Compilation d'un langage de planification temporelle de haut niveau en PDDL2.1

Session "Articles"National audienceEn planification, la puissance d'expression du langage dans lequel on exprime les instances des problèmes est importante. Un langage riche avantage l'utilisateur lorsqu'il doit encoder ses problèmes alors qu'un langage simple avantage le programmeur qui doit implémenter un planificateur capable de résoudre tous les problèmes pouvant être exprimés dans ce langage. Considérant le langage de planification temporelle PDDL 2.1 comme un langage de bas niveau, nous montrons ici comment compiler automatiquement un langage plus riche en PDDL 2.1. Dans le pire des cas, la complexité de notre transformation est quadratique. Notre langage de haut niveau permet à l'utilisateur de créer des time-points et d'imposer des contraintes temporelles simples entre eux. Les conditions et effets des actions peuvent leur être associés ainsi qu'à des intervalles et à des intervalles flottants à l'intérieur d'intervalles fixes. Notre langage permet également de modéliser des transitions non-instantanée

Monotone Temporal Planning : tractability, extensions and applications (Extended abstract)

International audienceWe describe a polynomially-solvable class of temporal planning problems. Polynomiality follows from two assumptions. Firstly, by supposing that each fluent (fact) can be established by at most one action, we can quickly determine which actions are necessary in any plan. Secondly, the monotonicity of fluents allows us to express planning as an instance of STP ≠  (Simple Temporal Problem with difference constraints). This class includes temporally-expressive problems requiring the concurrent execution of actions, with potential applications in the chemical, pharmaceutical and construction industries. Any (temporal) planning problem has a monotone relaxation, which can lead to the polynomial-time detection of its unsolvability in certain cases. Indeed our relaxation is orthogonal to the relaxation based on ignoring deletes used in classical planning since it preserves deletes and can also exploit temporal information

Temporal Constraint Satisfaction Problems and Difference Decision Diagrams: A Compilation Map

International audienceThe frameworks dedicated to the representation of quantitative temporal constraint satisfaction problems, as rich as they are in terms of expressiveness, define difficult requests - typically NP-complete decision problems. It is therefore adventurous to use them for an online resolution. Hence the idea to compile the original problem into a form that could be easily solved. Difference Decision Diagrams (DDDs) have been proposed by [1] as a possible way to cope with this difficulty, following a compilation-based approach. In this article, we draw a compilation map that evaluates the relative capabilities of these languages (TCSP, STP, DTP and DDD) in terms of algorithmic efficiency, succinctness and expressiveness

Planification SAT et Planification Temporellement Expressive. Les Systèmes TSP et TLP-GP.

This thesis deals with Artificial Intelligence planning. After introducing the domain and the main algorithms in the classical framework of planning, we present a state of the art of SAT planning. We analyse in detail this approach which allows us to benefit directly from improvements brought regularly to SAT solvers. We propose new encodings integrating a least-commitment strategy postponing as much as possible the scheduling of actions. We then introduce the TSP system which we have implemented to equitably compare the different encodings and we detail the results of numerous experimental tests which show the superiority of our encodings in comparison with the existing ones. We introduce then a state of the art of temporal planning by analysing algorithms and expressiveness of their representation languages. The great majority of these planners do not allow us to solve real problems for which the concurrency of actions is required. We then detail the two original approaches of our TLP-GP system which allow us to solve this type of problem. As with SAT planning, a large part of search work is delegated to a SMT solver. We then propose extensions of the PDDL planning language which allows us to a certain extent to take into account uncertainty, choice, or continuous transitions. We show finally, thanks to an experimental study, that our algorithms allow us to solve real problems requiring numerous concurrent actions.Cette thèse s'inscrit dans le cadre de la planification de tâches en intelligence artificielle. Après avoir introduit le domaine et les principaux algorithmes de planification dans le cadre classique, nous présentons un état de l'art de la planification SAT. Nous analysons en détail cette approche qui permet de bénéficier directement des améliorations apportées régulièrement aux solveurs SAT. Nous proposons de nouveaux codages qui intègrent une stratégie de moindre engagement en retardant le plus possible l'ordonnancement des actions. Nous présentons ensuite le système TSP que nous avons implémenté pour comparer équitablement les différents codages puis nous détaillons les résultats de nombreux tests expérimentaux qui démontrent la supériorité de nos codages par rapport aux codages existants. Nous présentons ensuite un état de l'art de la planification temporelle en analysant les algorithmes et l'expressivité de leurs langages de représentation. La très grande majorité de ces planificateurs ne permet pas de résoudre des problèmes réels pour lesquels la concurrence des actions est nécessaire. Nous détaillons alors les deux approches originales de notre système TLP-GP permettant de résoudre ce type de problèmes. Ces approches sont comparables à la planification SAT, une grande partie du travail de recherche étant déléguée à un solveur SMT. Nous proposons ensuite des extensions du langage de planification PDDL qui permettent une certaine prise en compte de l'incertitude, du choix, ou des transitions continues. Nous montrons enfin, grâce à une étude expérimentale, que nos algorithmes permettent de résoudre des problèmes réels nécessitant de nombreuses actions concurrentes

Une classe traitable de problèmes de planification temporelle

National audienceCet article présente une classe de problèmes de planification temporelle solubles en temps poly- nomial. Ce résultat découle de deux hypothèses. Nous supposons d'abord que les sous-buts ne peuvent être établis que par une action unique, ce qui nous permet de déterminer rapidement les actions qui sont nécessaires dans tous les plans. Nous supposons également que les sous-buts sont monotones, ce qui nous permet d'exprimer la planification comme une instance de STP≠ (Simple Temporal Problem, difference cons- traints). Notre classe contient des problèmes temporellement expressifs, ce que nous illus- trons avec un exemple de planification de pro- cessus chimique

