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The Power of Abstraction
The Power of Abstraction Barbara Liskov March 2013 MIT CSAIL Software is Complex Systems are big and they do complicated things and they may be distributed and/or concurrent Addressing Complexity Algorithms, data structures, protocols Addressing Complexity Algorithms, data structures, protocols Programming methodology Programming languages This Talk Programming methodology as it developed Programming languages Programming languages today The Situation in 1970 The software crisis! Programming Methodology How should programs be designed? How should programs be structured? The Landscape E. W. Dijkstra. Go To Statement Considered Harmful. Cacm, Mar. 1968 The Landscape N. Wirth. Program Development by Stepwise Refinement. Cacm, April 1971 The Landscape D. L. Parnas. Information Distribution Aspects of Design Methodology. IFIP Congress, 1971 “The connections between modules are the assumptions which the modules make about each other.” Modularity A program is a collection of modules Modularity A program is a collection of modules Each module has an interface, described by a specification Modularity A program is a collection of modules Each has an interface, described by a specification A module’s implementation is correct if it meets the specification A using module depends only on the specification Modularity A program is a collection of modules Each has an interface, described by a specification A module’s implementation is correct if it meets the specification A using module depends only on the specification E.g. a sort routine sort(a) Benefits of Modularity Local reasoning Modifiability Independent development The Situation in 1970 Procedures were the only type of module Not powerful enough, e.g., a file system Not used very much Complicated connections Partitions B. -
QATAR ASW ONLINE SCRIPT V.8.0 Pages
“DEXIGN THE FUTURE: Innovation for Exponential Times” ARNOLD WASSERMAN COMMENCEMENT ADDRESS VIRGINIA COMMONWEALTH UNIVERSITY IN QATAR 2 MAY 2016 مساء الخير .Good afternoon It is an honor to be invited to address you on this important day. Today you artists and designers graduate into the future. Do you think about the future? Of course you do. But how do you think about the future? Is the future tangible - or is it intangible ? Is it a subject for rational deliberation? Or is it an imagined fantasy that forever recedes before us? Is the future simply whatever happens to us next? Or is it something we deliberately create? Can we Dexign the Future? What I would like us to think about for the next few moments is how creative professionals like yourselves might think about the future. What I have to say applies as much to art as it does to design. Both are technologies of creative innovation. I will take the liberty here of calling it all design. My speech is also available online. There you can follow a number of links to what I will talk about here. The future you are graduating into is an exponential future. What that means is that everything is happening faster and at an accelerating rate. For example, human knowledge is doubling every 12 months. And that curve is accelerating. An IBM researcher foresees that within a few years knowledge will be doubling every 12 hours as we build out the internet of things globally. This acceleration of human knowledge implies that the primary skill of a knowledge worker like yourself is research, analysis and synthesis of the not-yet-known. -
Computing Versus Human Thinking
By Peter Naur, recipient of ACM’s 2005 A.M. Turing Award Computing Versus Human Thinking n this presentation I shall give you an overview of efforts. Indeed, I have found that a large part of what Imy works from the past fifty years concerning the is currently said about human thinking and about sci- issue given in the title. Concerning this title I entific and scholarly activity is false and harmful to invite you to note particularly the middle word, ‘ver- our understanding. I realize that my presentation of sus’. This word points to the tendency of my efforts some of these issues may be offensive to you. This I around this theme, to wit, to clarify the contrast regret, but it cannot be avoided. between the two items, computing and human thinking. This tendency of my work has found its DESCRIPTION AS THE CORE ISSUE OF SCIENCE AND ultimate fulfilment in my latest result, which is a SCHOLARSHIP description of the nervous system showing that this The tone of critique and rejection of established system has no similarity whatever to a computer. ideas has its roots in my earliest activity, from its very It is ironic that my present award lecture is given beginning more than fifty years ago. Already in my under the title of Turing. As a matter of fact, one part work in astronomy, around 1955, a decisive item in of my work concerning computing and human think- my awareness came from Bertrand Russell’s explicit ing has been an explicit critique, or rejection, of the rejection of any notion of cause as a central issue of ideas of one prominent contribution from Alan Tur- scientific work. -
MIT Turing Laureates Propose Creation of School of Computing an Open Letter to President Rafael Reif
