Polynomial time algorithms for computing a representation for minimal unsatisfiable formulas with fixed deficiency
We say a propositional formula F in conjunctive normal form is represented by a formula H and a homomorphism φ, if φ(H) = F. A homomorphism is a mapping consisting of a renaming and an identification of literals. The deficiency of a formula is the difference between the number of clauses and the number of variables. We show that for fixed k ≥ 1 and t ≥ 1 each minimal unsatisfiable formula with deficiency k can be represented by a formula H with deficiency t and a homomorphism and such a representation can be computed in polynomial time.

title: On Models for Quantified Boolean Formulas
abstract: A quantified Boolean formula is true, if for any existentially quantified variable there exists a Boolean function depending on the preceding universal variables, such that substituting the existential variables by the Boolean functions results in a true formula. We call a satisfying set of Boolean functions a model. In this paper, we investigate for various classes of quantified Boolean formulas and various classes of Boolean functions the problem whether a model exists. Furthermore, for these classes the complexity of the model checking problem – whether a set of Boolean functions is a model for a formula – will be shown. Finally, for classes of Boolean functions we establish some characterizations in terms of quantified Boolean formulas which have such a model. For example, roughly speaking any satisfiable quantified Boolean Horn formula can be satisfied by monomials and vice versa.

title: Fixed-parameter tractability of disjunction-free default reasoning
abstract: In this paper, the parameter which is the source of the complexity of disjunction-free default reasoning is determined. It is shown that when the value of this parameter is fixed, the disjunction-free default reasoning can be solved in time bounded by a polynomial whose degree does not depend on the parameter. Consequently, disjunction-free default reasoning is fixed parameter tractable.

title: On the structure of some classes of minimal unsatisfiable formulas
abstract: We investigate classes of minimal unsatisfiable formulas which are closed under splitting. For marginal formulas the equivalence to some natural classes of formulas is proved. Further, we show that maximal formulas are closely related to the so-called hitting formulas. That are formulas for which any two clauses contain a pair of complementary literals.

title: On Odd and Even Cycles in Normal Logic Programs
abstract: An odd cycle of a logic program is a simple cycle that has an odd number of negative edges in the dependency graph of the program. Similarly, an even cycle is one that has an even number of negative edges. For a normal logic program that has no odd cycles, while it is known that such a program always has a stable model, and such a stable model can be computed in polynomial time, we show in this paper that checking whether an atom is in a stable model is NP-complete, and checking whether an atom is in all stable models is co-NP complete, both are the same as in the general case for normal logic programs. Furthermore, we show that if a normal logic program has exactly one odd cycle, then checking whether it has a stable model is NP-complete, again the same as in the general case. For normal logic programs with a fixed number of even cycles, we show that there is a polynomial time algorithm for computing all stable models. Furthermore, this polynomial time algorithm can be improved significantly if the number of odd cycles is also fixed.

title: Finding anchors for genomic sequence comparison
abstract: Recent sequencing of the human and other mammalian genomes has brought about the necessity to align them, to identify and characterize their commonalities and differences. Programs that align whole genomes generally use a seed-and-extend technique, starting from exact or near-exact matches and selecting a reliable subset of these, called anchors, and then filling in the remaining portions between the anchors using a combination of local and global alignment algorithms, but their choices for the parameters so far have been primarily heuristic. We present a statistical framework and practical methods for selecting a set of matches that is both sensitive and specific and can constitute a reliable set of anchors for a one-to-one mapping of two genomes from which a whole-genome alignment can be built. Starting from exact matches, we introduce a novel per-base repeat annotation, the $Z$-score, from which noise and repeat filtering conditions are explored. Dynamic programming-based chaining algorithms are also evaluated as context-based filters. We apply the methods described here to the comparison of two progressive assemblies of the human genome, NCBI build 28 and build 34 http://genome.ucsc.edu), and show that a significant portion of the two genomes can be found in selected exact matches, with very limited amount of sequence duplication.

title: Supporting Mobility in MosquitoNet
abstract: The goal of the MosquitoNet project is to provide continuous Internet connectivity to mobile hosts. Mobile hosts must be able to take advantage of the best network connectivity available in any location, whether wired or wireless. We have implemented a mobile IP system that supports seamless switching between different networks and communication devices. In contrast to previous approaches to mobile IP, we believe mobile hosts should not assume any explicit mobility support from the networks they visit, aside from basic Internet connectivity. This decision places extra responsibilities on the mobile hosts themselves. In this paper, we describe the design and implications of such a system. Measurements of our implementation show that the inherent overhead to switch networks (below 10ms) is insignificant compared to the time required to bring up a new communication device.

title: Model Checking Dynamic UML Consistency
abstract: UML is widely accepted and extensively used in software modeling. However, using different diagrams to model different aspects of a system brings the risk of inconsistency among diagrams. In this paper, we investigate an approach to check the consistency between the sequence diagrams and statechart diagrams using the SPIN model checker. To deal with the hierarchy structure of statechart diagrams, we propose a formalism called Split Automata, a variant of automata, which is helpful to bridge the statechart diagrams to SPIN efficiently. Compared with the existing work on model checking UML which do not have formal verification for their translation from UML to the model checker, we formally define the semantics and prove that the automatically translated model (i.e. Split Automata) does simulate the UML model. In this way, we can guarantee that the translated model does represent the original model.

title: Type Checking Choreography Description Language
abstract: The Web Services Choreography Description Language (WS-CDL) is a W3C specification developed for the description of peer-to-peer collaborations of participants from a global viewpoint. Currently WS-CDL has no rigorous static type checking. We believe that introducing a type system will exclude many design and description errors, and ensure desirable properties of the choreography specifications. In this paper, we took a core language CDL, which covers most of the important features of the WS-CDL, and is more convenient for the study. We developed the abstract syntax and operational semantics of CDL, and defined a collection of rules which can be used to check if choreography is well-typed. Moreover, we also proved some type safety theorems for CDL in the sense that well-typed choreography cannot get stuck. We show how the use of type information can allow us to gain confidence in the correctness of choreography.

title: An approach to hardware/software partitioning for multiple hardware devices model
abstract: Computer aided hardware/software partitioning is one of the key challenges in hardware/software co-design. This paper describes a new approach to hardware/software partitioning for multiple hardware-devices model. The partitioning is transformed into a reachability problem of timed automata, and the optimal solution can be obtained by means of an optimal reachability algorithm. To relax the initial condition of partitioning for optimization, two algorithms are designed to explore the dependency relations among processes in the sequential specification. Some experiments are conducted with model checker UPPAAL to show our approach is both effective and efficient.