Karunatillake's Thesis - Chapter 3

My first set of questions sent to Nishan C. Karunatillake regarding chapter 3 of his thesis:

Thanks for the response.

Sorry if my questions are really technical/low-level. It's just that I am developing a model for multi-agent argumentative negotiation, I came across your work and I am trying to see if my model could map to your language, protocol etc. I have not read beyond Chapter 3 yet, so I apologise if some of my questions are answered later. Please let me know if that is the case.

I'll try ask only a few questions at a time, as occurred to me whilst working sequentially through the chapter, so as not to bombard you and in case questions that occurred later become clear.

Here goes...

- Looking at the 'Challenge' communicative predicate described as part of the protocol (page 79), one of the pre-conditions for challenging a rejection (or assertion) is that there be no 'reason' for the rejection (assertion respectively) in the agent's knowledge-base. Could it not be possible (in the context of this thesis) that there is a reason for rejecting, as well as a (counter-)reason for not rejecting in the agent's knowledge-base at the same time? Or is it meant here that 'the reason for rejecting' is stronger than 'the reason for not rejecting' in an argumentative semantic/heuristic sense?

- Also, the only valid response following a Challenge is for the other agent to Assert the justification (H). Could it not be possible (in the context of this thesis) for the agent that is to respond to *not* have a justification? What if the agent has no justification (if possible), how would the dialogue then proceed? What is meant by justification - that the justification is 'valid' according to the agent's knowledge-base, or is justification here meant more simply in a kind of deductive sense?

Hope that makes sense.

The response...

I see. I reckon it should be not that difficult. You may need to define your own domain language (one that describes your context or argumentation schema/modal). Then link that domain language with the comm. language and protocol defined in the thesis. If you wish to do this formally, then, you might need to alter some of the rules of the axiomatic and operational semantics to suit your application.

OK. Before I get to your specific question, I would recommend you to read the AIJ paper, which followed this thesis (instead of the thesis). This is better than reading the version in the thesis, as I introduced some minor alterations afterwards to both the axiomatic semantics and the operational semantics. Since AIJ doesn't allow on-line appendices we also published the complete semantics as a different technical paper. The links to both these documents are:

AIJ paper - http://users.ecs.soton.ac.uk/nnc/docs/aij09.pdf
Tech report - http://eprints.ecs.soton.ac.uk/16851/2/techreport.pdf

Now to your question.

In defining the comm. language I used a notion similar to operation overloading. In other words, certain language predicates are used for more than one, similar, but not identical, purpose. The objective is to limit the number of language predicates and not unnecessarily duplicate. For instance both the proponent and respondent can use the Open-Dialogue predicate, but they would have different pre- and post- conditions. Thus, the distinction becomes clear at the semantics level (both axiomatic and operational semantic level) and not necessarily at the syntax level. Both Challenge and Assert are used this way. In particular, Challenge locution can be used for two purposes (i) by the proponent to challenge the reason for rejecting a proposal (ii) by either the proponent or respondent to challenge the reason for a particular assertion. This is also there in the use of Assert, Close-Dialogue locutions.

Q1

As mentioned above, Challenge is used for two purposes. This question, as I understand it, is related to the first purpose, Challenging the reason for rejection (the second being Challenging a particular Assertion)

In more detail, the respondent may chose to either accept a particular proposal or reject it. This decision is based on the respondent's R2 decision mechanism (see page 951 on the AIJ paper or page 85 on the thesis).

Yes, you are right the respondent may have zero or more reasons for accepting a particular proposal and also zero or more reasons for rejecting. The decision is based on which is the more compelling reason.

My agents are computational agents who attempts to maximise utility. So, they calculate what is the cost vs benefit in this proposal. If the benefit is more accept otherwise reject. From an argumentation sense this can be if the reason(s) for accepting is more stronger than the reason(s) for rejecting accept otherwise reject.

So when the proponent Challenges (the reason for rejecting a particular proposal), the respondent will pass on its reason(s). It would say it was compelled to reject because of this and this reason (to reject) was much stronger than this and this reason (to accept).

If this reason is in conflict with the Proponent's knowledge-base, then the dialogue may shift an persuasive dialogue trying to correct any inconsistencies in each others reasons (proponents reasons why the proposal should be accepted vs respondents reasons on why it was rejected).

Q2

Yes, the only valid response to a Challenge locution is an Assert. See also Figure 4 (page 948 in the AIJ) and in more detailed level Figure B1 (page 979 in the AIJ).

Case 1: If the challenge was a challenge the reason for reject, then that reason is asserted. In my context, it would say I believe the benefit of the proposal due to this and this reason is this, but the cost of accepting this proposal due to this and this reason is this. So cost is higher than the benefit. Thus, the reason for rejection.

Case 2: If the challenge was the justification for a particular assertion he has made, then the reason behind such an assertion will be returned. This follows the schema in the form of deductive equations (5) and (6) in page 943 if the AIJ.

Yes, theoretically the reason can be null.

In the first case, may simply mean, of reason for rejection, I don't have any reason to accept (no reward), so I rejected. It doesn't make much complication. The proponent will analyse why it thinks it should accept (proponent's reason, if he have any) vs this given null reason from the respondent. If there is a conflict, argue that (why for instance he may have misunderstood the reward) or give an alternative proposal with a reward.

In the latter case, may mean, I don't have a reason for asserting X, but I believe X to be true. Again the other party will compare this with its own reason (why X should be false) and will either argue to correct the oponents' knowledge or correct its own knowledge.

Hope this clarifies things a bit.

Will continue skimming through the thesis anyway, despite the suggestion otherwise, before moving on to check out the journal paper and technical report.