9/26/2017 The Tech OPINION LETTER TO THE EDITOR MIT Turing laureates propose creation of School of Computing An open letter to President Rafael Reif By MIT Turing Laureates | Sep. 20, 2017 Facebook Dear Rafael, Twitter There comes a time, in the course of scientic evolution, when a discipline is ready to emerge from the womb of its parent disciplines and take its own place in the world. For Reddit computer science, or more accurately, for the eld of computing, this moment is now. Print Born from a combination of mathematics and electrical engineering, with the original intent of speeding up calculations, computer science has grown to encompass all information processing and most communications and now to provide an alternative evolutionary path to intelligence. Computer science is rapidly becoming an essential part of most academic disciplines, and students are voting with their feet. One third of MIT undergraduates are majoring in computer science. This trend is unlikely to slow down anytime soon. We, the 7 active MIT Turing Award winners, therefore write this open letter to recommend that you consider the bold step of establishing a School of Computing at MIT. The new school, a brother to the Schools of Engineering and Science, will allow the eld of computing, with its many https://thetech.com/2017/09/20/turing-laureates-open-letter-to-reif 1/4 9/26/2017 The Tech facets and sub-elds, to grow and interact naturally with the Institute’s scientic and engineering environment. The Tech Submit Campus Life Stories Today the study of computation is housed primarily in the EECS department within the School of Engineering, but departments are limited in their ability to hire and grow. -
Object-Oriented Programming Basics with Java
Object-Oriented Programming Object-Oriented Programming Basics With Java In his keynote address to the 11th World Computer Congress in 1989, renowned computer scientist Donald Knuth said that one of the most important lessons he had learned from his years of experience is that software is hard to write! Computer scientists have struggled for decades to design new languages and techniques for writing software. Unfortunately, experience has shown that writing large systems is virtually impossible. Small programs seem to be no problem, but scaling to large systems with large programming teams can result in $100M projects that never work and are thrown out. The only solution seems to lie in writing small software units that communicate via well-defined interfaces and protocols like computer chips. The units must be small enough that one developer can understand them entirely and, perhaps most importantly, the units must be protected from interference by other units so that programmers can code the units in isolation. The object-oriented paradigm fits these guidelines as designers represent complete concepts or real world entities as objects with approved interfaces for use by other objects. Like the outer membrane of a biological cell, the interface hides the internal implementation of the object, thus, isolating the code from interference by other objects. For many tasks, object-oriented programming has proven to be a very successful paradigm. Interestingly, the first object-oriented language (called Simula, which had even more features than C++) was designed in the 1960's, but object-oriented programming has only come into fashion in the 1990's. -
An Early Program Proof by Alan Turing F
An Early Program Proof by Alan Turing F. L. MORRIS AND C. B. JONES The paper reproduces, with typographical corrections and comments, a 7 949 paper by Alan Turing that foreshadows much subsequent work in program proving. Categories and Subject Descriptors: 0.2.4 [Software Engineeringj- correctness proofs; F.3.1 [Logics and Meanings of Programs]-assertions; K.2 [History of Computing]-software General Terms: Verification Additional Key Words and Phrases: A. M. Turing Introduction The standard references for work on program proofs b) have been omitted in the commentary, and ten attribute the early statement of direction to John other identifiers are written incorrectly. It would ap- McCarthy (e.g., McCarthy 1963); the first workable pear to be worth correcting these errors and com- methods to Peter Naur (1966) and Robert Floyd menting on the proof from the viewpoint of subse- (1967); and the provision of more formal systems to quent work on program proofs. C. A. R. Hoare (1969) and Edsger Dijkstra (1976). The Turing delivered this paper in June 1949, at the early papers of some of the computing pioneers, how- inaugural conference of the EDSAC, the computer at ever, show an awareness of the need for proofs of Cambridge University built under the direction of program correctness and even present workable meth- Maurice V. Wilkes. Turing had been writing programs ods (e.g., Goldstine and von Neumann 1947; Turing for an electronic computer since the end of 1945-at 1949). first for the proposed ACE, the computer project at the The 1949 paper by Alan M. -
Simula Mother Tongue for a Generation of Nordic Programmers
