A self-adaptable scheduler for synchronizing transactions in dynamically configurable environments

In a database system, the scheduler has the goal of synchronizing operations belonging to several concurrent transactions. The scheduler implements a concurrency control protocol, which may have either conservative or aggressive behavior. Existing database systems have schedulers with static behavior. This paper presents a self-adaptable scheduler, called Intelligent Transaction Scheduler (ITS), which has the ability of dynamically changing its behavior to adapt itself to the characteristics of the computing environment, without any human interference by using an expert system based on fuzzy logic. ITS can implement different correctness criteria, such as classical (syntactic) serializability and semantic serializability.     

Profitable and dynamically feasible operating point selection for constrained processes

The operating point of a typical chemical process is determined by solving a non-linear optimization problem where the objective is to minimize an economic cost subject to constraints. Often, some or all of the constraints at the optimal solution are active, i.e., the solution is constrained. Though it is profitable to operate at the constrained optimal point, it might lead to infeasible operation due to uncertainties. Hence, industries try to operate the plant close to the optimal point by “backing-off” to achieve the desired economic benefits. Therefore, the primary focus of this paper is to present an optimization formulation for solving the dynamic back-off problem based on an economic cost function. In this regard, we work within a stochastic framework that ensures feasible dynamic operating region within the prescribed confidence limit. In this work, we aim to reduce the economic loss due to the back-off by simultaneously solving for the operating point and a compatible controller that ensures feasibility. Since the resulting formulation is non-linear and non-convex, we propose a novel two-stage iterative solution procedure such that a convex problem is solved at each step in the iteration. Finally, the proposed approach is demonstrated using case studies.     

Effective synchronizing algorithms

The notion of a synchronizing sequence plays an important role in the model-based testing of reactive systems, such as sequential circuits or communication protocols. The main problem in this approach is to find the shortest possible sequence which synchronizes the automaton being a model of the system under test. This can be done with a synchronizing algorithm. In this paper we analyze the synchronizing algorithms described in the literature, both exact (with exponential runtime) and greedy (polynomial). We investigate the implementation of the exact algorithm and show how this implementation can be optimized by use of some efficient data structures. We also propose a new greedy algorithm, which relies on some new heuristics. We compare our algorithms with the existing ones, with respect to both runtime and quality aspect.     

On synchronizing unambiguous automata

We give a polynomial upper bound for the length of the shortest word of minimal rank in a transitive n-state unambiguous automation whose transition monoid does not contain the null relation. In particular, in an n-state synchronizing unambiguous automation there is a synchronizing word of length less than .     

Methods of synchronizing digital watermarks

Various methods of synchronizing digital watermarks are described and compared. The methods are grouped into the following two categories: compensation of geometric distortions and extraction of an invariant domain. The methods considered are as follows: template matching, self-reference watermarking, and feature point methods, methods based on the Radon transform, and invariant extraction by means of the Fourier-Mellin transform. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 1, pp. 180–188, January–February 2008.     

Shortest synchronizing strings for Huffman codes

Most complete binary prefix codes have a synchronizing string, that is a string that resynchronizes the decoder regardless of its previous state. This work presents an upper bound on the length of the shortest synchronizing string for such codes. Two classes of codes with a long shortest synchronizing string are presented. It is known that finding a synchronizing string for a code is equivalent to finding a synchronizing string of some finite automaton. The Černý conjecture for this class of automata is discussed.     

A comparison of two synchronizing concepts

Summary In this paper the use of semaphores and critical regions to synchronize concurrent processes is compared to a more recent proposal for so-called conditional critical regions. The latter concept permits the programmer to express directly that a process must be delayed until a certain condition holds before entering a critical region. The paper describes a well-structured notation for these. synchronizing concepts and uses both of them to solve a typical resource allocation problem. The two solutions are compared by outlining proofs of their correctness. A fairly long argument is needed to justify the solution which uses semaphores. In contrast, the solution based on conditional critical regions is so obvious that a proof is hardly needed. The paper concludes by explaining why programs using semaphores in general will be much more obscure than programs using conditional critical regions.I wish to thank Tony Hoare for many inspiring conversations on parallel programming.     

