the claim that the problems he encountered can not be solved by the notion he just refused. The notion of semi-continuity, for instance, has dignity, and its plausibility is far to be based on the belief that continuity is not needed... The case of time-intervals is clearly safer; one may simply give a preliminary example and show some objective advantages when using time-intervals instead of time-points.

Premise: It is evident that if you assume the axiom of completeness, the domain  S  can just be continuous, while if you do not assume the axiom of completeness then  S  is necessarily discrete.

Wrong! Even if you do not asssume the axiom of completeness, it is still not nessarily discrete.

Yes, I agree. I realize I wrote that sentence having in mind the basic time structure on my paper. The question holds properly if you do not assume any axiom of density other than the one I stated.

Concerning the dividing instant problem, which seems to summarize what is left from your objections, please read below.

In reply to Pat Hayes (ENRAC 24.4.1998):

As posted in my original message, I have not yet seen any explanation why an alternative notion of continuous structure is needed at all?

Probably, in order to prevent any misunderstanding, I should have included an additional sentence like "... is needed at all, within the search of those non-monotonic logics which purpose is to formalize common sense reasoning when reasoning about actions and change", but I thought it was evident, as the title of this Newsletter reminds.

In particular, in the same message, I asked to give at least one convincing argument on the need of a notion which is an alternative to the classical one, along the lines: "the problem P of temporal reasoning about actions and change can not be solved adopting the axiom of completeness", or "the axiom of completeness is too strong an assumption for our purposes; axiom A is better suited, because..." ( >>>>star )

You and Jixin Ma proposed the "dividing instant problem", apropos of the problem of switching on the light, and argued the axiom of completeness inadequate for solving that problem. The formulation I gave in ENRAC 24.4.1998, with today's minor adjustment, gives the evidence on how the axiom of completeness is, instead, safe with respect to the dividing instant problem. You and Jixin based your argument on the fact that I do not allow the domain  S  to hold points "and" intervals, so that if  S  admits just intervals then the dividing point  p  can not exist. I refuted that argument by simply observing an interval from the real line may have equal end-points.

You also gave other examples, but you did not explain how they relate to the world of "Reasoning about Actions and Change". In particular, and I somehow repeat myself, it is not evident that one needs a temporal domain with non-homogeneous continuity (let me say it is even less evident the need of the imaginary number  i  in our temporal structure). Does there exist at least one representative problem of reasoning about actions and change that can not be solved adopting the axiom of completeness, so that to justify a temporal domain with non-homogeneous continuity? (and I repeated ( >>>>star ))

You also gave an informal argument on the plausibility of a temporal structure which formalizes the perceived smooth flux and perceived fast flux of time (ENRAC 21.4.1998). I refuted that plausibility with my contribution to ENRAC 23.4.1998.

(Is it really ``free of context'' to you ?)

Best Regards
Sergio