Simula! Mother Tongue! for a Generation of! Nordic Programmers! Yngve Sundblad HCI, CSC, KTH! ! KTH - CSC (School of Computer Science and Communication) Yngve Sundblad – Simula OctoberYngve 2010Sundblad! Inspired by Ole-Johan Dahl, 1931-2002, and Kristen Nygaard, 1926-2002" “From the cold waters of Norway comes Object-Oriented Programming” " (first line in Bertrand Meyer#s widely used text book Object Oriented Software Construction) ! ! KTH - CSC (School of Computer Science and Communication) Yngve Sundblad – Simula OctoberYngve 2010Sundblad! Simula concepts 1967" •# Class of similar Objects (in Simula declaration of CLASS with data and actions)! •# Objects created as Instances of a Class (in Simula NEW object of class)! •# Data attributes of a class (in Simula type declared as parameters or internal)! •# Method attributes are patterns of action (PROCEDURE)! •# Message passing, calls of methods (in Simula dot-notation)! •# Subclasses that inherit from superclasses! •# Polymorphism with several subclasses to a superclass! •# Co-routines (in Simula Detach – Resume)! •# Encapsulation of data supporting abstractions! ! KTH - CSC (School of Computer Science and Communication) Yngve Sundblad – Simula OctoberYngve 2010Sundblad! Simula example BEGIN! REF(taxi) t;" CLASS taxi(n); INTEGER n;! BEGIN ! INTEGER pax;" PROCEDURE book;" IF pax<n THEN pax:=pax+1;! pax:=n;" END of taxi;! t:-NEW taxi(5);" t.book; t.book;" print(t.pax)" END! Output: 7 ! ! KTH - CSC (School of Computer Science and Communication) Yngve Sundblad – Simula OctoberYngve 2010Sundblad! -
Internet Engineering Jan Nikodem, Ph.D. Software Engineering
Internet Engineering Jan Nikodem, Ph.D. Software Engineering Theengineering paradigm Software Engineering Lecture 3 The term "software crisis" was coined at the first NATO Software Engineering Conference in 1968 by: Friedrich. L. Bauer Nationality;German, mathematician, theoretical physicist, Technical University of Munich Friedrich L. Bauer 1924 3/24 The term "software crisis" was coined at the first NATO Software Engineering Conference in 1968 by: Peter Naur Nationality;Dutch, astronomer, Regnecentralen, Niels Bohr Institute, Technical University of Denmark, University of Copenhagen. Peter Naur 1928 4/24 Whatshouldbe ourresponse to software crisis which provided with too little quality, too late deliver and over budget? Nationality;Dutch, astronomer, Regnecentralen, Niels Bohr Institute, Technical University of Denmark, University of Copenhagen. Peter Naur 1928 5/24 Software should following an engineering paradigm NATO conference in Garmisch-Partenkirchen, 1968 Peter Naur 1928 6/24 The hope is that the progress in hardware will cure all software ills. The Oberon System User Guide and Programmer's Manual. ACM Press Nationality;Swiss, electrical engineer, computer scientist ETH Zürich, IBM Zürich Research Laboratory, Institute for Media Communications Martin Reiser 7/24 However, a critical observer may notethat software manages to outgrow hardware in size and sluggishness. The Oberon System User Guide and Programmer's Manual. ACM Press Nationality;Swiss, electrical engineer, computer scientist ETH Zürich, IBM Zürich Research Laboratory, Institute for Media Communications Martin Reiser 8/24 Wirth's computing adage Software is getting slower more rapidly than hardware becomes faster. Nationality;Swiss, electronic engineer, computer scientist ETH Zürich, University of California, Berkeley, Stanford University University of Zurich. Xerox PARC. -
Arxiv:1909.05204V3 [Cs.DC] 6 Feb 2020
Cogsworth: Byzantine View Synchronization Oded Naor, Technion and Calibra Mathieu Baudet, Calibra Dahlia Malkhi, Calibra Alexander Spiegelman, VMware Research Most methods for Byzantine fault tolerance (BFT) in the partial synchrony setting divide the local state of the nodes into views, and the transition from one view to the next dictates a leader change. In order to provide liveness, all honest nodes need to stay in the same view for a sufficiently long time. This requires view synchronization, a requisite of BFT that we extract and formally define here. Existing approaches for Byzantine view synchronization incur quadratic communication (in n, the number of parties). A cascade of O(n) view changes may thus result in O(n3) communication complexity. This paper presents a new Byzantine view synchronization algorithm named Cogsworth, that has optimistically linear communication complexity and constant latency. Faced with benign failures, Cogsworth has expected linear communication and constant latency. The result here serves as an important step towards reaching solutions that have overall quadratic communication, the known lower bound on Byzantine fault tolerant consensus. Cogsworth is particularly useful for a family of BFT protocols that already exhibit linear communication under various circumstances, but suffer quadratic overhead due to view synchro- nization. 1. INTRODUCTION Logical synchronization is a requisite for progress to be made in asynchronous state machine repli- cation (SMR). Previous Byzantine fault tolerant (BFT) synchronization mechanisms incur quadratic message complexities, frequently dominating over the linear cost of the consensus cores of BFT so- lutions. In this work, we define the view synchronization problem and provide the first solution in the Byzantine setting, whose latency is bounded and communication cost is linear, under a broad set of scenarios. -
Design and Implementation of an Optionally-Typed Functional Programming Language
