Delta compression, which consists of compactly encoding one le version as the result of changes to another, can improve eciency in the use of network and disk resources. Delta compression techniques are readily available and can result in compression factors of ve to ten on typical data. Managing delta-compressed storage, however, is a dicult task. I will present a system that attempts to isolate the complexity of delta-compressed storage management by separating the task of version labeling from performance issues. I will show how the system integrates delta-compressed transport with delta-compressed storage. Existing tools for managing delta-compressed storage suer from weak le system support. Lack of transaction support is responsible for inecient application behavior. The only atomic operation in the traditional le system forces unnecessary disk activity due to copying costs. I will demonstrate that transaction support can improve application performance and extensibility wit...

How does the Web look? How could we tell an abnormal social network from a normal one? These and similar questions are important in many fields where the data can intuitively be cast as a graph; examples range from computer networks to sociology to biology and many more. Indeed, any M : N relation in database terminology can be represented as a graph. A lot of these questions boil down to the following: "How can we generate synthetic but realistic graphs?" To answer this, we must first understand what patterns are common in real-world graphs and can thus be considered a mark of normality/realism. This survey give an overview of the incredible variety of work that has been done on these problems. One of our main contributions is the integration of points of view from physics, mathematics, sociology, and computer science. Further, we briefly describe recent advances on some related and interesting graph problems.

This paper looks into the behavior of a simple, fine-grain parallel extension of Quicksort for cache-coherent shared address space multiprocessors. Quicksoft has many nice properties: i) it is fast and general purpose; it is widely believed that Quicksoft is the fastest general-purpose sorting algorithm, on average, and for a large number of elelnents [Blelloch et al. 1991; Dusseau et al. 1996; Helman et al. 1996b; Sohn and Kodama 1998], ii) it is in-place, iii) it exhibits good cache pcrforinance and iv) it is simple to inlplelnent. The new generation of hardware-coherent, shared address space multiprocessor systems with their already donfinant position on the tightly-coupled nmltiprocessor systems are our target systems. The implementation of the parallel Quicksort algorithm utilizes the capabilities that these new systems have to or and uses the fbllowing algorithmic techniques: Cache-qcieni:. Each processor tries to use all keys when sequentially passing through the keys of a cached-block from the key array

The paper is concerned with a special problem of inductive synthesis of recursive functional programs. Starting point for induction is a complete set of example computations in a nite domain. The example computations are mainly obtained by a problem solver in form of an initial shortest path tree spanning the problem graph. It is shown that the initial tree can be automatically transformed into a finite initial program. Induction (generalization-to-n) results in a program which transforms each initial state of any problem domain which is a recursive extension of the given fiite domain into the desired output. Programs are represented in an abstract way by terms, i.e., elements of a term algebra. Thus, our approach is simultaneously an example of the design of recursive algorithms from finite cases. The core of our investigations is to detect sub-structures in the finite initial trees playing the role of "macro-functions" (sub-routines). As compared to the "macro-operators" used in planning the main point of our approach is the de nition of macros containing all cases (operation sequences) reaching the corresponding goal including the trivial one that the goal is already true in a state. A special case of macro-induction is the invention of complex (recursive) predicates. We show that in some cases induction can only be performed after the introduction of the detected macrofunctions, considering them as elementary functions in a new, extended term algebra. In the special cases considered in this paper, the programs which can be induced after the introduction of macro-functions are linear or linear recursive, i.e. have a macro-structure which cannot easily be seen in the set (tree) of initial example computations. At the end of the paper, cognitive aspects - especially con...

The multiagent plan coordination problem arises whenever multiple agents plan to achieve their individual goals independently, but might mutually benefit by coordinating their plans to avoid working at cross purposes or duplicating effort. Although variations of this problem have been studied in the literature, there is as yet no agreement over a general characterization of the problem. In this paper, we describe a general framework that extends the partialorder, causal-link plan representation to the multiagent case, and that treats coordination as a form of iterative repair of plan flaws that cross agents. We show, analytically and empirically, that this algorithmic formulation can scale to the multiagent case better than can a straightforward application of the most advanced single-agent plan coordination technique, highlighting fundamental differences between single-agent and multiagent planning.

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Autonomous mobile entity navigation through dynamic and unknown environments is an essential part of many mission critical applications like search and rescue and fire fighting. The dynamism of the environment makes it particularly difficult to achieve navigation using just on-board sensors and existing navigation methods. This motivates the integration of wireless sensor networks with navigation. The ease of deployment of a wireless sensor network along with its capability of collecting and delivering information about the surrounding environment makes it feasible to use wireless sensor networks to aid navigation in dynamic environments. In this paper, we present integrated navigation and network query strategies that achieve good navigation performance with low network communication cost. The reduced communication cost not only increases network lifetime but also improves navigation performance by increasing network responsiveness, which is required to maintain a high degree of awareness in dynamic environments. The proposed strategies include a roadmap based navigation strategy coupled with two different query strategies called Roadmap Query (RQ) and Robust Roadmap Query (RRQ). The query strategies are optimized for the roadmap based navigation strategy, and are shown, through simulation under realistic fire scenarios, to outperform existing approaches in terms of both navigation performance and communication cost. We also present a mobile agent based implementation of RQ and provide empirical results of its performance on a Mica2 mote testbed.