A simple account of multiagent epistemic planning

International audienceA realistic model of multiagent planning must allow us to model notions which are absent in classical planning such as communication and knowledge. We investigate multiagent planning based on a simple logic of action and knowledge that is based on the visibility of propositional variables. Using such a formal logic allows us to deduce the validity of a plan from the validity of the individual actions which compose it. We present a coding of multiagent planning problems expressed in this logic into the classical planning language PDDL. Feeding the resulting problem into a PDDL planner provides a provably correct plan for the original multiagent planning problem. We use the gossip problem as a running example

A fast, efficient and sequence-independent method for flexible multiple segmental isotope labeling of RNA using ribozyme and RNase H cleavage

Structural information on RNA, emerging more and more as a major regulator in gene expression, dramatically lags behind compared with information on proteins. Although NMR spectroscopy has proven to be an excellent tool to solve RNA structures, it is hampered by the severe spectral resonances overlap found in RNA, limiting its use for large RNA molecules. Segmental isotope labeling of RNA or ligation of a chemically synthesized RNA containing modified nucleotides with an unmodified RNA fragment have proven to have high potential in overcoming current limitations in obtaining structural information on RNA. However, low yields, cumbersome preparations and sequence requirements have limited its broader application in structural biology. Here we present a fast and efficient approach to generate multiple segmentally labeled RNAs with virtually no sequence requirements with very high yields (up to 10-fold higher than previously reported). We expect this approach to open new avenues in structural biology of RN

Coordination to a di-tert-butylphosphidoboratabenzene ligand with electronically unsaturated group 10 transition metals

A new boratabenzene-phosphine ligand, di-tert-butylphosphidoboratabenzene, [DTBB]−, has successfully been synthesized by reduction of the corresponding di-tert-butylchlorophosphidoborabenzene compound (2). The species was structurally characterized with both K+ (3) and 18-crown-6·K+ (4) as counterions. Reactions of two equivalents of di-tert-butylphosphidoboratabenzene with NiBr2(PPh3)2, PtCl2, and PtCl2(COD) were undertaken and were successful in yielding three new organometallic boratabenzene species, (μ-κ-η6-C5H5BP(tBu)2)2Ni2 (5), (η3-(C,B,P)-C5H5BP(tBu)2)2Pt (6), and (η3-(C,B,P)-C5H5BP(tBu)2)(κ-C8H12(P(tBu)2BC5H5)Pt (7), respectively. The di-tert-butylphosphidoboratabenzene species displays a remarkable tendency to coordinate to transition metal species in two distinct modes closely associated with other reported boratabenzene and allyl-like interactions. Also of interest is the ability for di-tert-butylphosphidoboratabenzene to be able to coordinate within monomeric as well as dimeric transition metal compounds. The synthesis and characterization will be discussed in detail along with DFT calculations in order to validate these research findings

Automated and assisted RNA resonance assignment using NMR chemical shift statistics

The three-dimensional structure determination of RNAs by NMR spectroscopy relies on chemical shift assignment, which still constitutes a bottleneck. In order to develop more efficient assignment strategies, we analysed relationships between sequence and 1H and 13C chemical shifts. Statistics of resonances from regularly Watson-Crick base-paired RNA revealed highly characteristic chemical shift clusters. We developed two approaches using these statistics for chemical shift assignment of double-stranded RNA (dsRNA): a manual approach that yields starting points for resonance assignment and simplifies decision trees and an automated approach based on the recently introduced automated resonance assignment algorithm FLYA. Both strategies require only unlabeled RNAs and three 2D spectra for assigning the H2/C2, H5/C5, H6/C6, H8/C8 and H1′/C1′ chemical shifts. The manual approach proved to be efficient and robust when applied to the experimental data of RNAs with a size between 20 nt and 42 nt. The more advanced automated assignment approach was successfully applied to four stem-loop RNAs and a 42 nt siRNA, assigning 92-100% of the resonances from dsRNA regions correctly. This is the first automated approach for chemical shift assignment of non-exchangeable protons of RNA and their corresponding 13C resonances, which provides an important step toward automated structure determination of RNA

Response of zooplankton to improving water quality in the Scheldt estuary (Belgium)

Data obtained from 14 years of monthly samplings (1996e2009) were used to investigate the response of the crustacean zooplankton community to improving water quality in the Scheldt estuary. A strong reduction of poor water quality indicators, such as NH4þ and BOD5, as well as an increase in oxygen and in chlorophyll a concentrations were observed during the study period. During the study period, important changes were observed in the zooplankton community composition and spatial distribution. From 2007 onwards, most of the calanoid population, previously mainly found in the brackish water reach of the estuary, moved to the freshwater, where they reached higher abundances than previously observed. Simultaneously, cyclopoids populations strongly decreased in freshwater while cladocerans did not change their abundance, except during years with high chlorophyll a concentrations. Redundancy analyses (RDA) showed that the variability within the calanoid population can be explained by the improvement in water quality. Variability within the cyclopoids and cladoceran community is mainly explained by chlorinity and chlorophyll a concentrations. Their presence in the most polluted upstream area until 2007 suggests they are more tolerant to poor water quality than calanoids. Several hypotheses to explain the disappearance of cyclopoids after the move of calanoids to the freshwater are presented and discussed