Design and Implementation of an Optionally-Typed Functional Programming Language Shaobai Li Electrical Engineering and Computer Sciences University of California at Berkeley Technical Report No. UCB/EECS-2017-215 http://www2.eecs.berkeley.edu/Pubs/TechRpts/2017/EECS-2017-215.html December 14, 2017 Copyright © 2017, by the author(s). All rights reserved. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. Design and Implementation of an Optionally-Typed Functional Programming Language by Patrick S. Li A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Engineering { Electrical Engineering and Computer Sciences in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Koushik Sen, Chair Adjunct Professor Jonathan Bachrach Professor George Necula Professor Sara McMains Fall 2017 Design and Implementation of an Optionally-Typed Functional Programming Language Copyright 2017 by Patrick S. Li 1 Abstract Design and Implementation of an Optionally-Typed Functional Programming Language by Patrick S. Li Doctor of Philosophy in Engineering { Electrical Engineering and Computer Sciences University of California, Berkeley Professor Koushik Sen, Chair This thesis describes the motivation, design, and implementation of L.B. Stanza, an optionally- typed functional programming language aimed at helping programmers tackle the complexity of architecting large programs and increasing their productivity across the entire software development life cycle. -
Structured Programming A.P.I.C
¢ . , v'~.1 c: STRUCTURED PROGRAMMING A.P.I.C. Studies in Data Processing General Editor: C. A. R. Hoare 1. Some Commercial Autocodes. A Comparative Study E. L. WiUey, A. d'Agapeyeff, Marion Tribe, B. J. Gibbens and Michelle Clarke. 2. A Primer of ALGOL 60 Programming E. W. Dijkstra 3. Input Language for Automatic Programming A. P. Yershov, G. I. Kozhukhin and U. Voloshin 4. Introduction to System Programming Edited by Peter Wegner 5. ALGOL 60 Implementation. The translation and use of Algol 60 Programs on a Computer B. RandeU and L. J. Russell 6. Dictionary for Computer Languages Hans Breuer 7. The Alpha Automatic Programming System Edited by A. P. Yershov 8. Structured Programming O.-J. Dahl, E. W. Dijkstra and C. A. R. Hoare In preparation Operating Systems Techniques Edited by C. A. R. Hoare and R. H. Perrott A.P.I.C. Studies in Data Processing No. 8 STRUCTURED PROGRAMMING O.-J. DAHL Universitet i Oslo, Matematisk Institut, Blindern, Oslo, Norway E. W. DIJKSTRA Department of Mathematics, Technological University, Eindhoven, The Netherlands C. A. R. HOARE Department of Computer Science, The Queen's University of Belfast, Belfast, Northern Ireland 1972 ACADEMIC PRESS LONDON AND NEW YORK ACADEMIC PRESS INC. (LONDON) LTD. 24]28 Oval Road, London NW1 United States Edition published by ACADEMIC PRESS INC. 111 Fifth Avenue New York, New York 10003 Copyright © 1972 by ACADEMIC PRESS INC. (LONDON) LTD. Second printing 1973 All Rights Reserved No part of this book may be reproduced in any form by photostat, microfilm, or any other means, without written permission from the publishers Library of Congress Catalog Card Number: 72-84452 ISBN: 0--12-200550-3 PRINTED IN GREAT BRITAIN BY WHITSTABLE LITHO~ STRAKER BROTHERS LTD. -
A Model of Inheritance for Declarative Visual Programming Languages
An Abstract Of The Dissertation Of Rebecca Djang for the degree of Doctor of Philosophy in Computer Science presented on December 17, 1998. Title: Similarity Inheritance: A Model of Inheritance for Declarative Visual Programming Languages. Abstract approved: Margaret M. Burnett Declarative visual programming languages (VPLs), including spreadsheets, make up a large portion of both research and commercial VPLs. Spreadsheets in particular enjoy a wide audience, including end users. Unfortunately, spreadsheets and most other declarative VPLs still suffer from some of the problems that have been solved in other languages, such as ad-hoc (cut-and-paste) reuse of code which has been remedied in object-oriented languages, for example, through the code-reuse mechanism of inheritance. We believe spreadsheets and other declarative VPLs can benefit from the addition of an inheritance-like mechanism for fine-grained code reuse. This dissertation first examines the opportunities for supporting reuse inherent in declarative VPLs, and then introduces similarity inheritance and describes a prototype of this model in the research spreadsheet language Forms/3. Similarity inheritance is very flexible, allowing multiple granularities of code sharing and even mutual inheritance; it includes explicit representations of inherited code and all sharing relationships, and it subsumes the current spreadsheet mechanisms for formula propagation, providing a gradual migration from simple formula reuse to more sophisticated uses of inheritance among objects. Since the inheritance model separates inheritance from types, we investigate what notion of types is appropriate to support reuse of functions on different types (operation polymorphism). Because it is important to us that immediate feedback, which is characteristic of many VPLs, be preserved, including feedback with respect to type errors, we introduce a model of types suitable for static type inference in the presence of operation polymorphism with similarity inheritance.