TY - JOUR
T1 - On the nature and role of modal truth criteria in planning
AU - Kambhampati, Subbarao
AU - Dana S, Nau
N1 - Funding Information:
Kambhampati’s research is supportedi n part by an NSF Research Initiation Award IRI-9210997, an NSF Young Investigator Award IRI-9457634, and ARPA/Rome Laboratory planning initiative under grants F30602-93-C-0039 and F30602-95-C-0247.N au’s researchi s supportedi n part by NSF grants IRI-9306580, NSF EEC 94-02384a nd ARPA grant DATB63-95-C-0037. Any opinions, findings, and conclusions or recommendations
PY - 1996/4
Y1 - 1996/4
N2 - Chapman's paper, "Planning for conjunctive goals", has been widely acknowledged for its contribution toward understanding the nature of partial-order planning, and it has been one of the bases of later work by others - but it is not free of problems. This paper addresses some problems involving modal truth and the modal truth criterion (MTC). Our results are as follows: (i) Even though modal duality is a fundamental property of classical modal logics, it does not hold for modal truth in Chapman's plans; i.e., "necessarily p" is not equivalent to "not possibly ¬p". (ii) Although the MTC for necessary truth is correct, the MTC for possible truth is incorrect: it provides necessary but insufficient conditions for ensuring possible truth. Furthermore, even though necessary truth can be determined in polynomial time, possible truth is NP-hard. (iii) If we rewrite the MTC to talk about modal conditional truth (i.e., modal truth conditional on executability) rather than modal truth, then both the MTC for necessary conditional truth and the MTC for possible conditional truth are correct; and both can be computed in polynomial time, (iv) The MTC plays a different role in plan generation than it does in checking the correctness of plans, and this has led to several misconceptions about the MTC. Several researchers have mistakenly attempted to simplify the MTC by eliminating the white-knight declobbering clause from it; and others have used Chapman's results to conjecture that partial-order planning will not scale up to more expressive action representations. We point out that these ideas are misconceptions, and explain why.
AB - Chapman's paper, "Planning for conjunctive goals", has been widely acknowledged for its contribution toward understanding the nature of partial-order planning, and it has been one of the bases of later work by others - but it is not free of problems. This paper addresses some problems involving modal truth and the modal truth criterion (MTC). Our results are as follows: (i) Even though modal duality is a fundamental property of classical modal logics, it does not hold for modal truth in Chapman's plans; i.e., "necessarily p" is not equivalent to "not possibly ¬p". (ii) Although the MTC for necessary truth is correct, the MTC for possible truth is incorrect: it provides necessary but insufficient conditions for ensuring possible truth. Furthermore, even though necessary truth can be determined in polynomial time, possible truth is NP-hard. (iii) If we rewrite the MTC to talk about modal conditional truth (i.e., modal truth conditional on executability) rather than modal truth, then both the MTC for necessary conditional truth and the MTC for possible conditional truth are correct; and both can be computed in polynomial time, (iv) The MTC plays a different role in plan generation than it does in checking the correctness of plans, and this has led to several misconceptions about the MTC. Several researchers have mistakenly attempted to simplify the MTC by eliminating the white-knight declobbering clause from it; and others have used Chapman's results to conjecture that partial-order planning will not scale up to more expressive action representations. We point out that these ideas are misconceptions, and explain why.
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U2 - 10.1016/0004-3702(94)00095-6
DO - 10.1016/0004-3702(94)00095-6
M3 - Article
AN - SCOPUS:0030124190
SN - 0004-3702
VL - 82
SP - 129
EP - 155
JO - Artificial Intelligence
JF - Artificial Intelligence
IS - 1-2
ER -