An adaptive protocol for synchronizing media streams

Stream synchronization is widely regarded as a fundamental problem in the field of multimedia systems. Solutions to this problem can be divided into adaptive and rigid mechanisms. While rigid mechanisms are based on worst case assumptions, adaptive ones monitor the underlying network and are able to adapt themselves to changing network conditions. In this paper, we will present an adaptive stream synchronization protocol. This protocol supports any kind of distribution of the sources and sinks of the streams to be synchronized. It is based on a buffer-level control mechanism, allowing immediate corrections when the danger of a buffer overflow or underflow is recognized. Moreover, the proposed protocol is flexible enough to support a wide variety of synchronization policies, which can be dynamically changed while synchronization is in progress. Finally, the message overhead of this protocol is low, because control messages are only exchanged when network conditions change.     

Improved upper bounds on synchronizing nondeterministic automata

We show that i-directable nondeterministic automata can be i-directed with a word of length O(2ⁿ) for i=1,2, where n stands for the number of states. Since for i=1,2 there exist i-directable automata having i-directing words of length Ω(2ⁿ), these upper bounds are asymptotically optimal. We also show that a 3-directable nondeterministic automaton with n states can be 3-directed with a word of length , improving the previously known upper bound O(2ⁿ). Here the best known lower bound is .     

Counting Beans

Our current body politic is looking for a more robust voting mechanism that is secured by technology rather than by the competence and integrity of bean counters.     

Adapting object-communication methods dynamically

When objects migrate or are reused, they must find suitable existing objects and establish communication with them. The authors describe the first stage of Omega, a model that lets developers dynamically adjust object-communication methods so that new and existing objects can exchange messages     

Reading dynamically displayed text

Sixty four members of the public were exposed to the same staged conversation either while waiting in a bus station or travelling on a train. Half of the conversations were by mobile phone, so that only one end of the conversation was heard, and half were co present face-to-face conversations. The volume of the conversations was controlled at one of two levels: the actors' usual speech level and exaggeratedly loud. Following exposure to the conversation participants were approached and asked to give verbal ratings on six scales. Analysis of variance showed that mobile phone conversations were significantly more noticeable and annoying than face-to-face conversations at the same volume when the content of the conversation is controlled. Indeed this effect of medium was as large as the effect of loudness. Various explanations of this effect are explored, with their practical implications.     

Reading dynamically displayed text

Two experiments were carried out to find an optimal electronic text display method given limited display space. The display formats tested fell into two categories: Times Square, in which text is scrolled from right to left; and rapid, serial, visual presentation (RSVP), in which text is presented one or several words at a time to a fixed location in the display. Previous studies have indicated that Times Square format is not as efficient as page format display or, by extrapolation, as RSVP. These studies, unlike the present experiments, did not include a smooth-scrolling (pixel-by-pixel) condition. In Experiment 1, a comparison was made between multiple-word RSVP and three versions of Times Square format, differing only in the size of steps by which the display was scrolled. Except for the largest step-size, comprehension was as high in the Times Square conditions as in the RSVP condition. The subjects expressed a significant preference for smooth scrolling Times Square over any other condition. Experiment 2 showed that comprehension for smooth scrolling Times Square was at least as high as that for RSVP at presentation rates ranging from 100 to 300 words per minute. Times Square reading is discussed in terms of optokinetic nystagmus (OKN).     

Synchronizing automata with finitely many minimal synchronizing words

A synchronizing word for a given synchronizing DFA is called minimal if none of its proper factors is synchronizing. We characterize the class of synchronizing automata having only finitely many minimal synchronizing words (the class of such automata is denoted by FG). Using this characterization we prove that any such automaton possesses a synchronizing word of length at most 3n-5. We also prove that checking whether a given DFA A is in FG is co-NP-hard and provide an algorithm for this problem which is exponential in the number of states A.     

The implementation of synchronizing operations in various environments

Since E. W. Dijkstra's work on the mutual interdependencies of co-operating sequential processes there has been much discussion on various synchronizing mechanisms. This discussion usually leads to abstract definitions of synchronizing primitives. However, their realization proceeds differently in various environments. Length of critical regions, number of processors, and dispatching strategy have to be taken into account. In this paper is presented a family of synchronizing operations, the members of which are all based on the same fundamentals. They have been designed with the concept of structured programming in mind.