The essence of P2P: A reference architecture for overlay networks

The success of the P2P idea has created a huge diversity of approaches, among which overlay networks, for example, Gnutella, Kazaa, Chord, Pastry, Tapestry, P-Grid, or DKS, have received specific attention from both developers and researchers. A wide variety of algorithms, data structures, and architectures have been proposed. The terminologies and abstractions used, however, have become quite inconsistent since the P2P paradigm has attracted people from many different communities, e.g., networking, databases, distributed systems, graph theory, complexity theory, biology, etc. In this paper we propose a reference model for overlay networks which is capable of modeling different approaches in this domain in a generic manner. It is intended to allow researchers and users to assess the properties of concrete systems, to establish a common vocabulary for scientific discussion, to facilitate the qualitative comparison of the systems, and to serve as the basis for defining a standardized API to make overlay networks interoperable

Formal analysis techniques for gossiping protocols

We give a survey of formal verification techniques that can be used to corroborate existing experimental results for gossiping protocols in a rigorous manner. We present properties of interest for gossiping protocols and discuss how various formal evaluation techniques can be employed to predict them

A Survey of User Interfaces for Computer Algebra Systems

AbstractThis paper surveys work within the Computer Algebra community (and elsewhere) directed towards improving user interfaces for scientific computation during the period 1963–1994. It is intended to be useful to two groups of people: those who wish to know what work has been done and those who would like to do work in the field. It contains an extensive bibliography to assist readers in exploring the field in more depth. Work related to improving human interaction with computer algebra systems is the main focus of the paper. However, the paper includes additional materials on some closely related issues such as structured document editing, graphics, and communication protocols

Efficient geographic information systems: Data structures, Boolean operations and concurrency control

Geographic Information Systems (GIS) are crucial to the ability of govern mental agencies and business to record, manage and analyze geographic data efficiently. They provide methods of analysis and simulation on geographic data that were previously infeasible using traditional hardcopy maps. Creation of realistic 3-D sceneries by overlaying satellite imagery over digital elevation models (DEM) was not possible using paper maps. Determination of suitable areas for construction that would have the fewest environmental impacts once required manual tracing of different map sets on mylar sheets; now it can be done in real time by GIS. Geographic information processing has significant space and time require ments. This thesis concentrates on techniques which can make existing GIS more efficient by considering these issues: Data Structure, Boolean Operations on Geographic Data, Concurrency Control. Geographic data span multiple dimensions and consist of geometric shapes such as points, lines, and areas, which cannot be efficiently handled using a traditional one-dimensional data structure. We therefore first survey spatial data structures for geographic data and then show how a spatial data structure called an R-tree can be used to augment the performance of many existing GIS. Boolean operations on geographic data are fundamental to the spatial anal ysis common in geographic data processing. They allow the user to analyze geographic data by using operators such as AND, OR, NOT on geographic ob jects. An example of a boolean operation query would be, Find all regions that have low elevation AND soil type clay. Boolean operations require signif icant time to process. We present a generalized solution that could significantly improve the time performance of evaluating complex boolean operation queries. Concurrency control on spatial data structures for geographic data processing is becoming more critical as the size and resolution of geographic databases increase. We present algorithms to enable concurrent access to R-tree spatial data structures so that efficient sharing of geographic data can occur in a multi user GIS environment

End-to-End Error-Correcting Codes on Networks with Worst-Case Symbol Errors

The problem of coding for networks experiencing worst-case symbol errors is considered. We argue that this is a reasonable model for highly dynamic wireless network transmissions. We demonstrate that in this setup prior network error-correcting schemes can be arbitrarily far from achieving the optimal network throughput. A new transform metric for errors under the considered model is proposed. Using this metric, we replicate many of the classical results from coding theory. Specifically, we prove new Hamming-type, Plotkin-type, and Elias-Bassalygo-type upper bounds on the network capacity. A commensurate lower bound is shown based on Gilbert-Varshamov-type codes for error-correction. The GV codes used to attain the lower bound can be non-coherent, that is, they do not require prior knowledge of the network topology. We also propose a computationally-efficient concatenation scheme. The rate achieved by our concatenated codes is characterized by a Zyablov-type lower bound. We provide a generalized minimum-distance decoding algorithm which decodes up to half the minimum distance of the concatenated codes. The end-to-end nature of our design enables our codes to be overlaid on the classical distributed random linear network codes [1]. Furthermore, the potentially intensive computation at internal nodes for the link-by-link error-correction is un-necessary based on our design.Comment: Submitted for publication. arXiv admin note: substantial text overlap with arXiv:1108.239

Het stapelen van ruimtelijke informatie: Enkele gedachten over het structureren in lagen en de oorsprong ervan

Understood as a conceptual tool for the manage­ment of information, layers are ubiquitous in our days. In computer graphics, they are a standard, basic feature: image editors for still or motion pic­tures, computer­assisted drawing (CAD) pro­grams, and of course geospatial information sys­tems (GIS) – as well as most of their user­oriented applications –, all of them use layers in one way or another, often in so essential a manner that they constitute their very raison d’être. As a conse­quence, the catchy word layering that so much pervades current architectural practice seems to designate something that everyone knows, a procedure that is practically taken for granted and yet has given rise to comparatively little research. In relation to architectural design, this may be par­ticularly baffling, considering that layering has provided the backbone for singular projects that have become a methodological breakthrough and an inexhaustible source of inspiration for subse­quent practice – one needs only to think of Kool­haas’ influential proposal for Parc de la Villette, Eisenman’s recurrent lucubrations, or the recent Serpentine pavilion by Herzog de Meuron and Ai Weiwei.Layers of ‘lagen’, opgevat als een begripsinstru­ment voor het beheer van informatie, zijn in onze tijd alomtegenwoordig. Ze zijn een primair en vast kenmerk van computergraphics: beeldbewerkings­programma’s voor stilstaande of bewegende beel­den, digitale tekenprogramma’s (CAD) en natuur­lijk geografische informatiesystemen (GIS) en de meeste van hun gebruiksgerichte applicaties, ze maken allemaal op de een of andere manier gebruik van gelaagde informatie, en vaak zijn die lagen er zo’n wezenlijk bestanddeel van dat ze hun raison d’être zelf vormen. De kreet layering, die in de huidige architectuurpraktijk zo wijdverbreid is, lijkt als gevolg daarvan te slaan op iets wat ieder­een kent, een procedé dat nagenoeg als vanzelf­sprekend wordt aangenomen en toch maar relatief weinig is onderzocht. Dat laatste is bij uitstek ver­bazingwekkend in de context van het architec­tuurontwerp, als we bedenken dat het structure­ren in lagen heeft gefungeerd als de ruggengraat van uitzonderlijke ontwerpen die gelden als een methodologische doorbraak en onuitputtelijke bron van inspiratie voor volgende generaties: denk alleen maar aan het invloedrijke voorstel van Rem Koolhaas voor Parc de la Villette, Eisenmans tech­nische hoogstandjes of het recente Serpentine Gallery Pavilion van Herzog & de Meuron en Ai Weiwei