The Social Psychology of Organizations.

J+=j

Apercu sur les quadarbres et les structures de donnees hierarchiques. Elles sont basees sur le principe de decomposition recursive. L'accentuation est mise sur la representation de donnees dans les applications de traitement d'images, d'infographie, les systemes d'informations geographiques et la robotique. On examine en detail un certain nombre d'operations dans lesquelles de telles structures de donnees trouvent leur utilisation

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The Quadtree and Related Hierarchical Data Structures

While the course of technological change is widely accepted to be highly uncertain and unpredictable, little work has identified or studied the ultimate sources and causes of that uncertainty. This paper proposes that purely technological uncertainty derives from inventors' search processes with unfamiliar components and component combinations. Experimentation with new components and new combinations leads to less useful inventions on average, but it also implies an increase in the variability that can result in both failure and breakthrough. Negative binomial count and dispersion models with patent citation data demonstrate that new combinations are indeed more variable. In contrast to predictions, however, the reuse of components has a nonmonotonic and eventually positive effect on variability.

/pdf/recombinant-uncertainty-in-technological-search-4rm3o5a2zv.pdf

Recombinant Uncertainty in Technological Search

Motivated by the properties of spreading activation and conceptual distance, the authors propose a metric, called distance, on the power set of nodes in a semantic net. Distance is the average minimum path length over all pairwise combinations of nodes between two subsets of nodes. Distance can be successfully used to assess the conceptual distance between sets of concepts when used on a semantic net of hierarchical relations. When other kinds of relationships, like 'cause', are used, distance must be amended but then can again be effective. The judgements of distance significantly correlate with the distance judgements that people make and help to determine whether one semantic net is better or worse than another. The authors focus on the mathematical characteristics of distance that presents novel cases and interpretations. Experiments in which distance is applied to pairs of concepts and to sets of concepts in a hierarchical knowledge base show the power of hierarchical relations in representing information about the conceptual distance between concepts. >

Development and application of a metric on semantic nets

A systematic procedure is presented for writing a Boolean function as a minimum sum of products This procedure is a simplification and extension of the method presented by W V Quine Specific attention is given to terms which can be included in the function solely for the designer's convenience

Minimization of Boolean functions

Concurrent system-level error detection techniques using a watchdog processor are surveyed. A watchdog processor is a small and simple coprocessor that detects errors by monitoring the behavior of a system. Like replication, it does not depend on any fault model for error detection. However, it requires less hardware than replication. It is shown that a large number of errors can be detected by monitoring the control flow and memory-access behavior. Two techniques for control-flow checking are discussed and compared with current error-detection techniques. A scheme for memory-access checking based on capability-based addressing is described. The design of a watchdog for performing reasonable checks on the output of a main processor by executing assertions is discussed. >

/pdf/concurrent-error-detection-using-watchdog-processors-a-2tshpt2hpe.pdf

Concurrent error detection using watchdog processors-a survey

This paper presents a new signature monitoring technique, CFCSS (control flow checking by software signatures); CFCSS is a pure software method that checks the control flow of a program using assigned signatures. An algorithm assigns a unique signature to each node in the program graph and adds instructions for error detection. Signatures are embedded in the program during compilation time using the constant field of the instructions and compared with run-time signatures when the program is executed. Another algorithm reduces the code size and execution time overhead caused by checking instructions in CFCSS. A "branching fault injection experiment" was performed with benchmark programs. Without CFCSS, an average of 33.7 % of the injected branching faults produced undetected incorrect outputs; however, with CFCSS, only 3.1 % of branching faults produced undetected incorrect outputs. Thus it is possible to increase error detection coverage for control flow errors by an order of magnitude using CFCSS. The distinctive advantage of CFCSS over previous signature monitoring techniques is that CFCSS is a pure software method, i.e., it needs no dedicated hardware such as a watchdog processor for control flow checking. A watchdog task in multitasking environment also needs no extra hardware, but the advantage of CFCSS over a watchdog task is that CFCSS can be used even when the operating system does not support multitasking.

Control-flow checking by software signatures

This paper proposes a pure software technique "error detection by duplicated instructions" (EDDI), for detecting errors during usual system operation. Compared to other error-detection techniques that use hardware redundancy, EDDI does not require any hardware modifications to add error detection capability to the original system. EDDI duplicates instructions during compilation and uses different registers and variables for the new instructions. Especially for the fault in the code segment of memory, formulas are derived to estimate the error-detection coverage of EDDI using probabilistic methods. These formulas use statistics of the program, which are collected during compilation. EDDI was applied to eight benchmark programs and the error-detection coverage was estimated. Then, the estimates were verified by simulation, in which a fault injector forced a bit-flip in the code segment of executable machine codes. The simulation results validated the estimated fault coverage and show that approximately 1.5% of injected faults produced incorrect results in eight benchmark programs with EDDI, while on average, 20% of injected faults produced undetected incorrect results in the programs without EDDI. Based on the theoretical estimates and actual fault-injection experiments, EDDI can provide over 98% fault-coverage without any extra hardware for error detection. This pure software technique is especially useful when designers cannot change the hardware, but they need dependability in the computer system. To reduce the performance overhead, EDDI schedules the instructions that are added for detecting errors such that "instruction-level parallelism" (ILP) is maximized. Performance overhead can be reduced by increasing ILP within a single super-scalar processor. The execution time overhead in a 4-way super-scalar processor is less than the execution time overhead in the processors that can issue two instructions in one cycle.

Error detection by duplicated instructions in super-scalar processors

In this correspondence two methods are given for calculating the probability that the output of a general combinational network is 1 given the probabilities for each input being 1. We define the notions of the probability of a signal and signal independence. Then several proofs are given to show the relationship between Boolean operations and algebraic operations upon probabilities. As a result of these, two simple algorithms are presented for calculating output probabilities. An example of the usefulness of these results is given with respect to the generation of tests for the purpose of fault detection.

Edward J. McCluskey

Papers

Minimization of Boolean functions

Concurrent error detection using watchdog processors-a survey

Control-flow checking by software signatures

Error detection by duplicated instructions in super-scalar processors

Probabilistic Treatment of General Combinational Networks